PCC September October 2021 e

September / October 2021 

Don’t Let Phosphorus Erode Away 

VINEYARD REVIEW 

Activator Spray Adjuvant Selection in 

Trees and Vines 

LODI RULES for Sustainable Winegrowing: 

A Quality Winegrape Program 

Nitrogen Fertilization Alters Phosphorus 

Status of Grapevines 

September 16-17, 2021 - Visalia, California 

Register at progressivecrop.com/conference 

SEE PAGE 38-39 FOR MORE INFORMATION 

Volume 6: Issue 5

4 

IN THIS ISSUE 

Nitrogen Regulations 

in California and the 

Certified Crop Adviser’s 

Role 

PUBLISHER: Jason Scott 

Email: jason@jcsmarketinginc.com 

EDITOR: Marni Katz 

ASSOCIATE EDITOR: Cecilia Parsons 

Email: article@jcsmarketinginc.com 

PRODUCTION: design@jcsmarketinginc.com 

Phone: 559.352.4456 

Fax: 559.472.3113 

Web: www.progressivecrop.com 

CONTRIBUTING WRITERS & INDUSTRY SUPPORT 

8 

14 

18 

New Knowledge-Based 

Information Developed 

to Enhance Water and 

Nitrogen Use Efficiency 

in Desert Fresh Market 

Carrots 

Don’t Let Phosphorus 

Erode Away 

Ongoing University 

of California Hemp 

Research to Address 

Water, N issues 

4 

Mark Cady 

Senior Environmental 

Scientist, California 

Department of Food and 

Agriculture, Fertilizer 

Research and Education 

Program 

Michael Cahn 

UCCE Irrigation and Water 

Resources Advisor, Monterey 

County 

Daniel Geisseler 

Nutrient Management 

Specialist, UC Davis 

Ali Montazar 

UCCE Irrigation and Water 

Management Advisor, 

Imperial County 

Franz Niederholzer 

UCCE Farm Advisor, Colusa 

and Sutter/Yuba Counties 

Clifford P. Ohmart, Ph.D. 

Ohmart Consulting Services 

Jerome Pier 

Chair, Western Region 

Certified Crop Advisers 

Association 

Rhonda Smith 

UCCE Farm Advisor, Sonoma 

County 

Tian Tian 

UCCE Area Viticulture Farm 

Advisor, Kern County 

Jeannette E. Warnert 

Communications Specialist, 

UC ANR 

Eryn Wingate 

Agronomist, Tri-Tech Ag 

Products, Inc. 


22 

26 

32 

Activator Spray Adjuvant 

Selection in Trees and 

Vines 

LODI RULES 

for Sustainable 

Winegrowing: A Quality 

Winegrape Program 

Nitrogen Fertilization 

Alters Phosphorus Status 

of Grapevines and 

Their Association with 

Arbuscular Mycorrhizal 

Fungi 

22 

32 

UC COOPERATIVE EXTENSION 

ADVISORY BOARD 

Surendra Dara 

UCCE Entomology and 

Biologicals Advisor, San Luis 

Obispo and Santa Barbara 

Counties 

Kevin Day 

UCCE Pomology Farm Advisor, 

Tulare and Kings Counties 

Elizabeth Fichtner 

UCCE Farm Advisor, 

Kings and Tulare Counties 

Katherine Jarvis-Shean 

UCCE Orchard Systems 

Advisor, Sacramento, Solano 

and Yolo Counties 

Steven Koike 

Tri-Cal Diagnostics 

Jhalendra Rijal 

UCCE Integrated Pest 

Management Advisor, 

Stanislaus County 

Kris Tollerup 

UCCE Integrated Pest Management 

Advisor, Fresno, CA 

Mohammad Yaghmour 

UCCE Area Orchard Systems 

Advisor, Kern County 

The articles, research, industry updates, company profiles, and advertisements 

in this publication are the professional opinions of writers 

and advertisers. Progressive Crop Consultant does not assume any 

responsibility for the opinions given in the publication. 

September / October 2021 www.progressivecrop.com 3

Nitrogen Regulations in 

California and the Certified 

Crop Adviser’s Role 

By MARK CADY | Senior Environmental Scientist, California Department of Food and Agriculture, 

Fertilizer Research and Education Program 

and JEROME PIER | Chair, Western Region Certified Crop Advisers Association 

California Certified Crop Advisers (CCAs) are an integral part of the nitrogen management compliance picture (all photos by Vicky Boyd.) 

In the last 10 or more years, water 

quality regulations that address nitrate 

in groundwater have expanded 

dramatically. Starting in 2012, the regulatory 

agencies charged with protecting 

California’s water quality have increased 

their scrutiny of and demands on 

agriculture. So, it is essential for crop 

consultants to understand the regulations 

and how regulations affect their 

customers. 

Regulatory History 

The challenges associated with nitrate 

in groundwater and its sources have 

been recognized for at least a generation. 

In 1987, the California State 

Legislature directed the State Water 

Resources Control Board to prepare 

a report on nitrate contamination in 

drinking water. The convened expert 

panel reported that agriculture was 

likely an important contributor to 

nitrate in groundwater. 

In 2012, however, the regulatory 

landscape changed dramatically. First, 

a major study of nitrate in California 

drinking water was published by UC 

Davis. This sprawling effort, titled 

Addressing Nitrate in California’s 

Drinking Water, focused on the Tulare 

Lake Basin and the Salinas Valley. The 

multi-volume report was produced by 

the UC Davis Center for Watershed 

Sciences. It showed that nitrate problems 

would likely worsen for the next 

several decades and that most nitrate 

currently in drinking water wells was 

applied to the surface decades earlier. 

An important conclusion of the report 

was that agricultural fertilizers and 

animal wastes applied to cropland are 

by far the largest regional sources of 

nitrate in groundwater. Thus, in the last 

decade, the State and Regional Water 

Boards have been more assertive in 

regulating agricultural contributions to 

groundwater nitrate. 

The Central Valley Irrigated Lands Regulatory 

Program (ILRP) started in the 

first part of this century with a focus on 

pesticides in surface water. That focus 

expanded in 2012 when the ‘Waste 

Discharge Requirements for the Eastern 

San Joaquin River Watershed (ESJ) 

General Order’ was first adopted by the 

Central Valley Regional Water Quality 

Control Board (CVRWQCB). This order 

required grower reporting of nitrogen 

fertilizer applied to cropland and 

estimates of the nitrogen removed with 

harvested crops, so the efficiency of 

nitrogen fertilizer use could be calculated. 

Growers record this information 

in their Nitrogen Management Plans 

(NMPs) as specified by the CVRWQCB. 

The reporting of NMP data was carried 

out through the ESJ Water Quality 

Coalition, a grower-led intermediary 

that anonymized the data and provided 

statistical analysis on a township basis. 

A component of the statistical analysis 

is identification of outlier values (i.e., 

parcels where the nitrogen efficiency 

Continued on Page 6 

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Continued from Page 4 

is low relative to others in township.) 

These outlier growers are then targeted 

for outreach and increasing reporting 

requirements. Growers in all regions of 

the Central Valley are represented by 

coalitions. Nitrogen reporting requirements 

are now in place for all Central 

Valley regions and crops with the 

exception of rice. 

In 2018, the State Water Board stepped 

into the picture and revised the ESJ 

Order to include new provisions to be 

precedential to all regional boards. The 

precedents adopted include reporting 

of nitrogen application (A) to and removal 

(R) from cropland, reporting of 

irrigation water used, testing on-farm 

domestic wells for nitrate and reporting 

nitrate exceedances to the well 

users. With these new requirements, 

the NMPs became the Irrigation and 

Nitrogen Management Plans (INMPs). 

The regional boards were directed to 

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available Phosphorus. 

Earthworms are able to do their best work in soil 

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use both A/R and A-R (the nitrogen 

efficiency ratio and the total excess 

nitrogen, respectively) to evaluate 

compliance. All regional boards are 

required to adopt these precedents into 

orders by February 2023. The CVR- 

WQCB updated its ILRP orders in 2019. 

Another major nitrate-related regulatory 

effort in the Central Valley is the 

Central Valley Salinity Alternatives for 

Long-Term Sustainability (CV-SALTS). 

This is a multi-stakeholder effort that 

seeks to manage the long-term loading 

of salts in the Central Valley. Of 

interest here is the focus on nitrate. The 

CVRWQCB adopted the regulations 

proposed by the CV-SALTS stakeholders 

in 2018. The goals of CV-SALTS 

regulations are “1) to ensure a safe 

drinking water supply; 2) to achieve 

balanced salt and nitrate loadings; 

and 3) to implement long-term and 

managed aquifer restoration programs 

where reasonable, feasible and practicable.” 

While the CV- 

SALTS process 

affects all discharges 

in the Central 

Valley, each of the 

above goals represent 

challenges to 

growers in terms of 

costs of compliance 

and improving 

nitrogen fertilizer 

management. Fortunately 

for growers, 

the administration 

of regulatory 

requirements is 

handled by the 

coalitions that were 

established for the 

ILRP. 

Looking again at 

2012, the Central 

Coast Regional Water 

Quality Control 

Board (CCRWQCB) 

adopted its first 

order to require reporting 

of nitrogen 

applications. This 

information was 

reported directly to the Regional Water 

Board. Just this year, the CCRWQCB 

adopted the updated “Ag Order 4.0,” 

incorporating the ESJ precedents and 

setting long-term limits on excess 

nitrogen applied to crops. Farming operations 

must now submit information 

on nitrogen applied to and removed 

from cropland. The order includes a 

schedule of targets for excess nitrogen 

fertilizer roughly defined as A-R. After 

2026, specific excess nitrogen targets 

are in place for all crops. Those targets 

rachet down from 300 lbs/ac in 2026 to 

just 50 lbs/ac in 2050. For reference, the 

CCRWQCB estimates that currently 

only approximately 6% of the acres of 

high-value crops meet the 2050 benchmark. 

