Interpreting Indicators of a Transfer of N from Legume to Grass in Competition Studies

Interpreting Indicators of a Transfer of N from Legume to Grass in Competition Studies

The transfer of N from legume to grass in mixtures is important for regulating competition. In competition studies which include both monocultures and mixtures, N transfer should be detectable by grass N measurements but may be masked by competitive reductions in grass growth. In the study reported here, whole plant DM and N were measured in Panicum maximum var trichoglume and Neonotonia wightii grown in monocultures and additively in mixtures. While competition reduced whole grass plant DM and N in mixture relative to monoculture, higher grass shoot % N and N yield in the mixture at early harvests appeared reliable indicators of N transfer. In another experiment, monocultures and mixtures were grown in a replacement series with and without rhizobial N fixation. Higher grass shoot %N was a reflection of lower grass plant density in the mixtures. However grass shoot N yields in the mixtures consistently greater than in monoculture over at least a few harvests appeared a reliable indication of N transfer.