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Simulating Forage Sorghum Yields with SORKAM

Agronomy Dep., Kansas State Univ., Manhattan, KS 66506

Ronnie W. Heiniger and Ahmed Z. Abelhalim

Vernon James Res. & Ext. Ctr., Plymouth, NC 27962
Agric. Res. Ctr., Giza, Egypt

^* Corresponding author (agrojof{at}ksu.ksu.edu).

A validated crop model can be a valuable tool for evaluating new production and management practices, particularly for crops routinely grown in environments that produce large variation in field performance tests. Previous work has been done to validate SORKAM a crop growth model for grain sorghum [Sorghum bicolor (L.) Moench]. The purpose of this study was to determine the ability of SORKAM to simulate forage sorghum yields for a wide range of environmental conditions. Data for the simulations used in the validation process were taken from performance tests for four cultivars (‘Early Sumac’, ‘Atlas’, ‘Sugar Drip’, and ‘Canex’) conducted at two sites in Kansas over 25 yr. Simulated bloom date, grain, stover, and total dry matter yields were regressed on measured data. The SORKAM model simulated bloom dates without bias; however, the root mean square error (RMSE) was 8 d, and the model tended to overestimate bloom date under conditions of water deficit. The model generally overpredicted yields of the four cultivars for grain (bias = 3.2 Mg ha^–1), stover (bias = 2.0 Mg ha^–1), and total dry matter (bias = 5.2 Mg ha^–1). In addition to overestimation of total dry matter production, weaknesses in the SORKAM model in simulating forage sorghum growth included inability to simulate phenological development accurately under moisture deficit stress and to partition dry matter into grain and stover. These problems must be resolved before SORKAM can be used to address management decisions.

Received for publication June 23, 1995.