Yoneyama, T and Engelaar, W M H G and Kim, H Y and Rupela, O P (2001) δ15N values of sorghum grains harvested on a Vertisol in the semi-arid tropics were positively related to doses of fertilizer N but negatively with the frequency of legume cultivation. Soil Science and Plant Nutrition, 47 (2). pp. 423-427. ISSN 0038-0768