The situation in the Central Valley is 

different than in the Central Coast. The 

Central Valley coalitions have developed 

a methodology to determine what 

those targets should be on a township 

basis. The methodology, a sophisticated 

modelling effort for the entire 

Central Valley, has been approved by 

the CVRWQCB Executive Officer and 

is scheduled to produce target excess 

nitrogen values in 2023. 

The Crop Adviser’s Role 

California Certified Crop Advisers 

(CCAs) are an integral part of the 

nitrogen management compliance picture. 

The CVRWQCB determined that 

CCAs who received special training 

in nitrogen management are qualified 

to certify growers’ INMPs. There are 

now nearly 900 CCAs eligible to certify 

INMPs. 

For several years, CCAs became eligible 

to certify Central Valley growers’ 

NMPs through training received via a 

day-and-a-half in-person conference 

given once a year and presented by UC 

faculty. Funded by the CDFA Fertilizer 

Research and Education Program 

(FREP), this successfully certified nearly 

1,000 CCAs. On October 1, 2020, the 

certification program changed to a Nitrogen 

Management Specialty category 

managed by the International Certified 

Crop Adviser organization. All CCAs 

who had the nitrogen management certification 

were “grandfathered” into the 


new Nitrogen Management Specialty 

category. CCAs who had not yet been 

certified now must take the Nitrogen 

Specialty category exam to be qualified 

to sign INMPs. UC staff developed online 

training modules to assist CCAs 

in passing the specialty exam. The 

training is available to any CCA and 

provides 16 continuing education units 

(CEUs) for a cost of $120. More information 

regarding the online training 

and the specialty exam can be found 

at certifiedcropadvisor.org/ca-nsp/. 

CCAs who have the California Nitrogen 

Management Specialty (CA-NSP) 

category must obtain eight CEUs in 

nutrient management and seven CEUs 

in soil and water management over 

two years but are still only required to 

obtain 40 total CEUs to maintain their 

certification. There is an additional fee 

required to maintain the CA-NSP. 

CCAs may find that certifying INMPs, 

especially the irrigation portions of the 

forms, moves them out of the nutrient 

management comfort zones. Because 

we all recognize the importance of 

irrigation management in nitrogen 

management, we can also realize that 

it’s a crucial area for CCAs to step into. 

Information regarding anticipated 

crop evapotranspiration (ETc) and irrigation 

water to be applied is required 

in the INMPs. Instructions provided 

with the plans suggest that the UC or 

coalition may provide the information 

to complete the ETc question, but 

the data are not readily available. To 

resolve the conflicts involving ETc 

determination, a statewide project was 

funded to create an accepted clearinghouse 

of coefficient values for the 

major crops in California. The project 

is nearing completion and should go 

a long way to helping CCAs provide 

accurate answers for the ETc questions 

in the INMP. Alternatively, this 

year, a project involving the National 

Aeronautics and Space Administration 

(NASA), the Environmental Defense 

Fund and a host of other partners will 

make ETc data available through interactive 

maps on the web. The project is 

called OpenET and is set to be released 

by the end of the year. 

FREP is holding its annual conference 

this year in San Luis Obispo from October 

26-28. There will be sessions on 

OpenET, ILRP water quality coalitions 

and other nutrient and irrigation management 

topics. For more information, 

see cdfa.ca.gov/is/ffldrs/frep/FREP- 

Conference.html. 

Mark Cady is currently supervisor of 

the CDFA FREP. His understanding of 

water quality regulation comes from 

four years as an environmental scientist 

with the CVRWQCB. FREP’s role is to 

fund and facilitate research and education 

to advance the environmentally 

safe and agronomically sound use and 

handling of fertilizing materials. Please 

visit cdfa.ca.gov/is/ffldrs/frep for more 

information. 

Comments about this article? We want 

to hear from you. Feel free to email us 

at article@jcsmarketinginc.com 

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New Knowledge-Based Information 

Developed to Enhance Water and 

Nitrogen Use Efficiency in Desert 

Fresh Market Carrots 

By ALI MONTAZAR | UCCE Irrigation and Water Management Advisor, Imperial County 

DANIEL GEISSELER | Nutrient Management Specialist, UC Davis 

and MICHAEL CAHN | UCCE Irrigation and Water Resources Advisor, Monterey County 

Carrot field under furrow irrigation system in the Imperial Valley (all photos by A. Montazar.) 

Carrots are one of the 10 major 

commodities in Imperial County, 

with an average acreage of nearly 

16,000 over the past decade. The farm 

gate value of fresh market and processing 

carrots was about $66 million 

in 2019. In the low desert region, fresh 

market and processing carrots are planted 

from September to December for 

harvest from January to May. Most carrots 

are typically sprinkler irrigated for 

stand establishment and subsequently 

furrow irrigated for the remainder of 

the growing season. However, there 

are fields that are irrigated by solid set 

sprinkler systems the entire crop season. 

Carrot is a cool-season crop that demands 

specific growing conditions and 

effective use of nitrogen (N) and water 

applications for successful commercial 

production. N and water management 

in carrot is crucial for increasing crop 

productivity and decreasing costs and 

nitrate leaching losses. The N needs of 

carrots for optimum storage root yield 

depends on the climate, soil texture 

and conditions, residual soil N from 

the previous season and irrigation 

management. There is not enough 

research on N management to free 

local growers of the worry associated 

with being short on the amounts 

applied, which may cause a loss in 

yield and profitability. The industry 

needs reliable information on N and 

consumptive water use of carrots to 

optimize irrigation and N management, 

enhance water and nitrogen use efficiency 

and achieve full economic gains 

in a sustainable soil and water quality 

approach. 

This study aimed to quantify optimal 

N and water applications under current 

management practices and to fill 

knowledge gaps for N and water management 

in carrots through conducting 

experimental trials in the low desert of 

California. This article presents some 

of the information developed for desert 

fresh market carrots. 

Field Trials and Measurements 

Field trials were conducted on fresh 

market carrot cultivars at the UC 

Desert Research and Extension Center 

(DREC) and four commercial fields in 

the low desert region during the 2019- 

20 and 2020-21 seasons (Table 1, see 

page 10). The sites represent various 

aspects of nitrogen applied (N applications 

ranged between 176 and 272 lbs 

ac -1 ), irrigation water applied (varied 

from 1.6 to 2.9 ac-feet/ac), irrigation 

systems (three fields under sprinkler 

irrigation and two fields under furrow 

irrigation) and soil types (sandy loam 

to silty clay loam). 

The DREC trials consisted of two 

irrigation regimes and three nitrogen 

scenarios (Fig. 2, see page 10). At the 

commercial sites, due to logistical 

limitations, the measurements were 

carried out from five sub-areas selected 

(50 feet x 50 feet) in an experimental 

assigned plot (400 feet x 400 feet) with 

a homogeneous soil type, which was 

the dominant soil at the site. These 

areas represented common irrigation 

and N fertilizer management practices 

followed by growers. 

The actual consumptive water use 

(actual crop evapotranspiration (ET)) 

was measured using the residual of the 

energy balance method with a combination 

of surface renewal and eddy 

covariance equipment (fully automated 

ET tower, Fig. 3, see page 10). As an 

affordable tool to estimate actual crop 

ET, Tule Technology sensors were also 

set up at all experimental sites. The 

Tule ET data were verified using the 

ET estimates from the fully automated 

ET tower. Canopy images were taken 

on weekly to a 15-day basis utilizing an 

infrared camera (NDVI digital camera) 

to quantify crop canopy coverage over 

the crop season. Actual soil nitrate content 

(NO 3 

-N) at the crop root zone (one 

to five feet) and the total N percentage 

in tops and roots were determined 

pre-seeding, post-harvest and monthly 

over the season. Plant measurements 

were carried out on 40-plant samples 

collected randomly per replication of 

each treatment/sub-area, and deter- 



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Experimental Site Seeding (first irrigation) Date Harvest Date Irrigation Practices 

DREC-1 

Oct 11, 2019 

Mar 18, 2020 

Sprinker 

DREC-2 

Oct 14, 2020 

Mar 21, 2021 

Sprinker 

C1 

Oct 24, 2019 

Mar 30, 2020 

Sprinker 

C2 

Oct 2, 2019 

Mar 19, 2020 

Furrow 

C3 

Oct 4, 2019 

Mar 17, 2020 

Furrow 

C4 

Oct 2, 2020 

Apr 12, 2021 

Sprinker 

Table 1: General information for the experimental sites. Plants were established using sprinkler irrigation at all sites. 


minations were made on marketable 

yield and biomass accumulation. Fresh 

weight and dry weight of roots and foliage 

were measured on a regular basis. 

Findings and Recommendations 

Irrigation Management 

The common irrigation practice in 

carrot stand establishment in the low 

desert is to irrigate the field every other 

day using sprinkler systems during the 

first two weeks after seeding. Carrots 

germinate slowly, and hence, the beds 

need to be kept moist to prevent crusting. 

