Abstract: The responses of Cassia senna (L.) to added nitrogen, phosphorus and potassium in the semi-arid zone of central Sudan was investigated. The study was carried out by soil mechanical and chemical analysis and soil-culture experiments. The results of soil analysis showed that the sandy loam soil of the investigated site was a slightly alkaline (pH = 7.74±0.65) (characterized with high levels of Ca, adequate quantities of Mg, K and Na and low levels of NH4-N and P. Mn levels, however, were very low and associated with soil alkalinity. The growth response of C. senna (L.) to a range of separate additions of phosphorus treatments was higher compared with that of corresponding nitrogen treatments and this most likely because C. senna (L.) is a leguminous plant capable of fixing nitrogen in the root nodules. The analysis of variance of the results of the factorial additions of N, P and K to C. senna (L.) growing in a soil collected from the investigated site showed that the growth of the investigated species is limited by phosphorus. The significant positive interactions between P-N, P-K and NPK suggest that N and K would come second in limiting the growth of C. senna (L.) after P.