Biomass yield and nitrogen fixation of legumes monocropped and intercropped with rye and rotation effects on a subsequent maize crop

Abstract

The research is focused on an ecologically sound and highly productive cultivation system for fodder and/or biomass for thermal power generation on the basis of winter legumes and maize as subsequent summer crop, managed without additional nitrogen fertiliser. Therefore the yield of biomass and N-fixing capacity of a winter pea (Pisum sativum L.) and crimson clover (Trifolium incarnatum L.) monocropped and intercropped with rye (Secale cereale L.) were examined for five years in a field trial. In mid-June above-ground biomass of winter crops was removed and maize transplanted. The winter crops achieved maximum dry matter yield about three to five weeks before maturity. Mixed stands yielded more biomass than pure stands and exhibited greater yield stability. The relative advantage of intercropping, expressed as land equivalent ratio (LER), determined for intercropped winter pea/rye were 1.1 to 1.2 and for crimson clover/rye 1.3. At maturity, the amount of fixed nitrogen ranged between 178 kg N for crimson clover and 242 kg N ha^-1 for winter pea, respectively. At the end of anthesis (middle of June, harvesting stage for silage fodder) 75% and 88% of the total fixed nitrogen was achieved, for clover and pea, respectively. In intercropping the amount of fixed nitrogen was lower than in pure stands due to a lower seed density of the legume; however, the N-fixing efficiency was greater than in pure stands. N-release of the winter pea in a pure stand produced a maximum yield in maize (Zea mays L.) without additional N-fertiliser. An additional N mineral fertilisation of 75 to 150 kg N and 75 to 225 kg N was necessary to achieve maximum yields in maize following intercropped winter pea and crimson clover, respectively. Legumes in mixed stands with rye resulted in lower amounts of residual nitrogen after maize harvest. The beneficial effect of legumes on maize can be divided into N-effects and rotation effects. Both effects were positive regarding winter pea. The rotation effect of crimson clover in pure stands on maize was negative. Allelopathic effects and the high sensitivity of crimson clover to mineral nitrogen in the soil, released by residues of the preceding crop, winter rape (Brassica rapa L.), were discussed as the reason for this observation. The combination of the winter pea in pure stand and maize achieved the highest total biomass yield from winter and summer crops, unfertilised (156 dt ha^-1 dry). The combinations of intercropped legumes and maize produced biomass yields of 142 to 145 dt ha^-1. Because winter pea is highly susceptible to lodging, intercropping with low seed density of rye is recommended (3/4 winter pea, 1/4 rye). The rye crop prevents lodging by providing support and high rates of N-fixation are achieved with high seed density of pea. Intercropping with crimson clover and rye should be based on high seed densities of legumes, too because rye is highly competitive within those mixtures.