Effect of deficit irrigation on physiology and forage yield of forage sorghum, pearl millet, and corn

The declining Ogallala aquifer in the Texas High Plains may no longer meet the irrigation requirement to produce high water-demanding forage crops like silage corn (Zea mays L.) to support a large number of beef and dairy enterprises. Forage sorghum (Sorghum bicolor L.) and pearl millet (Pennisetum glaucum L.) can be viable alternatives to silage corn due to their relative drought tolerance than silage corn. A field experiment was conducted at New Deal, TX to assess and compare the physiology, forage yield, and nutrient composition of the brown midrib (BMR) forage sorghum, BMR pearl millet, and corn under deficit irrigation in 2018 and 2019. The experiment was conducted in a split-plot design with three irrigation levels (I-0 [50 mm], I-1 [200 mm], and I-2 [350 mm]) as main-plot and five cultivars (P1498AM [corn], AF7401 and Silo700D [BMR sorghum], and Epic and Exceed [BMR pearl millet]) as sub-plot with four replications. The higher leaf water potential (LWP), stomatal conductance, and leaf area index resulted in greater biomass assimilation in I-2 compared to I-1 and I-0 irrigation treatments in both years. Sorghum and pearl millet cultivars showed lower water status through lower LWP and canopy-air temperature difference compared to corn cultivar. However, sorghum cultivars yielded greater fresh biomass than pearl millet and corn in both years. Lower lignin concentration and higher digestible energy were observed in corn, followed by pearl millet and sorghum. These results suggest that under water-stress conditions BMR sorghum can produce higher forage yield with acceptable nutritive value.