Submitted to: Biological Systems Simulation Group Proceedings
Publication Type: Proceedings
Publication Acceptance Date: February 15, 2004
Publication Date: March 8, 2004
Citation: Baumhardt, R.L., Howell, T.A. 2004. Deficit irrigation, seeding practices, and cultivar maturity effects on simulated grain sorghum yield. In: Biological Systems Simulation Conference, March 8-10, 2004, Gainesville, Florida. p. 13. Technical Abstract: Irrigated sorghum producers on the southern High Plains face difficult management decisions governing crop yields and production costs, which are further complicated by declining irrigation capacity due to increased pumping costs or decreased water availability. Cultural practices are often chosen based on individual experience; however, as irrigation technologies evolve and cultivar choices expand, the resulting management options include untested combinations. Our objectives were to identify cultural practices that optimized long-term sorghum production. We used the computer simulation model, SORKAM, to calculate sorghum growth and grain yield for all combinations of cultivar maturity (early-15 leaf, medium-17 leaf, and late-19 leaf), planting date (15 May, 5 June, 25 June), population (12 and 16 plants m**2), row width (0.38 or 0.76 m), and irrigation capacity (maximum water replacement of 2.5 and 5.0 mm d**1). SORKAM was validated by comparing a subset of measured yields with the corresponding simulated yields where known cropping and soil water conditions were used as input. Subsequently, grain sorghum yields were simulated for the same soil conditions using long-term (1958-1999) weather records from Bushland, TX. Those yields show a complex relationship between irrigation levels, planting date, and cultivar maturity. That is, early maturing varieties yielded more than medium and late maturing varieties if irrigated at the 2.5 mm d**1 limit; however, the late-maturing variety planted on 15 May and receiving 'full' (5.0 mm d**1) irrigation yielded more than the other planting date and cultivar combinations. Late planted sorghum usually did not mature or reach full yield potential compared with the typical 5 June planting date. Sorghum planted in narrow 0.38-m rows increased grain yield 8% more than conventional 0.76-m rows. Overall mean yield was unaffected by plant population since plant tillering offset differences in the number of heads. As irrigation capacity decreases, sorghum yield can be optimized by shifting from planting late maturing cultivars on 15 May to planting early maturing cultivars on 5 June.