A comparison between the averages 

of applied water and actual consumptive 

water use for a 30-day period 

after seeding suggested that carrots are 

typically over-irrigated during plant 

establishment. An average of 3.8 inches 

was measured as actual consumptive 

water use for this period across the 

experimental sites (Fig. 4, see page 12), 

while the applied water varied from 

two to three times of this amount. 

The results clearly demonstrated that 

the carrot sites had variable actual consumptive 

water uses depending upon 

early/late planting, irrigation practice, 

length of crop season, soil type and 

weather conditions. For instance, site 

C-4 was a sprinkler irrigated field with 

a dominant soil texture of sandy clay 

loam where the carrots were harvested 

very late 193 days after seeding (DAS). 

The seasonal consumptive water use 

was 19.2 inches at this site (Fig. 4, see 

page 12). Our results show that the 

seasonal crop water use of fresh market 

carrots is nearly 16.0 inches for a typical 

crop season of 160 days with planting 

in October. Approximately 50% of 

crop water needs occurred during the 

first 100 days after seeding and the other 

50% during the last 60 days before 

harvest. Crop canopy model developed 

in this study demonstrated that fresh 

market carrots reach 85% canopy coverage 

by 100 days after seeding. 

The amount of water that needs to be 

applied in an individual field depends 

on crop water requirements and the 

efficiency of the irrigation system. 

Assuming an average irrigation efficiency 

of 70%, the approximate gross 

irrigation water needs of carrot fields 

in the low desert would be 2.0 ac-feet/ 

ac (pre-irrigation is not included) for 

a 160-day crop season. Pre-irrigation 

along with proper irrigation scheduling 

over the season may effectively maintain 

crop water needs and salinity in 

carrots. 

Water stress should be avoided 

throughout the carrot growing cycle. 

The critical period for irrigation is 

between fruit set and harvest. Sprinkler 

irrigation may be considered as a more 

effective irrigation tool when compared 

with furrow irrigation. More frequent 

and light irrigation events are possible 

by sprinkler irrigation. Over-irrigation 

of carrot fields increases the incidence 

of hairy roots, and severe drying and 

wetting cycles result in significant 

splitting of roots. Sprinklers also reduce 

salinity issues which is important 

since carrots are very sensitive to salt 

accumulation. 


Figure 2: The DREC trials consisted of two irrigation regimes and 

three nitrogen scenarios. 

Figure 3: Monitoring stations in one of the commercial experimental 

sites. 


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Figure 5: Canopy development curve for the low desert fresh market carrots over the 

growing season. 

Figure 4: Cumulative actual crop water consumption 

(actual ET) at each of the experimental sites. Surface 

renewal actual daily ET is reported here. 

Nitrogen Management 

The results demonstrated that a wide 

range of N accumulated both in roots 

and tops at harvest (Fig. 6). For instance, 

a total N content of 312.9 lbs 

ac -1 was observed in a fresh market 

carrot field with a long growing season 

of 193 days, including 202.9 and 

110.0 lbs N ac -1 in roots and tops, 

respectively. The total N accumulated 

in plants (roots + tops) was 

less than 265 lbs ac -1 in the other 

sites. 

A linear regression model was 

found for the total N uptake in 

roots after 60 to 73 DAS without 

declining near harvest (Fig. 6). 

Small, gradual increases in N 

contents of roots were observed 

until about 65 DAS. This suggested 

that N begins to accumulate 

at a rapid rate between 65 and 

80 DAS; however, the period 

of rapid increase could vary 

depending on early (September) 

or late (November) plantings. 

N uptake in tops increased 

gradually following a quadratic 

regression, and in most sites 

levelled off or declined slightly 

late in the season. Although the 

N accumulated in tops appeared 

Figure 6: N accumulation trends in storage roots, 

to drop down or level off in most 

tops and total (plants) over the growing season at the 

sites beyond 120 to 145 DAS, the 

experimental sites. 

N content decline occurred after 

DAS 155 at site C-4 with a longer 

growing season. 


These findings suggest that a total N 

accumulation of 260 lbs ac -1 occurred 

by 160 DAS, with 145 lbs ac -1 in roots 

and 115 lbs ac -1 in tops. Across all sites, 

nearly 28% of seasonal N accumulation 

occurred by 80 DAS (Fig. 6) when 

the canopy cover reached an average 

of 67% (Fig. 5). The large proportion 

of this N content was taken up during 

a 30-day period (50 to 80 DAS). The 

results also suggest that nearly 50% of 

the total N was taken up during a 50- 

day period (80 to 130 DAS). This 50-day 

period appears to be the most critical 

period for N uptake, particularly in the 

storage roots, when carrots developed 

the large canopy and the extensive 

rooting system. The majority of N is 

taken up during the months of December 

to February, and, hence, proper N 

fertility in the effective crop root zone 

is essential during this period. For a 

160-day crop season, 22% of N uptake 

could be accomplished over the last 30 

days before harvest. 

Carrots have a deep rooting system that 

allows for improved capture of N from 

deep in the soil profile. The fibrous 

roots were present at the depth of five 

feet below the soil surface at site DREC- 

2 (Fig. 7). There is a risk of leaching 

soil residual N due to heavy pre-irrigation 

(a common practice for salinity 

management in the low desert) in late 

summer prior to land preparation. N is 

likely accumulated at the deeper depths 

by the beginning of the growing season, 

and consequently, there is a potential N 

contribution from the soil for carrots 

when the roots are fully developed. 

Since residual soil N contribution can 

be considerable in carrots, pre-plant 

soil nitrate-N assessment down to 60 

cm depth could be a tool enabling 

farmers to improve N management and 

maximize yield and quality while minimizing 

economic and environmental 

costs. 


Careful management of N applications 

in the low desert carrots is crucial 

because fertilizers are the main source 

of N, particularly due to low organic 

matter content of the soils and very 

low nitrate level of the Colorado River 

water. Knowing this fact, the soil 

NO 3 

-N contents pre-seeding and over 

the growing season at different sites 

revealed that none of the sites had N 

deficiency during the crop season, and 

consequently, the practice of splitting 

N applications, as done by the farmers 

(applying 9% to 15% of total seasonal 

N as pre-plant and the remainders 

through irrigation events over the 

season), was likely effective in most 

cases. It appears that the practice of 

15% to 30% seasonal N applications 

though irrigation events 45 to 70 DAS 

has similar effectiveness to sidedress N 

applications. 

Within the range of N application rates 

examined at the experimental sites, 

there were no significant relationships 

between carrot fresh root yield and N 

application rate, although the results 

suggested a positive effect of N application 

on carrot yield. Sufficient N 

availability in the crop root zone over 

the growing season and the lack of 

significant yield response to N applications 

demonstrate that N optimal rates 

could be likely less than the applied 

amounts in most sites. Adequate nitrogen 

and water applications reduce costs 

and help prevent leaching, while excess 

N may lead to excessive N storage in 

the roots, which may be a concern for 

processing carrots. Integrated optimal 

N and water management needs to be 

approached to accomplish greater N 

and water efficiency, and consequently 

keep lower rates beneficial to overall 

profitability. 

Funding for this study was provided 

by California Department of Food and 

Agriculture (CDFA) Fertilizer Research 

and Education Program (FREP) and 

California Fresh Carrots Advisory 

Board. 


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Don’t Let 

Phosphorus 

Erode Away 

How to Improve P Use Efficiency While Protecting Environmental Resources 

By ERYN WINGATE | Agronomist, Tri-Tech Ag Products, Inc. 

Phosphorus (P) availability limited 

food production and human 

population until the Green Revolution. 

After the second World War, 

mineral fertilizers and powerful new 

pesticides drove record yields and exponential 

world population growth. While 

nitrogen fertilizer usually takes all the 

credit, phosphorus is a close second, 

and even the major limiting element 

under some conditions. Mining P-rich 

ore introduced more P to the biosphere 

than ever before. Instead of relying on 

biological P cycling, mineral fertilizer 

now keeps our fields productive 

through years of back-to-back planting. 

P fertilizer provides undeniable improvements 

to yield and crop quality, 

but leaks in the system destabilize surrounding 

ecology, causing a cascade of 

effects that shift global P cycling. With 

fertilizer prices on the rise and environmental 

impact mounting, everyone can 

benefit from improving P management. 

All living organisms require P. It constitutes 

about 9% of our DNA, it is the 

backbone of the phospholipid fatty acids 

giving our cells their structure, and 

P is a critical component of Adenosine 

Triphosphate (ATP), the powerhouse 

of the cell. Plants take up most of their 

P via the roots as the anion phosphate 

Runoff and wind erosion from agricultural fields introduces excess phosphorus and nitrogen to freshwater and marine environments. Nutrient loading 

causes algal blooms and eutrophication, killing off fish and destabilizing the entire ecosystem. 


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). Crops require lots of P early in 

development to support rapidly growing 

cells. P is required at every stage of 

growth, first to support DNA transcription 

and translation, then to build 

the cellular structure and to supply 

energy needed to carry out all the activity. 

Ensuring early access to enough 

plant-available P drives vigorous root 

growth and sets the crop up for success. 

Activity and Availability 

P bioavailability limits many natural 

ecosystems, and plants have evolved 

several ways to gain access to the essential 

element. P is immobile in soil, and 

most of it is tied up in mineral pools 

with very little available as phosphate in 

soil solution. Some P minerals are very 

stable and resist dissolution. Others 

readily dissolve with slight adjustments 

in pH or enzyme activity. Plants and 

fungi take advantage of the labile mineral 

pool by excreting phosphatase and 

lowering the pH in their direct vicinity. 

