Soil NO3-leaching during growth of three grass–white-clover mixtures with mineral N applications

The effect of sward composition and grass species richness on soil NO3-leaching following the application of mineral N was tested on a very rapidly draining soil in a cool humid climate 2007 and 2008. The factorial split-plot experiment used NH4NO3 at three rates in three split applications to three different mixtures of white clover (Trifolium repens), timothy (Phleum pratense), blue grass (Poa pratensis), meadow fescue (Festuca pratensis), and reed canary (Phalaris arundinacea). Grass–clover composition of the sward induced two effects on NO3-leaching from the soil following the application of mineral N. Apparent fertilizer N replacement by white clover increased NO3-leaching while blue grass proportion reduced NO3-leaching. Summer application of mineral N amplified the phenological asynchrony between white clover and cool season species, like timothy, in the N cycle of mixed grassland. An increase of the number of grass species from two to four did not reveal any N-conserving effect that could be attributed to species richness.