Nitrogen fixation and transfer of red clover genotypes under legume–grass forage based production systems

Nitrogen (N) is the most limiting available nutrient in most agro-ecosystems, where mineralization and assimilation of N are crucial processes in plant–soil systems. Inclusion of legumes as a source of biological nitrogen fixation in agricultural systems supports in supplying N for non-legumes while minimizing environment pollution associated with synthetic N fertilizer application. To better understand the efficiency of N fixation and transfer by red clover cultivars to companion bluegrass, a field study utilizing 15N dilution technique was conducted involving six diverse red clover cultivars over two growing seasons. The effects of red clover cultivars on N leaching and soil N cycling were also assessed during the growing periods by analyzing soil–water and soil samples for nitrate, ammonium, and total N under a bluegrass mixed stand. Significant differences were observed among red clover cultivars in the amount of N fixed during the first (0.26–1.43 g N plant−1) and second (0.29–1.56 g N plant−1) growing seasons but all cultivars derived more than 92 % of their shoot N from biological fixation. The proportion of interplant N-transfer from red clover to bluegrass progressively increased over time during this study with variation in this general trend between red clover cultivars. Significant differences among the red clover cultivars were observed for N-transfer to bluegrass and for N cycling patterns. These results indicate the potential for developing red clover cultivars specifically for mixed stands, improving N-transfer to companion grasses while minimizing N losses through leaching.