Heavy rain chapters11/9/2022 ![]() The estimation of K s requires a daily water balance computation for the root zone. When the root zone depletion is smaller than RAW, K s = 1. Īfter the computation of K s, the adjusted evapotranspiration ET c adj is computed by means of Equation 80 or 81, depending on the coefficients used to describe crop evapotranspiration. P fraction of TAW that a crop can extract from the root zone without suffering water stress. TAW total available soil water in the root zone , K s is a dimensionless transpiration reduction factor dependent on available soil water , 84 where K s = 1 if D r, i RAW, K s is given by: Root zone depletion at the beginning of the day (column 8 of previous day),Įq. The expected ET o for the coming decade is 5 mm/day and K c = 1.2. Effect of water stress on crop evapotranspirationĮstimate the effect of water stress on the evapotranspiration of a full grown tomato crop (Z r = 0.8 m and p = 0.40) cultivated on a silty soil ( q FC = 0.32 and q WP = 0.12 m 3 m -3) for the coming 10 days when the initial root zone depletion is 55 mm and neither rain nor irrigations are either forecasted or planned. After the root zone depletion exceeds RAW (the water content drops below the threshold q t), the root zone depletion is high enough to limit evapotranspiration to less than potential values and the crop evapotranspiration begins to decrease in proportion to the amount of water remaining in the root zone (Figure 42).ĮXAMPLE 37. When soil water is extracted by evapotranspiration, the depletion increases and stress will be induced when D r becomes equal to RAW. At field capacity, the root zone depletion is zero (D r = 0). Water content in me root zone can also be expressed by root zone depletion, D r, i.e., water shortage relative to field capacity. ![]() This is accomplished by multiplying the crop coefficient by the water stress coefficient. The effects of soil water stress on crop ET are described by reducing the value for the crop coefficient. The effects of soil water stress are described by multiplying the basal crop coefficient by the water stress coefficient, K s:įor soil water limiting conditions, K s 8 mm d -1) to 0.70 for deep rooted plants at low rates of ET c ( RAW where plant moisture stress is an intentional part of soil water management. When the potential energy of the soil water drops below a threshold value, the crop is said to be water stressed. ![]() In dry soils, the water has a low potential energy and is strongly bound by capillary and absorptive forces to the soil matrix, and is less easily extracted by the crop. When the soil is wet, the water has a high potential energy, is relatively free to move and is easily taken up by the plant roots. Chapter 8 - ETc under soil water stress conditionsįorces acting on the soil water decrease its potential energy and make it less available for plant root extraction. ![]()
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