Estimation of nitrogen fixation by four legumes in a dry monsoonal area of north-western Australia

Abstract

The amount of nitrogen fixed by the legumes Townsville lucerne (Stylosanthes humilis), guar (Cyamopsis tetragonoloba), cowpea (cv. Poona), and peanuts (cv. Natal common) on Tippera clay loam was determined in the field for three seasons of growth. The total amount added to the soil-plant system in the three seasons by the four legumes was respectively 196, 196, 240, and 111 lb nitrogen an acre. The results indicate that Townsville lucerne fixed annually 83 lb nitrogen an acre in the second and third season. Cowpea and peanuts fixed less in the second and third season because of an increase in available soil nitrogen. Only with guar and Townsville lucerne was the original nitrogen status of the soil maintained.