Chicory increases the level of N fixation by companion legumes

For chicory (Cichorium intybus) to be successfully incorporated into short term pasture phases in mixed farming systems, it needs to be grown with a companion legume to meet its high nitrogen (N) requirements. It was hypothesised that chicory's superior ability to scavenge for N will deplete the system of mineral N more than a perennial grass, thus increasing the level of biological N fixation by companion legumes. A glasshouse study was conducted where chicory and perennial ryegrass (Lolium perenne) were grown as monocultures or in 50:50 mixtures with either lucerne (Medicago sativa) or subterranean clover (Trifolium subterraneum). Monocultures of lucerne or subterranean clover were also included. All pasture treatments containing chicory were shown to deplete the soil mineral N by approximately 110 mg N pot-1 more than the perennial ryegrass treatments. Pure subterranean clover treatments had significantly greater (P<0.05) estimated levels of biological N fixation (1818 mg N pot-1) compared with lucerne treatments (801 mg N pot-1). Combining subterranean clover with chicory in a 50:50 mixture resulted in 43.1 mg N fixed per g of legume dry matter (DM), which was significantly greater (P<0.05) than all other treatments including the pure subterranean clover treatment (29.3 mg N fixed per g of legume DM). Growing chicory and lucerne mixtures of 50:50 increased (P<0.05) estimated N fixed by 7.4 mg N fixed per g of legume DM compared to the pure lucerne treatments (24.2 mg N fixed per g of legume DM). It was concluded that when chicory is grown in 50:50 mixtures with subterranean clover or lucerne, the superior ability of chicory to deplete soil mineral N increases the level of N fixation by the companion legumes compared to when the legumes were grown in 50:50 mixtures with perennial ryegrass.