The Effect of Nitrogen and Clipping on Interference Between C 3 and C 4 Grasses

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Abstract
The effects of N deficiency and defoliation on the growth performance and compeititve interactions of Agropyron smithii (C3) and Bouteloua gracilis (C4) were studied in pot experiments. The results on the growth of N-deficient plants do not support the hypothesis that C4 plants have greater N efficiency than C3 species. Temperature is a major factor influencing the outcome of competition. A. smithii accumulates biomass faster than B. gracilis at 20.degree. C day/15.degree. C night conditions. The reverse is true at 30.degree. C day/15.degree. C night. B. gracilis exhibits a greater resistance to defoliation than A. smithii. The decrease in the crowding coefficient of A. smithii with respect to B. gracilis and the increase of the coefficient of B. gracilis with respect to A. smithii following clipping indicates that defoliation increases the competitive ability of B. gracilis. There is apparently a range of temperatures between 20.degree.-15.degree. C and 30.degree.-15.degree. C in which defoliation results in a shift in competitive outcome.

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