Crop yield response to water - Cra
Crop yield response to water - Cra Crop yield response to water - Cra
opening and photosynthesis relative to maximum levels. The response of many fruit treespecies appears to be similar, although there is less solid evidence that for fruit trees and vinesthese two processes are as insensitive to mild water stress as they are for the major annualcrops. In addition to trees' stomatal regulation, in response to water status, crop load andother endogenous factors can also affect gas exchange rates, making it difficult to generalizethe observed patterns of stomatal behaviour across species. Also, there are gradients of waterstatus within the tree and these differences in water supply can induce partial stomatal closurefor some branches of the tree but not in others. The characteristic response of stomata towater deficits is shown in Box 16, where increasing stress levels impact both the magnitude ofthe peak and the plateau levels of stomatal conductance.Mechanisms involved in the responsesThe understanding of the physiological mechanisms involved in the response to water deficitsis well developed for water relations and hydraulic and chemical signals, but there is a needto have a framework that integrates these processes into a whole-crop model accounting forboth resource capture and efficiency in the use of resources. Box 17 shows the mechanismsbox 17 Physiological mechanisms of crop responses to soil water deficit.Pathway (1) involves direct root perception of soil water deficit, and root signals inducingreduction in shoot growth; the two-way arrow allows for shoot-to-root feedback signalling.Pathway (2) involves a strong, reinforcing loop of reduced shoot and root growth, which ismediated by impairment of the ability of root systems and canopies to capture resources.Pathway (3) involves reductions in the efficiency in the use of resources, as exemplified byradiation use efficiency (RUE) and transpiration efficiency (TE) (Sadras, 2009).(2)Reduced shoot growth(3)Reduced capture ofresources (radiation, CO 2)(2)(1)(2)Reduced RUE & TE(3)(2)(2)Reduced capture ofresources (water, N, P)Altered root function(2)Soil water deficitYield Response to Water of Fruit Trees and Vines 283
of crop responses to water deficits grouped into three classes. Pathway (1) involves rootto-shootand shoot-to-root hydraulic and chemical signals, which have attracted profuseattention. Pathway (2) contains a very strong reinforcing loop, whereby initial reduction ingrowth of shoot, root or both, forms a loop that may eventually override other processes.Pathway (3) involves changes in radiation- and transpiration-efficiency; these efficienciesare stable except for conditions of severe stress. This model illustrates the interactions andinterdependence of the multitude of physiological processes involved in water relationsand plant growth and, as such, is an integral part of understanding crop responses to waterdeficits. This understanding is fundamental and forms the basis for the development ofimproved irrigation practices.Effects on yieldKnowledge of yield and fruit quality responses to water deficits is required to predict theorchard response to reductions in water supply in water-short years or in areas of waterscarcity, where it is not possible to supply the amounts needed to meet maximum ET c .Normally, the prospect of water deficits increases the risk of yield reductions and these fearsare often realized if the water deficits are severe enough and occur at critical stages whensome of the components of yield are determined. However, it is sometimes possible to avoidthe negative impacts of reduced irrigation supplies by confining the plant water deficits tostress-tolerant periods of the season. Moreover, there are some cases where it is possible toactually exploit the positive responses to water deficits to improve fruit quality and thus,enhance crop value with reduced consumptive use. Thus, growers would profit from bothhigher gross revenue and reduced water costs.To assess the response of fruit trees and vines to water deficits, multiyear trials are necessarybecause perennial plants require time to acclimatize to a new water regime and becausethere may be carryover affects of water deficits on subsequent season(s)' productivity.In other words, stress history is an important aspect of permanent crop deficit irrigation.Normally, stored soil water, shoot, leaf, root, and fruit development are all affected by thefirst season of water deficits and all that influences the results of that year. After the firstyear, a minimum of two additional years are needed to evaluate the response, primarily is theresult of both carryover impacts of stress and the alternate bearing tendency of many treespecies that would affect the yield, regardless of the water deficits. To characterize the yieldresponse to water for perennial crops it is necessary to conduct experiments for 3-4 yearsminimum, and preferably more. The tree-to-tree variability increases the number of replicateplots needed to detect statistically significant differences in both physiological processes andyield components among treatments. All these make tree and vine irrigation experiments verytime consuming and expensive and thus scarce, particularly those that are long term.Fruit and product qualityMany fruit quality features may be affected by water deficits and it is ultimately the cumulativeimpact on yield and quality of a product that will inform deficit irrigation strategies. Thus,only those quality factors that influence product prices should be considered when evaluatingthe effects of water deficits on quality. The size of fresh fruit is one of the most importantquality aspects affecting orchard revenue. Fruit size is generally reduced by water deficits284crop yield response to water
