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Modeling a Rye Cover Crop and Subsequent Soybean Yield

Dep. of Land Resource Science, Univ. of Guelph, Guelph, ON N1G 2W1, Canada

Leslie A. Hunt and Clarence J. Swanton

Dep. of Crop Science, Univ. of Guelph, Guelph, ON N1G 2W1, Canada

^* Corresponding author (criddle{at}lrs.uoguelph.ca).

Soybean [Glycine max (L.) Merr.] can be no-till seeded in the spring following a killed rye (Secale cereale L.) cover crop. A shortage of rain can affect soybean yields, depending on the timing of killing and the amount of mulch produced. Our main objective was to incorporate the effect of a rye mulch on soil water content into a soybean growth model (SOYGRO). The use of a wheat (Triticum aestivum L.) growth model (CERES-Wheat) for rye mulch production calculations and SOYGRO for predicting yields under no-mulch and mulch conditions were evaluated. The water balance subroutine of SOYGRO as modified to account for the effect of a rye mulch on soil water content due to mulch albedo, rain interception, and transmissivity of solar radiation. Data from previous experiments at Delhi (Psammentic Hapludalf soil), and Woodstock (Typic Hapludalf) in Ontario, Canada, were used to evaluate these modifications and yield predictions. Mulch production was described well by CERES-Wheat (r² = 0.96). The modified SOYGRO model improved soil water content calculations relative to the original model (r² = 0.67 vs. 0.58, root mean square error = 0.028 vs. 0.064 m³ m^–3). Simulated soybean yields were within 1 SD of measured values. In agreement with field measurements, the simulated effect of mulch did not increase soybean yields, and modification of SOYGRO to include mulch effects did not change yield predictions (r² = 0.83 vs. 0.81) when no prolonged drought occurred. The simple mulch model incorporated into SOYGRO was adequate to model the effect of rye mulch on soybean growth. The use of CERES-Wheat and the modified SOYGRO model in sequence under hypothetical drier weather conditions was demonstrated.

Received for publication November 3, 1995.