Can local Minjingu phosphate rock replace superphosphate on acid soils in Tanzania?

Locally occurring Minjinju phosphate rock (MPR) in direct application as P source for maize production was compared with water-soluble imported, processed triplesuperphosphate (TSP) in a field study over three seasons on ten important, low-fertility agricultural soils throughout sub-humid to humid Tanzania. Except for the first season, where MPR was slightly inferior to TSP, direct application of MPR gave the same yields as TSP indicating that MPR can replace TSP on acid, severely weathered tropical soils low to very low in available P and exchangeable Ca and with high to very high phosphate adsorption capacity. Similar response for granulated and non-granulated MPR enables replacement of the dusty finely powdered MPR by the user-friendly granulated form. However, P fertilization improved maize yields on only three soils because plant growth is also limited by other factors than P, such as frost (one site) and lack of water and other nutrients, e.g. B, Cu and Mg. Apart from saving foreign currency, replacement of TSP by MPR has additional advantages because MPR contains calcium carbonate (lime effect), Mg, K, Cu and Zn. On the other hand, economy constrains MPR use as MPR was found to be economically competitive with TSP only in areas within about 700 km from the mine, mainly because of current very high transportation costs.