Biomass yield and nitrogen content of annual energy/forage crops preceded by cover crops

• All energy/forage crops had greater biomass yield, and total N content when preceded by a legume cover crop.
• Forage sorghum had the highest average biomass yield among the five energy/forage crops, with 17.8 Mg ha−1.
• Forage pea was the most suitable cover crop to provide additional N for the subsequent crops.
• Forage sorghum and sweet sorghum can be considered as the most productive energy/forage crops.

In order to reduce input costs and improve sustainability of energy/forage crops in the northern Great Plains (NGP), preceding cover crops can be included into existing annual crop systems. The objective of the study was to determine biomass yield and quality of five annual energy/forage crops, grown after six different, leguminous and non-leguminous cover crop species. The experiment was conducted at two locations, Fargo and Prosper, ND, from 2010 to 2012. The experimental design was a randomized complete block with three replicates, in a split-plot arrangement where the preceding season's cover crop was the main plot and the forage crop was the sub-plot. Six cover crops, forage pea (Pisum sativum L.) cv. Arvika, Austrian winter pea (Pisum sativum ssp. arvense (L.) Poir), hairy vetch (Vicia villosa Roth.) forage radish (Raphanus sativus var. niger) cv. Daikon, turnip (Brassica rapa var. rapa) cv. Purple Top, and forage turnip (Brassica campestris x napus) cv. Pasja, were planted no-till on 8 to 9 August in 2010 and 2011 into oat (Avena sativa L.) residue. In the following spring, five energy/forage crops, maize (Zea mays L.), forage sorghum and sweet sorghum (Sorghum bicolor L.), oat, and barley (Hordeum vulgare L.) were planted no-till onto the winter-killed cover crops residue. Results across locations and years indicated forage pea and forage radish, produced the highest dry matter yield (3.3 Mg ha−1) in the fall. Total plant N content was 116 kg N ha−1 in forage peas and 76 kg N ha−1 in forage radish, respectively. Results across locations and years indicated all energy/forage crops had greater biomass yield, and total N content when preceded by a legume cover crop compared with a non-legume or the check, in the previous year. Forage sorghum had the highest average biomass yield among the five energy/forage crops, with 17.8 Mg ha−1, followed by sweet sorghum with 15.3 Mg ha−1. In conclusion, forage pea was the most suitable cover crop to provide additional N for the subsequent crops in the NGP. Forage sorghum and sweet sorghum can be considered as the most productive energy/forage crops, especially when preceded by a legume cover crop.