Silage production potential of forage sorghum, pearl millet, and corn under limited irrigation



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Corn (Zea mays L.) silage is the principal feed ingredient of beef and dairy industries in the semi-arid Texas High Plains (THP), where potential evapotranspiration far exceeds the rainfall. Irrigated corn has long served the region’s industries by producing consistently high-quality silage, which is a major source of digestible energy and roughage. However, declining pumping capacity of irrigation wells hinders the supply of water for profitable corn silage production in the THP. Forage sorghum [Sorghum bicolor (L.) Moench] and pearl millet (Pennisetum glaucum L.) can be a viable alternative to corn silage due to their lower water requirement and relatively drought tolerant nature compared to corn. Sorghum and pearl millet have an edge on performance in semi-arid environments over corn, but silage quality of sorghum and pearl millet is somewhat poorer than corn. However, introduction of the brown midrib (BMR) trait has enhanced the nutrient composition of forage sorghum and pearl millet by reducing the lignin concentration compared to non-BMR type. Therefore, assessing the forage yield, forage quality, and water productivity of non-traditional BMR silage crops compared to traditional crops like corn could provide a new forage crop option to the THP growers. A field experiment was conducted at New Deal, TX during summers of 2018 and 2019 with the objectives: (1) to assess and compare the physiology, silage yield, and nutrient composition of BMR forage sorghum, BMR pearl millet, and corn under deficit irrigation in the THP, and (2) to assess soil water depletion patterns, water use efficiency (WUE), and silage yield of BMR forage sorghum, BMR pearl millet, and corn under deficit irrigation. The experiment was conducted in split-plot design with three deficit irrigation levels [I0 (55 mm), I1 (172 mm), and I2 (323 mm) in 2018 and I0 (29 mm), I1 (147 mm), and I2 (260 mm) in 2019] as main-plots, and five cultivars [P1498AM (corn), AF7401 and Silo700D (BMR sorghum), and Epic and Exceed (BMR pearl millet)] as sub-plots with four replications. The higher leaf water potential (LWP), stomatal conductance, leaf area index, and light interception resulted into higher biomass assimilation in I2 (36.1 and 36.6 Mg ha–1) compared to I1 (32.9 and 26.1 Mg ha–1) and I0 (26.1 and 18.1 Mg ha–1) irrigation treatments in 2018 and 2019, respectively. Sorghum and pearl millet cultivars showed higher water stress through lower LWP, stomatal conductance, and canopy-air temperature difference compared to corn. However, sorghum cultivars (33.8 and 31.4 Mg ha–1) yielded greater fresh biomass than pearl millet (32.1 and 24.9 Mg ha–1) and corn (26.7 and 27.7 Mg ha–1) in 2018 and 2019, respectively. Lower lignin content and higher digestible energy were observed in corn, followed by pearl millet and sorghum. From these results, it can be concluded that under water-stress conditions, BMR sorghum can produce higher silage yield with acceptable nutrient quality, but it cannot exceed the nutrient quality of corn for silage. The soil water depletion amount decreased with increasing irrigation water supply and was observed 105, 60, and 44 mm in 2018 and 57, 37, and 13 mm in 2019 in I0, I1, and I2 treatments, respectively. Similarly, fresh biomass yield and evapotranspiration (ET) were observed greatest in I2 irrigation treatment followed by I1 and I0; however, fresh biomass WUE was observed to be the highest in I0 (99.5 kg ha–1 mm–1) and I2 (100.2 kg ha–1 mm–1) irrigation treatments in 2018 and 2019, respectively. Among cultivars, water depletion depth was greater in sorghum and pearl millet plots (0–1 m) compared to corn plot (0–0.6 m) which resulted in greater total water depletion in sorghum (75 and 31 mm) and pearl millet (68 and 48 mm) plots than in corn plots (67 and 28 mm) in 2018 and 2019, respectively. The ET was not significantly different among the cultivars in 2018; however, significant differences were observed in 2019. Despite the differences in ET and water depletion amount among cultivars plots, average yield and WUE were the highest in sorghum cultivars followed by pearl millet and corn. These results confirmed the ability of sorghum and pearl millet to produce greater biomass per unit of water use compared to corn. This is partially attributed to their strong root system, which is clear from greater water depletion amount from deeper depths compared to corn plot. Overall, greater WUE and higher fresh biomass of forage can be achieved by sorghum cultivars compared to pearl millet and corn under limited irrigation conditions.



Forage crop, Silage, Sorghum, Pearl millet, Corn, Deficit irrigation, Water use efficiency