On-farm trials were carried out in the Operation Haute Vallée project, Mali, to assess the possibility of replacing, partially or entirely, imported cotton fertilizer with natural rock phosphate from a local source, and to assess the residual effect on maize and sorghum grown after cotton. The maize/cotton sequence, although not normally used by Malian farmers, was more profitable than either pure cotton grown alone or a cotton/maize sequence when local rock phosphate was used instead of imported fertilizer.