Mycorrhizal fungi bond with plant 

roots, extending their hyphae far past 

where the plant can reach to bring back 

phosphorus and water in exchange for 

photosynthate. Soil organic matter also 


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available P2O5 in the upper six inches. 

Celery takes up about 100 lbs of 

P2O5 per acre, and about 70% of the 

P is removed from the field with the 

harvested crop. Soils with 100 ppm P 

have 460 lbs P2O5 per acre down to six 

inches, providing more than five times 

the P demand of most vegetable crops. 

Most crops send roots below six inches, 

gaining access to even more P. 

Phosphorus fertilizer gives crops immediate 

access to P, circumventing the 

slower biological cycling. Phosphoric 

acid, monoammonium phosphate and 

other sources initially spike soil solution 

phosphate, but the effect does not 

last. In calcareous and high-pH soils, P 

eventually disappears from the plant 

available pool as it binds with calcium 

to form the mineral apatite. Under 

acidic conditions, phosphate precipitates 

with iron and aluminum hydroxides. 

The P fixation rate depends on 

many factors, including pH, temperature, 

moisture and the concentration 

of other compounds in soil solution. 

Growers apply more P fertilizer every 

year to meet immediate crop needs, 

even though total soil P levels continue 

rising. 

Likelihood of crop response to phosphorus fertilizer (adapted from Geisseler, 

Daniel. (2015). California Fertilization Guidelines. Fertilizer Research and Education 

Program. http://geisseler.ucdavis.edu/Guidelines/Home.html.) 


stores P, and microbial activity releases 

phosphate into solution according to 

population dynamics and access to 

carbon and nutrients. 

Most P fertilizer recommendations are 

based on observed crop response to 

fertilization at different soil P concentrations. 

Many studies in the western 

region show that crop yield and quality 

increases when fertilizer is applied to 

soil with less than 40 ppm P measured 

by the Olsen test. Soil containing 40 

ppm P holds roughly 180 lbs plant 

Environmental Impacts 

While adsorbed P might not be accessible 

to the crop, the extra nutrition 

disproportionately impacts freshwater 

and marine environments when it 

escapes the farm via runoff or wind 

erosion. Relatively small increases in 

P concentration in lakes, streams and 

ocean water cause major ecological 

shifts. High N and P levels induce eutrophication 

by triggering algal blooms 

that block sunlight from penetrating 

the water’s surface layer. Unable to 

photosynthesize, aquatic plants die 

and sink to the bottom, introducing an 

overabundant food supply to microorganisms. 

Aerobic metabolism depletes 

the water’s oxygen concentration as 

microbes decompose the plant material. 

Oxygen diffusion down to lower depths 

can’t keep pace with the consumption 

rate. Hypoxic zones drive away or kill 

off fish, and the aquatic ecosystem 

unravels, leading to permanent dead 


zones under the worst conditions. 

Researchers point to organic matter 

as the solution to almost every soil 

quality challenge, and phosphorus is 

no exception. Increasing soil organic 

matter and microbial activity helps 

prevent erosion and increases the 

bioavailability of P already in the soil. 

Microbial metabolism releases carbon 

dioxide, dissolving calcium phosphate 

minerals. Enzymes and organic acids 

also liberate phosphate, while mycorrhizal 

networks mine phosphorus from 

parts of the soil profile that plant roots 

cannot reach. Meanwhile, microbial 

activity and organic matter build soil 

structure, forming stable aggregates 

that resist erosion from water and 

wind. One major windstorm can blow 

away an inch of topsoil carrying away 

valuable phosphate fertilizer. Soil with 

100 ppm P concentration holds almost 

80 pounds of plant-available phosphate 

in the upper inch of soil. Many fields 

have accumulated P to well over 200 

ppm, doubling or tripling the cost of 

eroded P. 

Phosphorus fertilizer is a valuable 

‘While a heavy P 

application may 

have significantly 

increased yield 

the first couple 

of years, continued 

applications 

at the same rate 

may have little 

effect.’ 

tool and a mainstay of almost every 

fertilizer regimen. Increased yields 

and reasonably priced fertilizer keep 

growers applying mineral P every 

season. While a heavy P application 

may have significantly increased yield 

the first couple of years, continued 

applications at the same rate may have 

little effect. Soil tests can help determine 

baseline P content and the soil’s 

adsorption capacity. Water quality, soil 

pH and calcium content affect how 

quickly P fertilizer precipitates out of 

the plant-available pool. Management 

practices like splitting P into several 

applications or applying it with an 

organic amendment can help keep a 

steady supply of P in plant-available 

form. Like most agricultural challenges, 

the best solutions are multipronged, 

with many little adjustments adding up 

to dramatically improve the big picture. 

Better P management will protect our 

freshwater and marine environments, 

enhance crop quality and even save 

growers some money. 

References 

Brady, Nile C. and Weil, Ray R. (2008). 

The Nature and Properties of Soils. Fourteenth 

Edition. Pearson Prentice Hall. 

Filippelli, Gabriel. (2008). The Global 

Phosphorus Cycle: Past, Present, and 

Future. Elements. 4. 89-95. 10.2113/ 

GSELEMENTS.4.2.89. 

Geisseler, Daniel. (2015). California Fertilization 

Guidelines. Fertilizer Research 

and Education Program. http://geisseler. 

ucdavis.edu/Guidelines/Home.html 

Liu, Guodong, Li, yuncong, & Gazula, 

Aparna. (2019). Conversion of Parts Per 

Million on Soil Test Reports to Pounds 

Per Acre. University of Florida Extension. 

https://edis.ifas.ufl.edu/publication/hs1229 

Wyant, Karl A., Corman, Jessica R., & 

Elser, James J. (Eds.). (2013). Phosphorus, 

Food, and our Future. Oxford 

University Press. 




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Ongoing University of California Hemp 

Research to Address Water, N issues 

By JEANNETTE E. WARNERT | Communications Specialist, UC ANR 

UCCE and UC Davis research efforts to understand the opportunities and 

challenges for industrial hemp production in California are growing. 

As a crop relatively new to California growers and researchers, there is still 

much to learn about variety choices, how varieties and crop responses differ 

across regions with different soils and climates, best practices for nutrient management, 

and pest and disease issues. 

Industrial hemp field research efforts began at the University in 2019 after the 

previous year’s Farm Bill declared the crop should no longer be considered a 

controlled substance, but rather an agricultural commodity. Hemp is valued for 

its fiber and edible seeds; however, in California, producing hemp primarily for 

essential oils, including medicinal cannabidiol (CBD), is thought to offer the best 

economic outlook. U.S. and California hemp acreage surged in 2019, but fell in 

2020. 

Hemp Water-Use Study Expands 

In a study coordinated by Jeff Steiner of Oregon State University’s (OSU) Global 

Hemp Innovation Center, drip irrigation trials are underway in California, Oregon 

and Colorado. Research was conducted in 2020 at the UC West Side Research 

and Extension Center in Five Points and at the UC Davis campus in addition to 

three sites in Oregon, with an additional site in Colorado added in 2021. These 

studies were set up to determine water use of industrial hemp for CBD production 

under irrigation regimes ranging from about 40% to 100% of estimated crop water 

requirements, with comparisons of responses observed across the five sites with 

different soils, climate and other environmental conditions. 

The study, funded by USDA and OSU, includes photoperiod-sensitive cultivars, 

where the flowering response is triggered by shortening day lengths in mid- to 

late summer in central California, and auto-flower varieties that do not require 

shortening day length to flower. 

Some of the irrigation treatments impose moderate to more severe deficit irrigation 

to help assess the crop responses to water stress. Deficit irrigation is a method 

of conserving water by applying less than what might be considered optimum for 

maintaining rapid growth. 

Researchers found that hemp appears to be 

tough under deficit irrigation, a method of 

conserving water by applying less than what 

might be considered optimum for maintaining 

rapid growth (all photos courtesy B. Hutmacher.) 

“This plant appears to be quite tough under deficit irrigation,” said UCCE Specialist 

Bob Hutmacher at the UC WSREC. 

“We need to learn more about benefits and drawbacks to stressing the plants,” 

Hutmacher said. 



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The auto-flower cultivars tested tend 

to use less water than the photoperiod-sensitive 

cultivars because they can 

be grown in a shorter season. In the San 

Joaquin Valley, auto-flower cultivars in 

these studies were ready for harvest in 

75 to 90 days after seeding. 

“Water use is very variety-specific” Hutmacher 

said. “Auto-flower varieties may 

have potential to be grown in the spring 

and harvested by early summer, or 

planted in late summer and harvested 

before winter. With a short-season crop, 

and with a decent water supply, farmers 

could consider double-cropping with 

such varieties, potentially increasing 

profits.” 

Yields were variable, but showed promise 

for auto-flower varieties. 

“In our studies, the highest-yielding 

auto-flower cultivars have produced 

80% to 90% of yields of the much larger 

full-season, photoperiod-sensitive 

plants, and some varieties may be equal,” 

he said. 

Hemp Planting Density Studies 

In cooperation with Kayagene Company 

of Salinas, Dan Putnam, UCCE 

forage crops specialist at UC Davis, and 

Hutmacher have conducted studies 

in 2019 and 2020 with two auto-flower 

varieties to determine the effect of 

plant density on crop growth, yield and 

chemical concentrations. Since some of 

the auto-flower varieties are smaller and 

earlier maturing than many photoperiod-sensitive 

cultivars, data in these 

studies will help determine the tradeoff 

between higher densities needed to increase 

yields versus increases in the cost 

of higher seeding rates. 

