Effect of mulching dates modified for nature conservation on the yield and nitrogen fixation of green manure lucerne crops

Abstract

Organically managed fields are highly attractive for wild animals of open agricultural landscapes because of a high percentage of green covered fields; for example, by green manures, catch crops and underseeds. Forage legumes are the main source of nitrogen in organic farming. Forage legumes are also important habitats for wild animals. The main ecological disadvantage is frequent mowing of forage crops. Increasing the time without disturbance in favour of wild animals may also decrease crop productivity and increase weed pressure. Here, we studied the effect of modified mulching dates on yield, nitrogen fixation and weed colonisation of lucerne green manure under pannonian site conditions during two vegetation periods in Eastern Austria. We compared a natural treatment, where the first mulching took place two weeks earlier and the second mulching two weeks later than in a conventional treatment with the latter. While in the first year the shoot dry-matter yield (−1.5 t ha−1), nitrogen yield and the amount of fixed nitrogen (−44 kg N ha−1) in lucerne were significantly lower in the natural than in the conventional treatment at the first cut, no differences could be detected in the second year. The seasonal amount of nitrogen fixation as well as the percentage of N derived from the atmosphere (Ndfa) at both cuts did not differ between the treatments. The natural treatment also had no disadvantageous effects on weed coverage. Our results show that prolonging the period without disturbance in lucerne crops had no adverse agronomic effects with only one exception: the 14-day shorter development period in the natural treatment at the first cut decreased shoot yield and nitrogen fixation compared with the conventional treatment in the first year, when weather conditions were humid before the first cut and dry afterwards. We therefore recommend shifting mulching dates and prolonging cutting intervals in lucerne on organic farms under pannonian site conditions in favour of wild animals.