EFFECTS OF IRRIGATION AND FERTILIZER N ON N ACCUMULATION AND PARTITIONING IN WHITE BEAN AND SOYBEAN
White bean (Phaseolus vulgaris) is generally reported to be poorly nodulated, to fix less nitrogen than soybean and to show increased yields following N fertilizer application. The work reported here attempted to determine whether white bean was N-limited under field conditions by comparing it with soybean (Glycine max (L.) Merrill) for N accumulation in whole plants through the course of the growing season, and for N distribution among, and N concentration in, plant parts at maturity. The effects of N fertilizer and irrigation were tested in three field experiments. White bean and soybean crops were found to accumulate N at similar rates during the growing season. However, in soybean, the concentration of N in seeds was higher and the concentration in nonseed tissues lower than white bean. Differences between species for N concentrations were reflected in the allocation of N among plant parts. In both crops, fertilizer N always increased the concentration of N in seeds, and often did so in other plant tissues. Irrigation increased tissue N concentrations of plants grown on a loam soil, but decreased it on a sandy loam soil. White bean was more variable in N allocation and N concentration responses to N fertilizer and irrigation than soybean. These data indicate that, although it had much lower N2-fixation rates and comparable N demands, white bean was not more N-limited than soybean.Key words: Bean (white), soybean, irrigation, N fertilizer, N yield, N partitioning