A key concern for growers is producing 

a crop with economic levels of CBD 

or other compounds of commercial 

interest, while staying within regulatory 

limits for THC (tetrahydrocannabinol), 

the psychoactive compound found in 

marijuana, a related plant. According to 

CDFA, an industrial hemp crop grown 

in the state may have no more than 0.3% 

THC when plant samples are analyzed. 

“This is a challenge for growers. You 

don’t want to risk too high a THC 

level,” Hutmacher said. “Farmers must 

test to make sure THC is at a level to 

meet regulations. If it’s too high, CDFA 

regulations would require the crop be 

destroyed.” 

The studies provide opportunities for 

the scientists to assess plant-to-plant 

variation and impacts of flower bud position 

on THC and CBD concentrations. 

The data collected across a range of 

cultivars differing in plant growth habit 

may help better inform both researchers 

and regulatory groups in decisions regarding 

how to monitor plant chemical 

composition. 

Hutmacher and Putnam are also working 

with commercial companies to test 

lines in the field, including Arcadia 

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Biosciences in Davis, Phylos Biosciences 

in Portland and Front Range Biosciences 

in Salinas. 

“There are a lot of challenges when it 

comes to estimating maturity with 

these varieties,” Putnam said. “Each 

variety will mature at different times, 

and deciding when is the best time is a 

key decision. We’re still learning about 

this issue” 

In 2021, in variety trials also coordinated 

by OSU’s Global Hemp Initiative 

Center, data will be collected from studies 

at up to 12 locations ranging from 

Oregon, Washington and California 

in the West to New York, Vermont and 

Kentucky in the eastern U.S. to compare 

varieties grown for CBD and other 

essential oils. 

“Our participation in these multi-site 

trials is important in efforts to identify 

across very diverse environments and 

latitudes the plant response in terms of 

attained levels of CBD and THC,” Hutmacher 

said. 

Launch of Hemp Fertilizer 

Project in 2021 

As a new crop in California, little is 

known about crop nitrogen needs 

and application optimization to 

prevent environmental problems 

related to overuse. In 2021, a 

team of UC Davis researchers are 

launching a three-year nitrogen 

management trial supported by the 

CDFA Fertilizer Research Education 

Program (FREP). An important 

part of the project is THC and 

CBD analysis, a costly enterprise. 

Three companies are providing seeds or 

clones for the project: Cultivaris Hemp 

of Encinitas, Kayagene of Salinas and 

Phylos Biosciences of Portland. Alkemist 

Labs of Garden Grove is donating 

services for analyzing crop samples. 

“These are incredibly valuable donations 

to assist with this project, certainly in 

excess of $50,000 in donated materials 

Another study is using data from 2019 and 2020 to 

help determine the tradeoff between higher densities 

needed to increase yields versus increases in the cost of 

higher seeding rates. 

and services from each of those companies,” 

Hutmacher said. The collaboration 

with the donors makes the 

development of environmentally sound 

nitrogen optimization information 

for growers possible together with the 

money provided by CDFA-FREP for the 

trials. 


to hear from you. Feel free to email us 

at article@jcsmarketinginc.com 



Activator Spray Adjuvant 

Selection in Trees and Vines 

By FRANZ NIEDERHOLZER | UCCE Farm Advisor, Colusa and Sutter/Yuba Counties 

and RHONDA SMITH | UCCE Farm Advisor, Sonoma County 

If the label includes phrases such as “use of an adjuvant may improve results” or “complete coverage is needed for best results,” then you 

may want to look into selecting and using an appropriate activator adjuvant (photo courtesy F. Niederholzer.) 

Agricultural spray adjuvants are 

materials added to the spray tank 

when loading the sprayer. They 

include products classified as activator 

adjuvants and marketed as wetters/ 

spreaders, stickers, humectants and/ 

or penetrators. Activator adjuvants are 

marketed to improve the performance 

of pesticides and foliar fertilizers. 

Activator adjuvants can have a place in 

tree and vine crop sprays, but matching 

the material to the job can be tricky. A 

bad match can lead to minor or major 

losses to the grower. Minor losses 

can result from excess spreading and 

pesticide runoff from the target plant. 

Phytotoxicity can cause major damage. 

This article describes ingredients 

and functions of activator adjuvants 

commonly sprayed on tree and vine 

crops. Suggestions regarding activator 

adjuvant selection are offered. Growers 

must make their own activator adjuvant 

use decisions based on experience, 

particular needs and risk tolerance. 

When to Use an Activator Adjuvant 

Read and follow the specific instructions 

on the label. If the pesticide 

or foliar fertilizer label indicates the 

product should be used with a certain 

type or brand of adjuvant(s), that’s what 

you need to use. For example, the Bravo 

Weather stik ® label cautions against 

using specific adjuvants and puts the 

responsibility on PCA or grower court 

regarding adjuvant use. 

If the label includes phrases such as 

“use of an adjuvant may improve results” 

or “complete coverage is needed for 

best results,” then you may want to look 

into selecting and using an appropriate 

activator adjuvant. 

Before proceeding with use of an 

activator adjuvant, first look at your 

existing spray program. Are you 

already doing the best spray job you 

can? Good spray coverage begins with 

proper sprayer calibration and setup. 

Is your sprayer calibration dialed in 

for different stages of canopy development? 

Optimum sprayer setup (gallons 

of spray per acre, ground speed, fan 

output and nozzle selection/arrangement) 

changes from dormant to bloom 

to early growing season to preharvest 

sprays. Adjusting your sprayer to best 

match orchard and vineyard conditions 

at each general stage in canopy 

development is the foundation of an 

effective, efficient spray program. An 

activator adjuvant will not make up for 

excessive tractor speed, poor nozzle 

arrangement and/or worn nozzles. Your 

money is best spent first dialing in your 

sprayer(s) for the whole season before 

considering an extra material in the 

tank that is not required on the label. 

If you have your sprayer(s) dialed in for 

each orchard and stage of growth, now 



is the time to say, “OK, I want to 

think about a little extra boost to 

my spray job.” 

® 

Which Activator Adjuvant to Use 

First, know the properties of the 

pesticide you will use. Does it work 

on the plant surface or inside the 

plant? This is a key point in selecting 

adjuvants. Here is a quick 

review of the main classifications 

and characteristics of activator 

adjuvants as they currently appear 

in the field. Note: Certain products 

can provide more than one adjuvant 

property; that can be beneficial in 

the field. For example, non-ionic 

surfactants can work as surfactants 

and penetrators, depending on use 

rate. 

Wetters/Spreaders 

These materials contain surfactants 

that decrease the contact angle and 

increase the spreading of the spray 

droplet on the target. High rates of 

wetters/spreaders may also increase 

penetration of pesticides into 

the target tissue (leaves or fruit), 

potentially causing phytotoxicity. 

Excessive spreading of pesticide 

spray solution and runoff from the 

target may result when using a new 

or higher rate of spreader, especially 

when using silicon “super-spreaders”. 

Test new combinations of 

spreader material(s) and spray 

volume before regular use. Spray 

volume per acre or adjuvant use rate 

will probably have to be reduced if 

a labeled rate of adjuvant provides 

excessive spreading. 

To check for excessive spreading, 

place a length of black plastic sheeting 

under several trees or vines in a 

row. Secure the plastic with spikes, 

wire staples and/or weights. Spray 

the new adjuvant and pesticide 

combination using your current 

sprayer setup. Reenter the field right 

after spraying, wearing appropriate 

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PPE, and evaluate coverage. If material 

is pooling at the lower portion of leaves 

and/or fruit, excessive spreading is 

occurring. Check to see if pooling is 

occurring only in a certain area(s) of 

the canopy or throughout the canopy. 

If more spray solution is landing on the 

black plastic tarp under the trees/vines 

than between them, then runoff is 

occurring. Some ground deposit should 

be expected from standard airblast 

sprayer use. 

Compare the results of your adjuvant 

test with a similar application of your 

current pesticide/adjuvant combination 

on another portion of the row. If 

there is no pooling or runoff with the 

new adjuvant in the tank, you can use 

the adjuvant with confidence. A lack 

of pooling or run off with the new 

adjuvant also might mean that your 

old sprayer setup and tank mix didn’t 

'Products that are advertised for use 

with plant growth regulators should 

have a higher chance of crop safety 

compared with those that don’t.’ 

deliver adequate coverage. 

If the test with the new adjuvant 

showed pooling on leaves and/or runoff 

on the ground, you have several choices: 

1) You can reduce spray volume per 

acre by replacing some or all nozzles 

with smaller nozzle sizes on the sprayer 

in an effort to reduce overspreading. 

If you saw overspreading on some 

portions of the canopy but not others, 

reduce nozzle size only on the part of 

the spray boom that targets the oversprayed 

part of the canopy. Recheck 

spray coverage if nozzling changes were 

made. 2) Reduce the adjuvant rate and 

recheck coverage/spreading. 3) You can 

go back to your established program 

without the new adjuvant. 

What’s the “best” course of action? That 

depends on your farming operation. 

Reducing spray volume per acre means 

more ground covered per full spray 

tank, a potential time and cost savings. 

If spraying is done during the heat of 

the day in hot, dry climate, spray water 

evaporation is a major issue, and it may 

be best to keep the higher spray volume 

and reduce the spreader rate or eliminate 

it entirely. Checking coverage and 

overspreading allows you to make the 

best decision possible; avoid damage 

and, hopefully, save money. All farm- 

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ing operations are different. Make the 

choice that best fits your farm. 

