Effect of mixed cropping with lupin (Lupinus albus L.) on growth and nitrogen uptake in pasture grasses grown under manure application

The use of organic fertilizer is essential to ensure sustainable agricultural production. Because organic fertilizer normally acts as a slow-release fertilizer, improving its nutrient-use efficiency is important, particularly in terms of nitrogen (N) nutrition. In the present study, we attempted to increase the N-use efficiency of cattle farmyard manure (CM) in the cultivation of pasture grasses by mixed cropping with white lupin (Lupinus albus), which has been reported to decompose organic N in its rhizosphere. Timothy (Phleum pratense) and orchard grass (Dactylis glomerata) were cultivated with or without either lupin or soybean (Glycine max) in pots under three different N treatments (CM, ammonium sulfate, or no N). In the CM treatment, growth was higher in grasses cultivated with lupin than in those cultivated alone or with soybean. Moreover, decomposition of soluble organic N and protease activity in the rhizosphere soil of grasses with CM treatment were enhanced by mixed cropping with lupin. Analyses of microbial activity and bacterial community structure using Biolog EcoPlates suggested that the enhanced decomposition of soluble organic N was facilitated by lupin roots rather than by rhizosphere microorganisms.