Spring barley grown for decades with straw incorporation and cover crops: Effects on crop yields and N uptake

Abstract Straw incorporation and cover cropping are important measures for reducing loss of nitrate by leaching and supporting soil quality in cereal cropping systems. However, cereal straw also represents an important source of bioenergy, while concerns still exist regarding a negative effect of annual straw incorporation on crop yields. Based on a field experiment initiated in 1981 on a sandy loam soil at Askov Experimental Station (Denmark), we examined the effect of annual addition of straw (0, 4, 8 and 12 Mg ha−1), undersown cover crops (ryegrass and ryegrass-clover), and ploughing time (autumn and spring) on spring barley yields and N uptake in grain and grain-free aboveground biomass. During 1981–2019, grain yields showed an annual increase of 0.05 Mg DM ha−1 while grain N concentration decreased 0.019 %-point yr−1. Straw incorporation rate had a significant effect on grain yield in only six out of 31 years. The effect of increasing straw rates was slightly negative in two of the initial years but positive in the extreme drought year 2018. During 2004–2018, an undersown grass-clover cover crop increased grain yield with 0.41 Mg DM ha−1 and grain N concentration with 0.13 %-point, corresponding to relative increases of 9% when compared to no cover crop. In contrast, an undersown ryegrass cover crop reduced grain yield with 0.21 Mg DM ha−1 corresponding to a relative reduction of 5%, and increased grain N concentration with 0.03 %-point corresponding to a relative increase of 2%, as compared to no cover crop. The time of incorporating straw and cover crop residues had a minor effect on barley yield and quality. Our results suggest that removal of straw for bioenergy does not compromise yields of spring barley grown at this site, while an inclusion of undersown leguminous cover crops had a pronounced positive impact on crop yield and quality. However, implementation of these management measures needs to be site-specific and consider trade-offs between effects on crop yield and quality, environmental benefits, and soil quality.