Stickers 

These adjuvants can increase the 

retention time of the pesticide on the 

leaf and reduce rain wash-off. They may 

limit movement of systemic pesticides 

into the plant and are probably most 

beneficial when used with protectant 

materials (cover sprays). Do you 

overhead irrigate? Is there rain on the 

horizon? If you answer yes to either 

one of these questions, you may benefit 

from using a sticker. 

Humectants 

Under low humidity conditions, humectants 

can help reduce spray droplet 

evaporation before and after deposition 

on the plant. This is especially valuable 

when small droplets and/or materials 

that must be absorbed into the plant 

(systemic pesticides, PGRs, nutrients, 

etc.) are used in the summer under 

high temperature and low relative humidity 

conditions. 

Penetrators 

Frequently used with herbicides, these 

products include oils (petroleum, vegetable 

or modified vegetable oils) and 

non-ionic surfactants used at higher 

rates. In crop sprays, penetrators can be 

used to increase absorption of systemic 

pesticides (e.g., oil with Agri-Mek) as 

well as translaminar materials. Penetrator 

adjuvants should be used with 

caution or avoided entirely with surface 

active pesticides such as cover sprays or 

else phytotoxicity may result. Finally, 

some penetrators can increase the 

rain-fastness of some pesticides. 

Do Your Homework 

Use a product intended for crop spraying. 

Many activator adjuvants were 

developed and intended for use with 

herbicides. Products that are advertised 

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for use with plant growth regulators 

should have a higher chance of crop 

safety compared with those that don’t. 

This is still no guarantee of a phytotoxicity-free 

application. 

If you choose to use an adjuvant that is 

not specifically listed on the pesticide 

or foliar fertilizer label, jar test the 

planned spray solution first. Use the 

same spray water source. Include all 

leaf feeds, other adjuvants and pesticide(s) 

that you plan to put in the spray 

tank. Do this before tank mixing these 

materials. 

A lot of time and money rides on 

effective pesticide application. Do your 

homework before the spray tank is 

filled and you will be well on your way 

to solid results. 




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LODI RULES for Sustainable 

Winegrowing: A Quality 

Winegrape Program 

By CLIFFORD P. OHMART, PH.D. | Ohmart Consulting Services 

The LODI RULES is organized into six chapters: Business Management, 

Human Resources Management, Ecosystem Management, 

Soil Management, Water Management and Pest Management. 

No tillage and maintenance of a cover crop every vine row gets 

the most practice points because these practices promote soil 

health through better drainage, increased organic matter content, 

increased soil moisture holding capacity and better soil microbial 

activity (all photos courtesy Lodi Winegrowers Workbook 2nd 

edition 2008. Ohmart, C. P., Storm C. P. and Matthiasson, S. K. eds. 

345pp.) 

To achieve certification, a vineyard must be farmed using practices 

that score 50% or more of the total possible points in each LODI 

RULES chapter and 70% of the points in the six chapters combined. 

What are the Lodi Rules for Sustainable Winegrowing 

(LODI RULES), which entered its 16 th year in 

2021? It is a set of farming practices that result in 

higher quality winegrapes and wine according to grower and 

winemaker panelists on a recent webinar entitled ‘Boots on 

the Ground – A masterclass in sustainable viticulture & LODI 

RULES,’ a collaboration of the SommFoundation and the Lodi 

Winegrape Commission and hosted by Elaine Chukan Brown. 

On a technical level, LODI RULES is California’s first 

third-party certified sustainable winegrape-growing program. 

It was initially developed for growers in Lodi’s Crush District 

#11 but made available to any California winegrape grower in 

2008, expanded to Israel (Golan Heights Winery) in 2017 and 

Washington State winegrape growers in 2020. LODI RULES 

encompasses more than 120 farming practices, some of which 

will be discussed in this article, and is certified by Protected 

Harvest, a non-profit third-party certifier of sustainable farming 

programs. 

Origins of LODI RULES 

From 2003 to 2004, I led the team of 22 winegrape growers, 

Lodi Winegrape Commission staff, crop consultants, PCAs, 

UC Farm Advisors, a wildlife biologist and a winemaker to 

create the first edition of the LODI RULES farming standards. 

They were based on what the team considered to be the 

most sustainable farming practices in the Lodi Winegrowers 

Workbook (Ohmart and Matthiasson 2000.) They were then 

submitted to Protected Harvest for scientific peer review and 

endorsed in 2005. The LODI RULES farming standards have 

been updated twice since then. The program has grown from 

six growers and 1200 vineyard acres in 2005 to more than 130 




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growers and 68,000 acres participating 

in 2021. In 2008, one winery started 

paying bonuses for LODI RULES 

certified grapes, and since then, many 

others have followed suit. One estimate 

has the annual bonuses exceeding $2 

million. 

The LODI RULES is organized into 

six chapters: Business Management, 

Human Resources Management, Ecosystem 

Management, Soil Management, 

Water Management and Pest Management. 

Each farming practice standard 

is assigned a number of points based on 

its assessed level of importance in sustainable 

winegrowing. To achieve certification, 

a vineyard must be farmed 

using practices that score 50% or more 

of the total possible points in each 

chapter and 70% of the points in the six 

chapters combined. The purpose of this 

scoring is so that a vineyard does not 

obtain certification while performing 

poorly in one chapter but very high in 

all the others. Furthermore, pesticides 

used in the vineyard are run through a 

pesticide risk model that calculates risk 

points for each application. To achieve 

ensures all growers 

are up to date 

with their records 

and practices. The 

auditors submit 

their reports to 

Protected Harvest 

near harvest for 

final certification 

decisions. 

I will now highlight 

a few of the 

practices in each of 

the LODI RULES 

chapters. I will 

remind you that 

there are more 

than 120 practice 

standards, so I am 

only able to touch 

on a few of them. For a complete copy 

of the LODI RULES farming standards, 

go to lodigrowers.com in the grower 

resources section. A farming practice 

standard is a description of a practice 

that is required to be done in order 

to qualify for the points awarded for 

doing the practice. It is very specific 

and is described in a way that enables 

an auditor to clearly verify the practice 

The farming practice standards for ecosystem management focus 

primarily on parts of the farm that are outside the vineyard, such 

as riparian areas like the one seen here. 

One might ask, ‘Why is having a sustainable 

management vision plan for 

the farm so important?’ I will answer 

this question by quoting one of my 

favorite Yogi Berra statements: “If you 

don’t know where you are going, you 

may end up some place else!” Sustainable 

winegrowing is a long-term commitment 

and needs long-term goals so 

one has a target to aim for. 

“If you don’t know where 

you are going, you may 

end up some place else!” 

certification, the risk points from the 

year’s pesticide applications cannot 

exceed a rigorous risk points threshold. 

Independent professional auditors are 

contracted by Protected Harvest to 

audit annually the practices being used 

in each participating vineyard. An onsite 

audit is done on any vineyard new 

to the program and at least every three 

years after that. A desk audit is done 

each year for every vineyard not visited 

on-site. And finally, a grower is chosen 

at random each year for an audit to 

be done with a 48-hour notice. This 

-Yogi Berra 

is being done during the onsite audit of 

the vineyard being certified. 

Business Management 

The very first farming practice standard 

in LODI RULES is the requirement that 

a grower attend a LODI RULES workshop 

sponsored by the Lodi Winegrape 

Commission where they learn how to 

develop a sustainable management 

vision plan for their farm. They then 

need to draft the plan that contains 

elements that they were introduced to 

in the workshop. 

Other important practices in the chapter 

are developing plans for leadership 

succession within the farming enterprise 

and business risk management as 

well as tracking fuel and electricity use 

following the adage if you can’t measure 

it, you can’t manage it. 

Human Resources Management 

The first practice standard in the chapter 

is to develop a human resources 

management plan for the farm. Other 

practice standards relate to team building, 

employee training and development, 

employee performance evaluation, 

employee orientation, providing 

health care and benefits, safety training 

and a safety rewards program. 

Ecosystem Management 

The farming practice standards for ecosystem 

management focus primarily on 

parts of the farm that are outside the 

vineyard. They start with an environ- 



Many wineries now require sustainability certification of their 

growers. 

mental survey to identify and document 

important environmental features 

such as swales, riparian areas, trees, 

woodlands or vernal pools whose presence 

would impact how the farming is 

done in the vineyard. 

This is followed by 

the development 

of an Ecosystem 

Management plan 

for the farm. Then 

there is a series of 

detailed farming 

practice standards 

for managing 

important ecosystem 

elements from 

cover crops in the 

vineyard, vegetation 

adjacent to the 

vineyard, and, if 

present, managing 

woodlands, individual 

trees, seasonal 

wetlands or riparian 

habitat. 

There are other practice standards 

focused on biodiversity and providing 

nesting boxes for owls, birds and bats. 

And finally, if a grower has grazing animals 

on the farming, a grazing management 

plan needs to be developed 

and implemented. 

Soil Management 

The soil management chapter starts 

with farming practice standards for developing 

and implementing a nutrient 

management plan based on vine needs 

over the season, a soil conservation 

plan to minimize erosion due to wind 

and water and a soil map confirmed 

by soil coring or a soil pit. No tillage 

and maintenance of a cover crop every 

vine row gets the most practice points 

because these practices promote soil 

health through better drainage, increased 

organic matter content, increased 

soil moisture holding capacity 

and better soil microbial activity. 

Soil and vine tissue sampling is 


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required to be done to monitor the 

nutrient availability and status in vine 

tissue so as to guide nutrient additions 

if they are determined to be necessary. 

