Yield, seasonal changes in root competitive ability and competition for nutrients among grass species

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Abstract
SUMMARY: Root interactions between populations ofLolium perenne, Dactylis glomerata, Holcus lanatus and Anthoxanthum odoratumcollected from fertilized and unfertilized plots of the Park Grass Experiment were investigated at two levels of NPK over a period of 3 years.The root competitive abilities of species were dependent on fertilizer applications and changed with time. For example,L. perennewas more competitive at high nutrient application and during the early stages of the experiment. On the other hand, the root competitive ability of H. lanatus was greatest on unfertilized soil and increased with time. The large effect of root interaction on plant yield and the effects of fertilizer application on this, may be regarded as evidence of competition for one or more of the elements, N, P and K. H. lanatus, the most aggressive species, was more competitive on the unfertilized soil (NIL) than on the fertilized soil (NPK). However, this could not be confirmed by chemical analysis of plant material; there was no conclusive evidence that aggressive species contained higher concentrations of these nutrients when grown in mixtures with less aggressive species. The possibility of allelopathy, the production of toxins by one plant which inhibit the growth of another, cannot be precluded.The root competitive ability of species and populations was not positively correlated with the yield of species and populations in pure stand. Indeed, negative correlation was found especially on unfertilized soil. In this case varieties or species with a low yield in pure stand were highly successful root competitors in mixtures, while those with high yield in pure culture were poor root competitors.