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COMPUTERS IN AGRICULTURE

Effects of Estimating Soil Hydraulic Properties and Root Growth Factor on Soil Water Balance and Crop Production

^a USDA-ARS, Agricultural Systems Research, 2150 Centre Ave., Bldg. D, Fort Collins, CO 80526
^b Univ. of Georgia, 1109 Experiment St., Griffin, GA 30223

^* Corresponding author (Liwang.Ma{at}ars.usda.gov).

Accurate simulation of plant growth depends not only on plant parameters, but also on soil parameters. Although there is uncertainty in measured soil parameters and root distributions, their effects on simulated plant growth have been much less studied. This study evaluates the simulated responses of six crops, wheat (Triticum aestivum L.), maize (Zea mays L.), barley (Hordeum vulgare L.), soybean (Glycine max L. Merr.), peanut (Arachis hypogaea L.), and chickpea (Cicer arietinum L.), under various water and N management to different methods of estimating soil hydraulic properties and soil root growth factor (SRGF) in root zone water quality model (RZWQM2) that contains the decision support system for agrotechnology transfer (DSSAT) Version 4.0 plant growth models. The two methods of obtaining the soil water retention curve (SWRC) in RZWQM2 were based on (i) known soil water contents at both 33 and 1500 kPa suctions, or (ii) soil water content at 33 kPa only. The two methods of estimating saturated hydraulic conductivity (K_sat) were (i) soil texture class based average K_sat or (ii) K_sat calculated from effective porosity (difference between soil water contents at saturation and at 33 kPa). For the six crops, simulation results showed that the soil water balance was affected more by K_sat than by SWRC, whereas the simulated crop growth was affected by both K_sat and SWRC. Small variations in the SRGF did not affect soil and crop simulations, and SRGF could be estimated with a simple exponential equation.

Abbreviations: AET, actual evapotranspiration • CSM, crop system model • DSSAT, decision support system for agrotechnology transfer • DUL, drained upper limit • ET, evapotranspiration • K_sat, saturated soil hydraulic conductivity • LL, lower limit of plant extractable water • PET, potential evapotranspiration • PTF, pedotransfer function • RZWQM2, root zone water quality model • SRGF, soil root growth factor • SWRC, soil water retention curve

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Received for publication November 24, 2008.