Effect of soil fertility level on growth of cover crop mixtures and residual fertilizing value for spring barley

The use of cover crops may play an important role in ecological intensification of farming systems through their impacts on cycling and the availability of essential nutrients. However, little is known about the effect of soil fertility on the performance of cover crops and consequent nutrient dynamics. We performed a two-year field trial to quantify the effect of two soil fertility levels (low and moderate) on the growth and nutrient content of different leguminous and non-leguminous cover crop species and their mixtures, and on their fertilizing value for the succeeding crop.Overall, the growth and shoot nutrient content of cover crops in autumn was influenced by the species, mixture choices and soil fertility level. The growth of some species was less affected by fertility level than others. Among the legumes, fertility levels had no effect on the growth of lupin. Among the non-legumes, buckwheat had the highest biomass production as well as C:N ratio at a low fertility level, and in the first year was affected least by soil fertility level. However, buckwheat and lupin grown as a single species or in mixtures did not lead to yield improvements in the subsequent crop. Generally, legumes produced more biomass than non-legumes in the mixtures at the low fertility level, whereas non-legumes produced more biomass at the moderate fertility level. Growing a mixture of vetch and radish achieved the best synergetic effect and highest shoot N content. In both years, the greatest improvements in barley yields were achieved after vetch grown as a single species and in a mixture with radish (by up to 46 %). Rye was less competitive in mixtures than radish and buckwheat, and in the second year it had a negative effect on barley yield at the low soil fertility level, presumably due to pre-emptive competition for nitrogen. Soil fertility level had a greater effect on barley yields than cover crop treatments, as yield increments at the moderate fertility level amounted to 48 % in the first year and 64 % in the second year compared with the low fertility level.These results demonstrate that the cultivation of winter-persistent legumes alone or in a mixture with oilseed radish offers a promising tool for improving the yields of subsequent crops through nitrogen input and nutrient cycling on farms where soil fertility level is low.