Nitrogen use efficiency and fertiliser fate in a long-term experiment with winter cover crops

The use of winter cover crops enhances environmental benefits and, if properly managed, may supplyeconomic and agronomic advantages. Nitrogen retained in the cover crop biomass left over the soilreduces soil N availability, which might enhance the N fertiliser use efficiency of the subsequent cashcrop and the risk of depressive yield and pre-emptive competition. The main goal of this study wasto determine the cover crop effect on crop yield, N use efficiency and fertiliser recovery in a 2-yearstudy included in a long-term (10 years) maize/cover crop production system. Barley (Hordeum vulgareL.) and vetch (Vicia sativa L.), as cover crops, were compared with a fallow treatment during the maizeintercropping period. All treatments were cropped following the same procedure, including 130 kg N ha−1with15N fertiliser. The N rate was reduced from the recommended N rate based on previous results, toenhance the cover crop effect. Crop yield and N uptake, soil N mineral and15N fertiliser recovered inplants and the soil were determined at different times. The cover crops behaved differently: the barleycovered the ground faster, while the vetch attained a larger coverage and N content before being killed.Maize yield and biomass were not affected by the treatments. Maize N uptake was larger after vetchthan after barley, while fallow treatment provided intermediate results. This result can be ascribed to Nmineralization of vetch residues, which results in an increased N use efficiency of maize. All treatmentsshowed low soil N availability after the maize harvest; however, barley also reduced the N in the upperlayers before maize planting, increasing the risk of pre-emptive competition. In addition to the year-longeffect of residue decomposition, there was a cumulative effect on the soil’s capacity to supply N after 7years of cover cropping, larger for the vetch than for the barley