Nitrate Leaching From Grain Maize After Different Tillage Methods and Long/Short Term Cover Cropping.

The maize area in northern Europe has increased dramatically during the last 20 years, in Denmark from 19,000 ha in 1990 to 172,000 ha in 2010. Knowledge about nitrogen (N) leaching from maize under temperate coastal climate conditions is sparse. In 2009 an N leaching study was started in a field trial initiated in 1968 on a coarse sandy soil. The previous trial included spring sown crops undersown (with or without) perennial ryegrass (Lolium perenne L.) as cover crop, two N-rates (90 and 120 kg N ha^-1) and different tillage methods (shallow tillage and ploughing autumn or spring). With maize, each previous long-term treatment with soil tillage and cover crop was sub-divided into two, one with perennial ryegrass as cover crop and one without cover crop. The maize was sown in 2009 and 2010 and fertilized with 140 kg N ha^-1. The objectives were to determine the effects on leaching of i) previous history of long-term cover cropping, ii) soil tillage methods, iii) N rates and iv) present short-term use of cover cropping in maize. Preliminary results from 2009 – 2011 suggest that leaching after a history of cover cropping tended to be higher than after no history of cover cropping, but the effect was insignificant. The effect of tillage and previous N rates were also insignificant but the present use of cover crops had a small but significant decreasing effect on leaching compared to no cover cropping. The cover crop was well established in both years but grew less vigorously during autumn due to strong competition from the maize crop. The experiment shows that it is difficult for the perennial ryegrass variety used as cover crop to survive until harvest of grain maize and to reduce leaching substantially.