The effect of nitrogen and phosphorus supply on the competition between Cenchrus biflorus and Alysicarpus ovalifolius  [1982]

Gillard, P. Elberse, W.T. (Centrum voor Agrobiologisch Onderzoek, Wageningen (Netherlands))

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The effect of N and P supply on competition between the grass Cenchrus biflorus and the legume Alysicarpus ovalifolius was measured in a replacement experiment on sand culture in a climate room. Two levels of N and P were applied in all possible combinations, resulting in four treatments: P(,0)N(,0), P(,1)N(,0), P(,0)N(,1) and P(,1)N(,1). In monoculture the grass responded to both P(,1)N(,1) and P(,0)N(,1), but not to P(,1)N(,0). The legume responded in monoculture only to P(,1)N(,0). In all treatments relative yield total exceeded unity. Only in the P(,1)N(,0) treatment some mixtures yielded more than the highest-yielding monoculture, namely those mixtures where Alysicarpus dominated. Cenchrus was the stronger competitor in all treatments. When N was limiting, the weights per plant of the grass in mixtures were greater than those in monoculture, whereas the weights per plant of the legume were close or equal to those in monoculture (in the P(,0)N(,10) and P(,1)N(,0) treatment respectively). This indicates that the grass experienced hardly any competition for N from the legume, which was self-sufficient in its N supply. However the severe N limitation prevented the grass from depressing the legume in th competition for other resources. The positive response of the legume to P (in P(,1)N(,0)) was just enough to consolidate its position and to enable stable coexistence. Where N was applied the grass had a strong advantage in competition for P (in P(,0)N(,1))
or in light competition (in P(,1)N(,1)). It was concluded that the rapid growth of C. biflorus enabled it to capture resources early, making it the stronger competitor. Although A. ovalifolius grew more slowly it was adapted to survive in conditions of low nitrogen availability.

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Netherlands Journal of Agricultural Science (Netherlands)