Several farming practice standards 

address nitrogen management due to 

its importance in vine performance as 

well as its mobility in the soil, making 

it prone to leaching into the ground 

water during winter rains. 

Water Management 

Water management is a critical element 

of sustainable winegrowing because it 

is a precious resource in California as 

well as the recognized fact that irrigation 

management is one of the most 

important ways to influence winegrape 

quality and therefore wine quality. The 

chapter starts with a practice standard 

for the development and implementation 

of a water management plan that 

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states goals and strategies, followed by 

a focus on soil water holding capacity, 

water intake rate and permeability, and 

irrigation system design and performance 

measuring and monitoring. 

Due to the importance of a properly 

performing irrigation system, several 

standards focus on amount of water 

used, maintenance, distribution uniformity 

and pump efficiency, with practices 

specific to micro, sprinkler or flood 

systems. There are also practice standards 

for irrigation scheduling based 

on monitoring vine water demand, 

level of soil moisture and avoidance of 

offsite movement of irrigation water. 

Pest Management 

I have long felt that pest management 

is one of the most challenging areas of 

sustainable winegrowing to capture 

in a set of farming practice standards. 

That is because, ideally, pest problems 

in the vineyard are 

minimal due to 

the grower having 

A foliar spray that creates a 

semi-permeable membrane 

over the plant surface. 

implemented a 

whole range of preventative 

practices 

that preclude the 

development of pest 

problems. In other 

words, much is 

done to minimize 

the need for a pest 

control action. Many of these preventative 

practices are captured in farming 

practice standards in other LODI 

RULES chapters such as Water, Soil and 

Ecosystem Management. 

The Pest Management chapter begins 

with a standard for development and 

implementation of an insect and mite 

management plan. It is followed by one 

for insect and mite population monitoring 

and data recording and another 

specifying economic thresholds for 

management actions against leafhoppers 

and mites. 

There are several practice standards for 

disease management due to its importance 

in developing an economically 

acceptable yield, quality winegrapes 

and ensuring the maximum length of 

life for the vineyard. The first is the 

development and implementation of 

a Powdery Mildew management plan 

given the key role this disease plays 

in vineyard management. There are 

practice standards for when to initiate 

mildew treatments in the early stages 

of the growing season, the subsequent 

timing of treatments as the season 

develops as well as one for managing 

fungicide resistance. There are also 

practice standards for managing Botrytis 

and canker diseases. 

Weed and vertebrate pest manage- 

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Sustainable farming practices within and outside of the vineyard 

are assigned a set of points under the LODI RULES program. 



ment are addressed through standards 

requiring the development and implementation 

of weed and vertebrate pest 

management plans followed by ones for 

monitoring and recording their respective 

populations. 

When a pest problem needs an action, it 

is often in the form of spraying, whether 

it is due to an insect, mite, disease or 

weed. We all appreciate the importance 

of sprayer calibration and maintenance, 

but it is often challenging for many 

growers to do them in a timely manner. 

Therefore, there are practice standards 

that thoroughly address these two critical 

aspects of pest management. 

Pest problems change through time and 

it is important that the LODI RULES 

keep up with them. New practice 

standards are periodically added when 

revisions to the program are made. For 

example, given the rapid rise in the 

importance of leaf roll and red blotch 

viruses and the vectoring of some of 

them by Vine Mealybug, new sustainable 

practice standards have been 

written to address this issue and will be 

added to the program in 2022. 

pilot is required to do before flying 

their plane. They go through a checklist 

of all the different systems on the 

plane to ensure they are in working 

order. Many of the things are obvious, 

but there are so many that it is easy to 

overlook some of them in day-to-day 

flying. The checklist assures that does 

not happen. As passengers on the plane, 

we can appreciate the importance of 

going through this check list! The same 

can be said for sustainable viticulture. 

® 

There are so many practices involved in 

growing winegrapes sustainably. Many 

are obvious and are second nature to a 

grower. However, it is easy to overlook 

some in the day-to-day frenzy involved 

in farming. Certifying to the LODI 

RULES ensures this does not happen. 




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I often hear growers say, ‘Of course I 

farm my vineyard sustainably, why do I 

need to be certified?’ One reason is that 

more and more wineries are requiring 

certification to obtain and maintain a 

winery contract. That, however, is a cost 

of doing business requirement, which is 

not something that is all that inspiring 

for a grower. 

Two primary goals for the team that 

created the LODI RULES was that 

implementing them would result in 

higher-quality winegrapes and help a 

grower improve their farming operation. 

Based on the feedback from growers 

in the program and wineries that 

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Nitrogen Fertilization Alters 

Phosphorus Status of Grapevines 

and Their Association with 

Arbuscular Mycorrhizal Fungi 

By TIAN TIAN | UCCE Area Viticulture Farm Advisor, Kern County 

Maintaining AMF colonization in grapevine roots is particularly 

important for vineyards in Oregon’s Willamette Valley where red-hill 

soils are most commonly found. 

Nitrogen (N) is one of the most 

managed nutrients in vineyards, 

since it strongly affects vine 

growth and fruit development. Although 

numerous studies have been 

conducted to understand how N fertilization 

influences vine productivity and 

fruit composition, the impacts of N on 

vine nutrient status and soil microbes 

receive less attention. 

Among a wide range of soil microbes 

that play vital roles in soil health and 

vine productivity, arbuscular mycorrhizal 

fungi (AMF) are unique due to their 

symbiotic association with grapevines 

and their contribution to vine nutrient 

acquisition. Arbuscular mycorrhizal 

fungi obtain nutrients from the soil, 

especially for phosphorus (P) and other 

poorly mobile nutrients, and transfer 

those nutrients to the plant. In turn, 

plants provide sucrose and fatty acids 

to AMF to support fungal functions 

and growth. 

To sustain intensive nutrient exchange 

between two partners, AMF colonize 

individual cortical cells of fine 

roots and form arbuscules, which are 

tree-like fungal structures that greatly 

increase surface area contact between 

plants and AMF (Fig. 1, see page 34). 

Grapevines are considered a “super” 

host of AMF. The percentage of fine 

roots colonized by AMF is generally 

above 60% in field and greenhouse conditions. 

Such high colonization rates 

also reflect the great dependency of 

grapevines on AMF. Indeed, non-mycorrhizal 

vines are stunted in low P 

soils, while mycorrhizal vines could 

acquire adequate P from the soil, overcome 

P limitation and grow normally. 

Willamette Valley Trials 

Maintaining AMF colonization in 

grapevine roots is particularly important 

for vineyards in Oregon’s Willamette 

Valley where red-hill soils are 

most commonly found. Since those 

highly weathered acid soils have low P 

availability, grapevines rely on AMF for 

ample P acquisition. In other crops, N 

fertilization was shown to reduce root 

colonization by AMF, but it is unclear 

whether N applied at moderate rates 

would decrease mycorrhizal colonization 

in grapevines. If N applications 

would suppress AMF and impair vine 

P uptake, this negative effect should 

be accounted for when developing 

fertilization management plans for 

vineyards. This article summarizes part 

of my Ph.D. research conducted in Oregon, 

which explored how vineyard N 

applications affect vine nutrient status, 

root growth and AMF. 

Experiments were conducted in a 

Chardonnay vineyard and a Pinot noir 

vineyard over three years in Willamette 

Valley. Both vineyards are somewhat 

limited by N but have varying levels of 

soil P. At each site, we evaluated three 

treatments, including no N application 

(No N), N applied to the soil (soil N) 

and N applied to the foliage (foliar N). 



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Figure 1: Grapevine roots colonized by arbuscular mycorrhizal fungi 

(AMF). Red arrow indicates arbuscules, “tree-like” structures that 

vastly increase surface area contact between the host plant and the 

fungus (photo courtesy Dr. R. Paul Schreiner, USDA-ARS.) 


Each treatment was replicated four times. The soil N vines 

were fertilized two or three times between bud break and 

veraison using UAN-32 at the rate of 40 to 60 lbs N/acre/year. 

The foliar N vines received three urea sprays to the canopy 

from fruit set to two weeks post veraison at the rate of 19 to 

23 lbs N/acre/year. 

All treatments were evaluated across three years in both 

vineyards with the exception that foliar N treatment was 

assessed only in Year 2 and 3 in Chardonnay. In each season, 

leaf blades and petioles were sampled at bloom and veraison 

for nutrient analysis. Due to the late initiation of foliar N 

treatment in Chardonnay, bloom leaf samples were collected 

only in Year 3 for this specific treatment. Soils and roots 

were sampled three times a year when berries were pea-size, 

near veraison and about a month after harvest. 

Effects of Soil N Applications in Chardonnay 

As expected, soil N applications increased vine N status 

starting from Year 1 (Fig. 2). For simplicity, only petiole 

nutrient data at bloom are presented here. Changes of nutrients 

in corresponding leaf blades followed a similar trend. 

Previous work on Pinot noir in the Willamette Valley proposed 

0.7% as the critical value of petiole N concentration at 

bloom to ensure sufficient yield (2.5 to 3.5 U.S. ton/acre) and 

adequate fruit N. 

Figure 2: Effect of nitrogen (N) applications to the soil and the foliage (soil 

N and foliar N) on petiole N and phosphorus (P) concentration at bloom 

in Chardonnay. Vines that received no N application (no N) served as the 

control. Means followed by different letters indicate significant differences 

between treatments in each experimental year based on a t-test or Tukey 

HSD test at 95% confidence. 

