The response to phosphorus of white clover and lotus inoculated with rhizobia or given KNO3

Abstract

Abstract White clover and lotus were grown in a controlled environment at P levels of 50, 500, and 1500 ppm and either inoculated with rhizobia (N2) or given KNO3(NO3). N2 plants of lotus and white clover had different responses to P. The response of NO3 plants to P was the same in both species. This implies that the reason(s) for the difference in response between N2 plants lie in differences in the structure and function of the symbiotic association. Lotus plants had a greater proportion of plant dry weight, P, and N in their nodules than did white clover. White clover nodules had higher relative growth rates and relative rates of accumulation of P and N than those of lotus and, in the early stages of growth, were more efficient. At 1500 ppm P, the yield of NO3 plants was greater than that of N2 plants in both species. It is suggested that the growth of N2 plants at the high P level was limited by N. These plants appear to have been unable to fix sufficient N for them to have yields similar to NO3 plants.