soil micronutrient deficiencies in the rice-wheat cropping system.pdf

Soil Micronutrient Deficiencies in
the Rice-Wheat Cropping System
Zn deficient Unaffected ZnSO 4
treated
M
icronutrient deficiencies in the Indo-Gangetic Plains (IGP) started emerging with
the adoption and spread of intensive agriculture in the region. Imbalanced use of
macronutrient fertilizers, decreased use of organic manure, reduced recycling of crop
residues, and bumper harvests in the past three decades have induced secondary and
micronutrient deficiencies in the IGP. In several areas with intensive cropping, zinc (Zn)
deficiency appeared initially and subsequently the deficiencies of iron (Fe), manganese (Mn),
boron (B), and molybdenum (Mo) were recorded. The severity of these deficiencies
depended on the soil conditions and the crop grown. Rice crop removes larger quantities
of micronutrients compared to wheat. Increase in fertility levels progressively increases the
total removal of micronutrients due to increased dry matter production.
Uptake (kg/ha) of Micronutrients by Rice and Wheat
Fertility Biomass (t/ha) Rice Wheat
level* Rice Wheat Zn Cu Mn Fe Zn Cu Mn Fe
Control 6.5 4.1 0.12 0.09 0.35 1.68 0.07 0.03 0.11 0.70
Low 8.8 7.5 0.17 0.13 0.57 2.51 0.12 0.05 0.21 1.30
Medium 12.9 10.2 0.25 0.19 0.80 3.43 0.17 0.08 0.28 1.83
High 14.5 12.4 0.30 0.22 0.97 4.06 0.20 0.09 0.33 2.33
* Control = 0:0:0;
Low = 60:30:30
Medium= 120:60:60
High = 180:90:90 of N:P 2
O 5
:K 2
O
Source: Gupta and Mehla, 1993

Rice and wheat are important in the national food security of the IGP. The rice-wheat
system, though remunerative, has resulted in the over-exploitation of the natural soil
resource base, which has been further enhanced by the imbalanced use of inputs. Continued
emphasis on maximization of food grain production without appropriate management
practies from a shrinking land resource base will result in further depletion of micronutrient
reserves. The simplest solution to alleviate micronutrient deficiency is the application of
micronutrient fertilizers to the crop.
Problems in Alleviating Micronutrient
Deficiencies
• Difficulty in the identification of field crop deficiency
symptoms.
• Variation in soil micronutrient status, soil pH, rainfall duration
and intensity, and seasonal fluctuations in the groundwater
levels and temperature regimes in the region.
• Inadequate facilities and field tests to validate critical levels of
soil and plant micronutrients in the region.
Source of Micronutrients
in Soils
• Soil parent material
• Industrial and urban
effluents
• Agricultural chemicals
and fertilizers
• Irrigation water
If micronutrient deficiencies that
constrain high productivity are not
identified, monitored, and alleviated,
the fertilizer use efficiency of costly
chemical fertilizers and other
agricultural inputs will be markedly
reduced. The projected micronutrient
demand for 2025 in India is expected
to increase by five to 10 times the
present consumption level (Sehgal,
1999). This would entail the use of
fertilizer nutrients in the right
proportion, with efficient application
methods and at the appropriate time
of crop growth. Also, it is essential to
augment the availability of native
nutrients by modifying soil
environment through
management practices in different
crops and cropping systems.
Projected Demand for Micronutrients in India
Total and Available Micronutrient Content of Indian Soils
Micronutrient Total content Available micronutrient
(mg/kg soil) (mg/kg soil)
Content
Mean
Zinc 2 to 1,019 0.2 to 6.9 0.9
Copper 1.9 to 960 0.1 to 8.2 2.1
Iron 2700 to 191,000 0.8 to 196 19.0
Manganese 37 to 11,500 0.2 to 118 21.0
Boron 3.8 to 630 0.08 to 2.6 -
Molybdenum 0.01 to 18.1 0.07 to 7.67 -
Source: Takkar, 1982; Singh, 1999

Extent of Micronutrient Deficiencies
The total micronutrient contents of soils are of limited value to plant growth and responses
to their application. To match the levels of micronutrients in soil with plant requirement,
their available contents in soils are determined. Like total contents, the available
micronutrient status of soils is also highly variable. Soil properties exercise a considerable
influence on the availability of micronutrients. Therefore, the extent of micronutrient
deficiency varies not only in different states and districts but also in different blocks within
the same district depending upon the soil characteristics and other management conditions.
Extent of Micronutrient Deficiency in the Soils of India
State No. of soil Percent soil samples deficient
samples Zn Cu Fe M n
Bihar 19214 54.0 3 6 2
Haryana 21848 60.5 2 20 4
Punjab 16483 48.1 1 14 2
Uttar Pradesh 26126 45.7 1 6 2
West Bengal 6547 36.0 0 0 3
Total 90218 50.6 2 10 3
Source: Singh, 1999
Areas of Deficiency
• Zinc deficiency is the most widespread in the four IGP countries (Bangladesh, India,
Nepal, Pakistan).
• Some areas in Punjab, India revealed a marked decrease in the extent of zinc
deficiency but there has been an increase in the deficiency of iron and manganese.
• The extent of iron deficiency is approximately a fifth that of zinc deficiency and is
largely influenced by the vast areas under alkaline to calcareous soil tracts.
• Iron deficiency is only second in importance after zinc deficiency in Punjab and
Haryana in India.
• Manganese deficiency is in localized sites where rice-wheat crop rotation is practiced in
coarse-textured soils.
• Copper deficiency is not widespread in the IGP, but deficiency based on plant analysis
is higher than soil analysis. The critical limits used for soil copper or plant copper need
to be re-calibrated.
• The incidence of boron deficiency was highest in the acid soils of West Bengal
followed by the calcareous soils of Bihar.
Diagnosis of Micronutrient Deficiency
The assessment of micronutrient deficiency can be made through visual leaf symptoms and
soil and plant analyses. Response of crops to the application of micronutrients not only
confirms the deficiencies but also helps in determining nutrient needs.