Since Chardonnay vines in this region generally carry heavier 

crop load (four to five U.S. ton/acre) and develop larger 

canopies compared to Pinot noir vines, Chardonnay vines 

may have a higher N requirement. With a petiole N concentration 

of 0.6% at bloom, Chardonnay vines that received no 

N applications clearly experienced some N limitation in this 

study. Soil N applications improved bloom petiole N concentration 

by 15% to 30%. In response to greater vine N status, 

the soil N vines had 30% higher yield and about 35% more 

pruning mass as compared to the no N vines. 

Soil N applications decreased vine P status in Chardonnay 

in Year 2 and 3, where petiole P concentration at bloom was 

about 30% lower in the soil N vines than no N vines (Fig. 

2). The negative effect of soil N fertilization on vine P status 

became more evident in late season. The concentration of 

petiole P at veraison decreased 50% in the soil N vines in the 

last two years of the experiment. 


Table 1: Effects of N applications to the soil 

and foliage (soil N and foliar N) on root density 

and colonized by arbuscular mycorrhizal fungi 

(AMF) in Chardonnay. Vines that received no 

N application (no N) served as the control. 

Means followed by different letters indicate 

significant difference between treatments in 

each experimental year based on a Tukey HSD 

test at 95% confidence. 

YEAR 2 

YEAR 3 

YEAR 3 

Total Root Length 

Treatments % AMF %Arbuscules 

(mm/g dry soil) 


No N t 

Soil N 

Foliar N 

No N 

Soil N 

5.5 b 

8.0 a 

5.6 b 

5.5 b 

8.7 a 

91.3 a 

80.8 b 

90.8 a 

94.0 a 

90.6 b 

46.6 a 

35.8 b 

45.3 a 

37.5 

30.8 

Foliar N 

6.3 ab 

94.3 a 

33.7 

Why did soil N applications reduce 

vine P status? The most straightforward 

answer would be the dilution of 

P in leaves due to N stimulated canopy 

growth. However, this is unlikely 

the sole reason. Soil N applications 

increased veraison leaf area by 10% 

to 19% in Year 2 and 3, while the 

corresponding leaf blade P decreased 

to a larger extent (19% to 29%). The 

second possible explanation for the 

decreased leaf P under increased soil 

N supply is that fertilization altered P 

allocation within the plant and less P 

was translated above ground. Indeed, 

because soil N fertilization increased 

root growth (Table 1), more P can be 

retained belowground to support new 

root development. Yet, this assumption 

is not supported by our observation 

in the greenhouse or previous 

studies where soil N fertilization 

generally increases the proportion of 

P allocated to aboveground tissues. 

Unfortunately, we did not sample roots 

for nutrient analysis in this study, and 

thus effects of soil N on root P concentration 

cannot be further examined. 

In addition to the two explanations 

presented above, we suspect that soil N 

applications might lower AMF colonization 

in roots and therefore decrease 

vine P uptake. 

The percentage of fine roots colonized 

by AMF (fungal hyphae, arbuscules, 

vesicles and spores) decreased with soil 

N supply in Year 2 and 3 (Table 1), in 

accordance with reduced vine P status 

in Chardonnay. The percentage of 

roots colonized by arbuscules also reduced 

in the soil N vines in Year 2, but 

not in Year 3. The greater suppression 

YEAR 1 

YEAR 2 




Crop Resilience 

Vineyards and orchards No N grow best 

in fungally dominant soil. 

Soil N 

Fungal networks of mycelia and 

mycorrhizae extend Foliar the N reach of 

roots to access nutrients and water. 

Beneficial fungi also No help N suppress 

disease and mitigate abiotic stresses 

like drought, salinity Soil and N heat. 

Biological fertility Foliar programs N renew 

YEAR 3 

the soil with diverse fungi, which 

increases humus and water-holding 

YEAR 3 

No N 

capacity. 

Soil N 

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3.2 

2.6 

2.7 

3.2 

2.9 

2.4 b 

4.0 a 

3.2 ab 

Produced on the Washington coast 

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88.5 a 

82.0 b 

87.3 a 

94.5 a 

90.9 b 

94.9 a 

92.2 

88.0 

94.7 

Vineyards, nut orchards, citrus groves, and cherry and apple orchards have 

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55.9 a 

47.0 b 

55.3 a 

48.8 

42.7 

45.8 

40.8 

40.4 

41.9 




Effect of Soil N Applications in Pinot Noir 

Similar to what we observed in Chardonnay, soil N applications 

improved vine N status in Pinot noir across three years 

(Fig. 3). Soil N fertilization also increased root growth and 

decreased mycorrhizal colonization in Pinot noir, although 

the effects were less evident as compared to Chardonnay 

(Table 2). The percentage of roots colonized by AMF was 

lower in the soil N vines than no N vines in two of three 

years, while the percentage of roots colonized by arbuscules 

reduced in the soil N vines only in one year. 

Even though soil N altered mycorrhizal colonization, it 

had no influence on leaf blade or petiole P concentration at 

bloom or veraison in any year, except petiole P concentration 

at bloom was lower in the soil N vines than no N vines in 

Year 2 (Fig. 3). Even so, P concentration of corresponding 

leaf blades was not affected by soil N supply, suggesting an 

overall small impact of N fertilization on vine P status in 

Pinot noir. The difference in how vine nutrition and mycorrhizal 

colonization responded to soil N application between 

Chardonnay and Pinot noir can be attributed to the difference 

in soil N and P availability. 

Figure 3: Effect of N applications to the soil and the foliage (soil 

N and foliar N) on petiole N and phosphorus (P) concentration at 

bloom in Pinot noir. Vines that received no N application (no N) 

served as the control. Means followed by different letters indicate 

significant difference between treatments in each experimental 

year based on a t-test or Tukey HSD test at 95% confidence. 


of arbuscular colonization in the soil N vines in Year 2 was 

likely attributed to the fact that more N (20 lbs N/acre) was 

applied in Year 2 than Year 3. Clearly, increased root growth 

played a role in the decrease of AMF in the soil N vines 

because root colonization usually lags behind root growth. 

Soil N fertilization might affect AMF through other mechanisms 

as well. For example, N fertilization could reduce the 

amount of carbon translocated from vines to AMF and, in 

turn, decrease P delivered by the fungus. Or soil N supply 

reduced N translocated from AMF to vines, resulting in a 

decrease of mycorrhizal colonization. 

Compared to the Pinot noir vineyard, the Chardonnay 

vineyard has lower soil N and higher P concentration. It 

seems soil N fertilization would suppress AMF colonization 

and decrease vine P status to a greater extent in vineyards 

with lower N and higher P availability. However, since the 

Chardonnay and Pinot noir vineyards differ in many other 

aspects, such as canopy size, irrigation and cropping level, 

the comparison between these two varieties are not straightforward. 

Thus, upon the completion of field experiments, we 

conducted a series of 

greenhouse experiments 

to further 

examine how N 

and P regulate vine 

nutrient status and 

mycorrhizal colonization 

under a more 

controlled environment. 

The negative 

effect of soil N applications 

on AMF was 

observed again in 

vines supplied with 

N at a high rate in 

the greenhouse. 

Effect of Foliar 

N in Chardonnay 

and Pinot Noir 

Foliar N applications 

had minor influence 

on vine N status, 

vine P status, root 

Chardonnay vines postharvest show a clear N 

effect on leaf color (photo courtesy T. Tian.) 


Foliar N 6.3 ab 94.3 a 33.7 


growth, and mycorrhizal colonization 

in both varieties (Figs. 2 and 3, Tables 

1 and 2). This is somewhat expected, 

since a large amount of N applied to 

the foliage appeared to be transferred 

to the fruit rather than other plant 

organs. 

Conclusions 

The evidence obtained from the field 

experiments indicates that soil N fertilization 

at moderate rates can negatively 

influence mycorrhizal colonization 

and reduces the benefits conveyed by 

this symbiotic relationship. Foliar N 

applications, on the other hand, had no 

impact on AMF or vine P status. The 

negative effect of soil N applications 

on mycorrhizal association provides 

another justification for being judicious 

with N fertilization in vineyards. 

YEAR 1 

YEAR 2 

YEAR 3 

YEAR 3 



No N 

Soil N 

Foliar N 

No N 

Soil N 

Foliar N 

No N 

Soil N 

Foliar N 


2.5 

3.2 

2.6 

2.7 

3.2 

2.9 

2.4 b 

4.0 a 

3.2 ab 

88.5 a 

82.0 b 

87.3 a 

94.5 a 

90.9 b 

94.9 a 

55.9 a 

47.0 b 

55.3 a 

Table 2: Effects of nitrogen fertilization to the soil and foliage (soil N and foliar N) on root density 

and colonized by arbuscular mycorrhizal fungi (AMF) in Pinot noir. Vines that received no N application 

(no N) served as the control. Means followed by different letters indicate significant difference 

between treatments in each experimental year based on a Tukey HSD test at 95% confidence. 

92.2 

88.0 

94.7 

48.8 

42.7 

45.8 

40.8 

40.4 

41.9 

This project was funded by Oregon Wine 

Board and USDA-ARS. The author 

would like to thank Erath winery and 

Results Partner Inc. for their help and 

support. 




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Grape Yield Prediction with Machine Learning 

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Simple Ways to Drive Soil Health 

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State of ACP and HLB in California 

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Powdery Mildew and Botrytis in Grapes 

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Cover Crops in California: What We Know 

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1:30 PM 

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Vine Mealybug in Grapevines 

Kent Daane, UCCE Specialist 

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