Planting Geometry Influences Forage Yield, Nutritive Value, and Water Use Efficiency in Summer Cereal-Cowpea Intercropping Systems

Despite declining water availability in semi-arid environments, demand for high-quality forages by the livestock and dairy industries continues to grow. Researching alternative crops for high quality forage and water use efficiency remains a priority for these regions to meet this growing demand. Cereal grass-legume intercropping system may provide such a viable alternative to traditional sole cropping to improve nutritive value, while maintaining the current yield levels with limited supply of water. A study was conducted near West Texas A&M University, Canyon, TX, USA. during 2020 and 2021 to evaluate forage sorghum [Sorghum bicolor (L.) Moench]-cowpea [Vigna unguiculata (L.) Walp] and pearl millet [Pennisetum glaucum (L.) Leeke]-cowpea intercrops for forage production, nutritive value (crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), and in vitro dry matter digestibility (IVTDMD)), and water use efficiency (WUE) under limited irrigation. Treatments were sole pearl millet (PM), sole forage sorghum (FS), sole cowpea (C), or mixtures of either pearl millet-cowpea or forage sorghum-cowpea planted in the same row (PM-C or FS-C), alternating rows (millet-cowpea 1:1 (PM-C 1:1) or forage sorghum-cowpea 1:1 (FS-C 1:1), or two rows alternating (millet-cowpea 2:2 (PM-C 2:2) or sorghum-cowpea 2:2 (FS-C 2:2). Results from both study years indicated that FS-C 1:1 intercrop showed either greater or equal forage dry matter (DM) yield compared to sole FS or sole PM (14.5 Mg ha−1 (FS-C 1:1) vs. 13.8 Mg ha−1 (FS) vs. 11.9 Mg ha−1 (PM)). Similarly, the relative advantage of FS-C 1:1 intercrop in improving WUE was also observed in the study compared to sole FS and sole PM (44 kg ha−1 mm−1 (FS-C 1:1) vs. 41.6 kg ha−1 mm−1 (FS) vs. 35.9 kg ha−1 mm−1 (PM). CP yield per hectare (estimate based on DM yield and percent CP content) was also greater for the forage sorghum-cowpea planted in 1:1 alternate rows. This suggests that producers in the semi-arid USA, especially in the Southern High Plains, can be significantly benefited from the utilization of cereal grass-legume intercropping production systems in lieu of sole cropping as the basis for livestock rations without compromising yield and water productivity.