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Excess Soil Water Stress |
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Excess Soil Water Stress |
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Excess Soil Water Stress
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Excess Soil Water Stress |
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Excess Soil Water Stress |
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The method for quantifying the effect of high water tables on crop yields uses the stress day index concept (SDI) developed by Hiler (1969). The model for predicting corn yield response to excessive soil water conditions was developed by Hardjoamidjojo et al. (1982). The equation relating relative yields to wet stresses may be summarized as,
YRw = YRDMAX DSLOPE * SDIw
where YDRMAX is the intercept and DSLOPE is the slope of the linear relationship relating stress to relative yields. It should be noted that YRw is between 0 and 100%. YRDMAX may be larger than 100 for cases when the crop can tolerate some excess water conditions without yield loss. SDIw is the stress day index for excess water conditions and can be expressed as,
N
SDIw = SUM (CSwj * SDWj )
j=1
where N is the number of days in the growing season, CSwj is the crop susceptibility factor for excess soil water on day j and SDWj is the stress day factor for day j. In DRAINMOD, the SEW value is used for the stress day factor, SDWj. Crop susceptibility factors for corn and soybeans were obtained from studies by Evans et al. (1990a) and are given in Table 14. These factors are dependent on the stage of plant development. They were normalized so that the sum of the factors for the five growth stages is 1.0. These values are based on data collected since the original study by Hardjoamidjojo et al. (1982). Reevaluation of the Hardjoamidjojo et al. (1982) results plus new data on corn and soybean response to flooding resulted in the following equation parameters for yield response to excessive soil water stresses Evans et al., 1990b); YRDMAX = 102 and DSLOPE = 0.75 for corn and YRDMAX = 103 and DSLOPE = 0.70 for soybean.
Table 14. Crop susceptibility factors (corn and soybean) for excessive soil water conditions.
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CORN Days after planting
Growth Stage ___________________________________________ Crop susceptibility
130 Day Maturity 110 Day Maturity factor, CSw
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DAP
Establishment 0 - 29 0 - 19 0.20
Early Vegetative 30 - 49 20 - 35 0.22
Late Vegetative 50 - 69 36 - 50 0.32
Flowering 70 - 89 51 - 69 0.19
Yield Formation 90 - 109 70 - 89 0.08
Ripening > 110* > 90* 0.02
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* Use growing season length as end of growth stage.
Soybean Development Days after* Crop Susceptibility
Growth Stage Stage planting factor, CSw
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Establishment V2 0 - 24 0.19
Vegetative V5-V6 25 - 54 0.13
Flowering V9-R1 55 - 74 0.19
Pod Development R3 75 - 94 0.26
Pod Filling R5 95 - 109 0.25
Ripening (Pods w/full size beans) R6 110 - 119 0.08
(Pods yellowing) R7 120 - 129 0.01
(Pods brown) R8 130 - 140 0.00
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* Values are for soybean in maturity group V. Initiation of flowering is day
length sensitive and depends on maturity group. Adjust days after planting
accordingly.