EFFECTS OF IRRIGATION AND FERTILIZER N ON N2(C2H2) FIXATION AND YIELD OF WHITE BEAN AND SOYBEAN

Abstract

White bean (Phaseolus vulgaris L.) generally fixes less atmospheric nitrogen (N2) than does soybean (Glycine max [L.] Merrill). Experiments were conducted to assess the sensitivity of both species to irrigation and fertilizer N. Trials were conducted near Elora, Ontario in 1981 to 1983 and at Cambridge, Ontario in 1983. Treatments included applying 1 cm/day of irrigation water, 200 kg N/ha added throughout the season (400 kg N/ha at Elora in 1983), 1 cm/day of irrigation water plus N, and a control with no added fertilizer or water. Irrigation increased N2(C2H2) fixation in white bean by four to 150 times and in soybean by two to four times. Nodule mass and nodule size also were generally increased more in white bean than in soybean. Specific nodule activity (SNA) was increased similarly in both species. Fertilizer N decreased N2(C2H2) fixation consistently, and also lowered nodulation and SNA in most cases. The increase due to irrigation was the same in most instances under low or high N conditions. There was no indication that nodulation and N2(C2H2) fixation were more sensitive to fertilizer N in white bean than soybean. Fertilizer N application caused 10–20% increases in total N accumulation in each experiment, but seed yields were only increased by fertilizer N at the site with the least available soil N. N2(C2H2) fixation by white bean was much less than by soybean, yet seed yields of white bean were higher in two of the four trials. Yields in white bean appeared no more limited by available N than were yields in soybean.Key words: Phaseolus vulgaris, Glycine max, N2(C2H2) fixation, nodule development, seed yield