Biomass and forage nutritive value of spring-planted cover crops in a semiarid region

Abstract

Integrating cover crops (CCs) into cropping systems offers multiple benefits, including soil erosion control, nitrogen cycling, organic matter accumulation, weed suppression, and forage for livestock. Biomass, a key driver of these benefits, depends on species selection and adaptation to environmental conditions. In the western US's semiarid climate—characterized by cold, dry winters and short spring growing periods—CC options are limited due to winterkill risk and limited time between main crop cultivation. This study evaluated the biomass of 20 commercially available species, including grasses (seven), legumes (four), brassicas (three), and mixtures (six), grown from March to May at Sidney and Scottsbluff, Nebraska, in 2022 and 2023. At Sidney, Jerry oat (Avena sativa L.) had the greatest biomass (1.13 Mg ha⁻¹), exceeding other species by over 60%. At Scottsbluff, P919 barley (Hordeum vulgare L.) and a mixture of Lavina barley, 4010 pea (Pisum sativum L.), and Barsica rapeseed (Brassica napus L.) had the greatest biomass (0.71 Mg ha⁻¹). Grasses had 140% greater biomass than legumes and brassicas. Spring-planted CCs also had supplemental forage potential, with greater crude protein and total digestible nutrients, particularly in oat and barley. Growing degree days and precipitation explained 44% and 34% of biomass variation, respectively. All species had carbon-to-nitrogen ratios below 16. Despite lower biomass than reported thresholds, modest spring biomass of some species offers an alternative to winterkill or autumn planting constraints in semiarid systems. Results underscore the importance of selecting appropriate species suited to local conditions to maximize biomass and nutritive value.