- Page 248 and 249: with typical values around 10.5 g/m
- Page 250: ReferencesAlvarez-Jubete, L., Arend
- Page 254 and 255: Growth and developmentThe common me
- Page 256 and 257: soils (EARO, 2002). Tef has some to
- Page 258: tef 243
- Page 261 and 262: Lead AuthorsElias Fereres(Universit
- Page 264: equirements per unit land area for
- Page 268 and 269: figure 6 The water balance of an or
- Page 270 and 271: ox 2 Understanding the transpiratio
- Page 272: Orchard transpirationTree Tr is det
- Page 276 and 277: ox 4 Sample calculation of E dz , E
- Page 278 and 279: ox 5 Computing olive tree transpira
- Page 280 and 281: FIGURE 10 Crop coefficient (K c ) c
- Page 282 and 283: For training systems on a vertical
- Page 284 and 285: ox 7Consumptive and non-consumptive
- Page 286 and 287: are seeking more precision in their
- Page 288 and 289: ox 9 Examples of soil water monitor
- Page 290 and 291: ox 10 (CONTINUED)The major limitati
- Page 292 and 293: ox 12Definition of CWSI and an exam
- Page 294 and 295: The water budget methodWith this me
- Page 296 and 297: ox 15 Evolution of soil water under
- Page 300 and 301: that occur during the periods of fr
- Page 302 and 303: The crop, where price can vary more
- Page 304: Modify horticultural practicesPruni
- Page 307 and 308: FIGURE 13Comparison of yield per un
- Page 309 and 310: season. Thus the risks of salinity
- Page 312: 4.1 Fruit trees and vinesEditor:Eli
- Page 315 and 316: Figure 1 Production trends for oliv
- Page 317 and 318: Figure 2Occurrence and duration of
- Page 320 and 321: The use of displacement sensors to
- Page 322 and 323: Figure 4 Relationship between relat
- Page 324 and 325: Table 3 Sample calculation of month
- Page 326 and 327: clayey soils. If supply is very lim
- Page 329: Lead AuthorDavid A. Goldhamer(forme
- Page 332 and 333: Fruit growth during this stage is t
- Page 334 and 335: Season-long stressSeveral studies h
- Page 336 and 337: Table 1Published monthly crop coeff
- Page 339 and 340: Four crop-water-production function
- Page 341 and 342: size distribution toward more favou
- Page 344 and 345: Lead AuthorSAmos Naor(GRI, Universi
- Page 346 and 347: Apples tend to have a biennial bear
opening and pho<strong>to</strong>synthesis relative <strong>to</strong> maximum levels. The <strong>response</strong> of many fruit treespecies appears <strong>to</strong> be similar, although there is less solid evidence that for fruit trees and vinesthese two processes are as insensitive <strong>to</strong> mild <strong>water</strong> stress as they are for the major annualcrops. In addition <strong>to</strong> trees' s<strong>to</strong>matal regulation, in <strong>response</strong> <strong>to</strong> <strong>water</strong> status, crop load andother endogenous fac<strong>to</strong>rs can also affect gas exchange rates, making it difficult <strong>to</strong> generalizethe observed patterns of s<strong>to</strong>matal behaviour across species. Also, there are gradients of <strong>water</strong>status within the tree and these differences in <strong>water</strong> supply can induce partial s<strong>to</strong>matal closurefor some branches of the tree but not in others. The characteristic <strong>response</strong> of s<strong>to</strong>mata <strong>to</strong><strong>water</strong> deficits is shown in Box 16, where increasing stress levels impact both the magnitude ofthe peak and the plateau levels of s<strong>to</strong>matal conductance.Mechanisms involved in the <strong>response</strong>sThe understanding of the physiological mechanisms involved in the <strong>response</strong> <strong>to</strong> <strong>water</strong> deficitsis well developed for <strong>water</strong> relations and hydraulic and chemical signals, but there is a need<strong>to</strong> have a framework that integrates these processes in<strong>to</strong> a whole-crop model accounting forboth resource capture and efficiency in the use of resources. Box 17 shows the mechanismsbox 17 Physiological mechanisms of crop <strong>response</strong>s <strong>to</strong> soil <strong>water</strong> deficit.Pathway (1) involves direct root perception of soil <strong>water</strong> deficit, and root signals inducingreduction in shoot growth; the two-way arrow allows for shoot-<strong>to</strong>-root feedback signalling.Pathway (2) involves a strong, reinforcing loop of reduced shoot and root growth, which ismediated by impairment of the ability of root systems and canopies <strong>to</strong> capture resources.Pathway (3) involves reductions in the efficiency in the use of resources, as exemplified byradiation use efficiency (RUE) and transpiration efficiency (TE) (Sadras, 2009).(2)Reduced shoot growth(3)Reduced capture ofresources (radiation, CO 2)(2)(1)(2)Reduced RUE & TE(3)(2)(2)Reduced capture ofresources (<strong>water</strong>, N, P)Altered root function(2)Soil <strong>water</strong> deficitYield Response <strong>to</strong> Water of Fruit Trees and Vines 283
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