Nitrogen accretion and other soil changes in Tindall clay loam under Townsville stylo/grass pastures

Abstract

Soil changes after 3-15 years of fertilized leguminous pastures on Tindall clay loam soil at Katherine, N.T. were studied by comparison of leguminous pasture soils with their native counterparts. Soil organic carbon, total nitrogen, C/N ratio and pH were unchanged by the presence of Townsville stylo (Stylosanthes humilis). Available phosphorus (bicarbonate extraction) was significantly higher under legume pasture, reflecting its fertilizer history, but there was no pattern of increase with time, nor with quantity of fertilizer. Available nitrogen (boiling water extraction) was higher under legume pasture, and both the absolute value under legume pasture and the change in amount were correlated significantly with the age of the pasture. Available nitrogen after three years of legume pasture was equal to that under unimproved pasture, suggesting that gains in this period merely balanced losses during clearing and establishment.