Intercropping Forage Sorghum with Sunnhemp at Different Seeding Rates to Improve Forage Production

Abstract

Forage sorghum (Sorghum bicolor (L.) Moench) is well established in the Texas High Plains as a drought-tolerant forage that often requires additional feed to provide adequate protein for livestock. Intercropping sunnhemp (Crotalaria juncea L.), a legume, with forage sorghum, may increase crude protein. However, the optimal intercrop seeding ratio of sunnhemp to sorghum to improve crude protein content and maintain sufficient biomass is unknown. A two-year field experiment was conducted near Canyon, TX, USA, in 2020 and 2021 using sunnhemp intercropped at three seeding rates (16.8, 33.6, and 50.4 kg ha−1) with forage sorghum at four seeding rates (0, 2.8, 5.6, and 11.2 kg ha−1) under drip irrigation. This study was conducted to (1) evaluate growth potential for sunnhemp in a semiarid environment, (2) find a seeding ratio that can maintain forage sorghum dry matter production and improve forage quality, and (3) determine if a midseason harvest can be supported and further improve quality of the forage produced. Midseason, full-season, regrowth biomass, and forage quality were evaluated. Results indicated that a sunnhemp–forage-sorghum intercrop produced dry matter comparable to forage sorghum when sufficient heat units were obtained in the growing season. Forage with higher nutritive value was produced when the intercrop was harvested twice.