Abstract
Purpose Chicory ( Cichorium intybus ) scavenges more soil mineral nitrogen (N) than perennial ryegrass ( Lolium perenne ). A glasshouse study was conducted to test whether (a) the percentage of N derived from the atmosphere (%Ndfa) by a companion legume differs when grown with chicory or perennial ryegrass, and (b) there is an optimal ratio of non-legume:legume in a pasture mix that maximises biological N 2 fixation. Methods Chicory or perennial ryegrass was grown as a monoculture, or in a mixture with either lucerne (alfalfa, Medicago sativa ) or subterranean clover ( Trifolium subterraneum ) at 25:75, 50:50 or 75:25 ratio (non-legume:legume based on plant numbers). Monocultures of lucerne and subterranean clover were included as controls. Results All treatments containing chicory extracted more mineral N from the soil than corresponding treatments containing perennial ryegrass. Subterranean clover %Ndfa was greater than lucerne. Combining lucerne with chicory in a 50:50 or 75:25 mixture increased the efficiency of N 2 fixation by > 20%. Growing chicory with subterranean clover in mixtures of 50:50 or 75:25 resulted in the highest %Ndfa for growth among all treatments ( P < 0.05). However, the amounts of N 2 fixed by subterranean clover in the perennial ryegrass-subterranean clover mixture were similar to those in the chicory-subterranean clover mixture since dry matter accumulation from subterranean clover was higher when grown with perennial ryegrass. Conclusion The %Ndfa of legumes was greater when grown with chicory than perennial ryegrass. Chicory mixed with subterranean clover or lucerne in 50:50 ratios provided the optimum balance between legume dry matter yield and N 2 fixation.