Comparison of Corn and Grain Sorghum for Dryland and Limited Irrigated Grain Production in the Southern High Plains.

Dryland and limited irrigated cropping systems in the Southern High Plains of New Mexico have been dominated by grain sorghum [Sorghum bicolor (L.) Moench] due to its drought tolerance and response to timely precipitation events. With the introduction of drought tolerant lines of corn (Zea mays, L.), better weed control, and higher prices for corn, interest has emerged for utilizing corn in place of sorghum in these scenarios. A 2-yr study was conducted in 2011 and 2012 at the NMSU Agric. Sci. Ctr. at Clovis to evaluate the effects of crop species, variety (traditional vs. drought tolerant), population, and irrigation timing on yield and plant composition. Crops used were corn (var. Pioneer AquaMax P1498 and Mycogen 23T75) and sorghum (var. Pioneer 86G32 and Alta Seeds AG2103). Planting rates (PR) were: low (32,110 and 61,750 seeds ha^-1) and high (39,520 and 86,450 seeds ha^-1) for corn and sorghum, respectively. Water treatments were: ‘dryland’ (DL), no irrigation; ‘critical water’ (CW), irrigation at tasseling/heading only; ‘critical stress’ (CS), no irrigation at tasseling/heading; and ‘irrigated’ (IR), water applied at 150% of monthly average precipitation. Irrigation water was applied via subsurface drip irrigation. Total rainfall plus irrigation amounts were: DL, 106 mm; CW, 209 mm; CS, 292 mm, and IR, 386 mm. When averaged over both yr, the drought tolerant P1498 corn var. produced more stable yields than 23T75 between the high and low plant populations across all water treatments. At the low PR, both corn varieties were similar. Yield was not affected consistently by PR in sorghum. The DL treatment had lowest yields for both crops and was more pronounced in corn. Sorghum had higher yields than corn in DL. Corn yield increase response was greater than sorghum with each successive addition of total water. Corn was more affected by water availability leading up to tasseling/heading stage of maturity than sorghum. Yield advantage was observed in corn over sorghum in this study when 292 mm or more of water was added during the growing season. Considering long-term average corn prices, crops that receive this amount of water may be able to produce enough yields to recoup corn seed costs over grain sorghum, even in drought years.