Crop yield response to water - Cra

Table 1b Summary of recommended olive K c values.Climate* Semi-arid AridSpring 0.65-0.75 0.45-0.55Summer 0.50-0.55 0.50-0.55Fall 0.60-0.70 0.55-0.65Winter 0.65-0.75 0.40-0.55* Mediterranean-type climates; the one labelled semi-arid has seasonal rainfall values around 500 mm or more, mostly betweenautumn and spring, while the arid climate would have less than 400 mm rainfall and is more continental, with relatively coldwinters. The higher K c values of the range should be used for high rainfall situations. K c values to be used with ET o calculatedfollowing FAO I&D Paper No. 56.from 0.55 to 0.65, depending on the season. A synthesis of current estimates of K c developedrecently (Fereres et al., 2011) is given at the end of Table 1b.Despite the evergreen nature of the olive, the K c is not constant throughout the year, becauseof tree transpiration responses to environmental and endogenous factors. Measurements haveshown that relative transpiration is lowest in spring and highest in early autumn. However, theK c also must reflect the rate of evaporation from the soil surface, which is quite high in springin many Mediterranean environments. Thus, K c values reflecting olive orchard water use do notdiffer as much between spring and autumn (see Table 1). In midsummer relatively low valuesof K c are found because of partial stomatal closure in response to high vapour pressure deficit.If more precise estimates of water use are needed, an alternative method has been proposedto calculate transpiration and evaporation independently (Orgaz et al., 2006) (See Chapter 4,Box 5). For table or canning fruit production, the higher range of K c values is recommended.Crop coefficients should be further increased (up to about 0.8 to 1.0 in winter and early spring,depending on the type of the cover crop and its density) if the orchard floor has a permanentgrass cover.Water Production FunctionOlive fruit yield decreases as ET c decreases below its maximum. However, it has been foundthat the decline in production is hardly detectable with small reductions in ET c (Figure 4). AsET c is further reduced, however, yields decline more. Thus, the response curve of yield (fruitor oil) to ET c is almost linear at low levels of consumptive water use, but levels off whenwater consumption is high. As a result, the overall response curves are parabolic and can bedescribed by second order equations, such as the one presented in Figure 4. The shape ofthe curve implies that the water productivity (WP) increases as ET decreases and, therefore,one can find an economic optimum, in terms of ET and therefore of irrigation amount, if theprice of oil and the irrigation water costs are taken into consideration. The curve shown inFigure 4 is the best fit line to a dataset obtained for the cv. Picual at Cordoba, Spain (Morianaet al., 2003). Additional data published for the cvs. Arbequina, Morisca, Mulhasan, Frantoio,Leccino, and also for the cv. Picual collected at another location, are also plotted in Figure 4.It appears that the data from other varieties/locations fall within the margins of error, on thecurve originally obtained at Cordoba, with perhaps the cv. Morisca showing higher sensitivityOlive 307