Farm Table says:
Nitrogen is the most limiting nutrient and the most expensive fertilizer in cereal production. Enhanced crop yields are oft en associated with increasing N fertilizers, which may lead to low N use efficiency and environmental concerns due to N losses to waterways and to the atmosphere.
This study was undertaken to identify the most appropriate legume crop before corn and wheat production in the cool humid climate of Québec, eastern Canada. The objectives were to:
- compare the efficiency of grain legumes (soybean, pea, dry bean), legumes (crimson clover, alfalfa, hairy vetch) in monoculture or intercropped with a cereal (corn or wheat) to accumulate N under different soil and climatic conditions of Québec;
- evaluate the effects of the different legume crops on yield, N uptake, and agronomic N efficiency of subsequent corn and wheat;
- determine the optimal N fertilizer rate required to reach maximum corn and wheat yields and (iv) assess the effects of legume residues incorporation on soil N availability, soil aggregation and aggregate stability, and microbial activity.
Results and Discussion
Results of this study show that in growing conditions similar to those encountered at St-Mathieu-de-Beloeil, forage legumes need to be grown in monoculture than intercropped to produce high aboveground biomass and N returns, to increase subsequent crop yields and N nutrition, and to improve soil physical and biological soil properties.
The current study demonstrated that four legume systems (hairy vetch, crimson clover, alfalfa, and hairy vetch/ wheat) increased yields and N nutrition of corn and wheat at St-Mathieu-de-Beloeil site and of wheat only at St-Lambert-deLauzon. Also, soil macroaggregates, aggregate MWD, phosphatase alkaline, and dehydrogenase activity were increased following the above-cited legumes at St-Mathieu-de Beloeil site only.
Benefits of preceding legume crops on soil properties and on crop yields, N nutrition, and N use efficiency were more noticeable at a warmer site than at cooler location, probably due to better conditions for crop growth and residue mineralization. Legume grown under monoculture (hairy vetch, crimson clover, alfalfa) and hairy vetch/wheat also produced the greatest N fertilizer replacement value for subsequent corn (37–77 kg N ha–1) and wheat (5–37 kg N ha–1), although N credit for those legumes was <30 kg N ha–1. This implies that the non-N effects of these legume crops such as stimulation of enzyme activity and soil aggregation exerted an important positive effect on grain crop yield and N nutrition.
The results show that under warm climatic conditions, including forage legume crops in the rotation can provide a direct N contribution and indirect benefits to crops by improving soil fertility.