Deficiency Symptoms
Visual recognition of leaf symptoms is important in the
identification of nutrient disorders in crops. Nutrients like iron and
boron, which are not readily translocated from old to young leaves
under stress conditions within the plant are called immobile
nutrients and their deficiency symptoms first appear on young leaves. Due to the
Visual symptoms of zinc
deficiency in rice
plants first appear
on older leaves.
variable mobility of zinc, copper, molybdenum, and manganese under conditions of their
deficiency, the location of their symptoms in different crops and crop species may vary
depending upon the degree of their mobility. Confident diagnosis by this method, however,
requires much experience, as the symptoms of some nutrient deficiencies are difficult to
differentiate without a thorough knowledge. Another limitation of this technique is that by
the time the deficiency symptoms appear, the crop has undergone a marked set back and
the corrective measures taken at that time may not produce optimum yields. The diagnosis
by this method should be confirmed through soil and plant analyses followed by designing
experiments of crop response to the added micronutrient of interest.
Plant Analysis
Plant analysis is widely used as a means of detecting micronturient deficiency and the need
for fertilizing the crops. Under conditions of hidden micronutrient deficiency, plant analysis
is the most effective method for diagnosis of micronutrient disorders. This is because
neither the plant exhibits visual deficiency symptoms, nor do the soil tests precisely predict
such situations.
Soil Analysis
Soil analysis is an invaluable and convenient diagnostic tool for quick and timely assessment
of micronturient availability. Several chemical extraction procedures have been used to
measure the plant available micronutrients.

Critical Levels for Micronutrients in the IGP
Future Micronutrient Research Needs
The relatively minor problem of soil micronutrient deficiency at
the begining of the Green Revolution three decades ago is a
factor to reckon with in present times in sustaining the
productivity of rice and wheat in the IGP. The monoculture of
rice and wheat of the past has given rise to an exhausting soil
micronutrient feeder rice-wheat cropping system of the
present day. Proper management of the rice-wheat cropping
system is a key to minimize crop yield reduction induced by
micronutrient deficiency. There is a general lack of
awareness among farmers on micronutirent deficiency
problems. Except for the acknowledgment of zinc
deficiency (commonly known as khaira) by farmers,
existence of other micronutrient deficiencies is not a
common knowledge and under a “perceived” optimum
management condition, poor yields of rice and wheat
are often described by farmers as being due to “sickly” soils.
khaira
The critical micronutrient values for both soils and plants in the IGP have not been
extensively field tested; field validation will be of immense help to researchers and extension
specialists. Information on crop response to micronutrients and soil micronutrient analysis
in the IGP has been scattered. An ecoregional soil micronutrient status-analysis within the
IGP and synthesis of this information using geographic positioning system (GPS) and
geographic information system (GIS) will facilitate delineating regions of specific

deficiencies. This will help formulate on-farm diagnostic and adaptive research, spreading
of awareness amongst farmers, and extrapolating results to similar sub-ecoregions within
the IGP where intervention programs on micronutrients can be undertaken.
More information on the transformation and availability of micronutrients for different
soils and the effect of manipulating the soil physical environment and its moisture regimes
on plant available micronutrients need to be generated. Continuous use of farmyard
manure or of other organic sources arrests the depletion of available micronutrient pools
from soils. Development of integrated micronutrient technology using available organic
materials is needed not only to increase micronutrient use efficiency but also to decrease the
pressure on the use of costly inorganic micronutrient carriers. Field experiments have
proved the superiority of zinc sulfate as a zinc carrier. Increasing costs coupled with a
shortfall in supply of zinc sulfate has necessitated investigations on evaluating sparingly
soluble zinc sources or ores combined with zinc mobilizers. The residual availability of
various sources of micronutrients for a cropping system needs to be worked out.
For soils marginal in micronutrient supply, new interventions like seed treatment need
investigations to help save the costly micronutrient fertilizer. Micronutrients like boron
whose deficiency and toxicity limits for crops are very narrow require careful investigations
including its field testing for rates and frequency of application. Finally, the identification
and/or breeding for micronutrient efficient crop cultivars having either low micronutrient
requirement for potential yields or capable of mining micronutrients from the less available
pools should be given priority.
References
Gupta, V.K. and D.S. Mehla. 1993. Depletion of Micronutrients from Soil and their Uptake
in Rice-Wheat Rotation. Journal of Indian Society of Soil Science 4:704-706.
Sehgal, V. 1999. Indian Agriculture 1999. Indian Economic Data Research Centre, New
Delhi, India. 600 pp.
Singh, M.V. 1999. Micronutrient Deficiency Delineation and Soil Fertility Mapping. In:
National Symposium on Zinc Fertilizer Industry - Whither To (Ramendra Singh and
Abhay Kumar, eds.). Session II.
Takkar, P.N. 1982. Micronutrients: Forms, Contents Distribution in Profile, Indices of
Availability and Soil Test Methods. pages 361-391 In: Reviews of Soil Research in India.
Part 1. 12 th International Congress of Soil Science, New Delhi, India.
Adapted from:
Nayyar, V.K., C.L. Arora and P.K. Kataki. 2001. Management of Soil Micronutrient Deficiencies in the Rice-Wheat
Cropping System. pages 87-131. In: Kataki, P.K. (ed). The Rice-Wheat Cropping Systems of South Asia: Efficient
Production Management. Food Products Press, New York, USA.
Corresponding author:
V.K. Nayyar