(a) Szilas(i), J.M.R. Semoka (ii) and O.K. Borggaard(i)

(i) Chemistry Department, The Royal Veterinary and Agricultural University, 40 Thorvaldsensvej, 1987 Frederiksberg C, Denmark

(ii) Department of Soil Science, Sokoine University of Agriculture, P.O. Box 3008, Morogoro, Tanzania

Received: 21 June 2006 Accepted: 26 December2006 Published online: 25 January 2007

Abstract - “A compilation of all presently available agronomic data on the Tanzanian Minjingu Phosphate Rock (MPR) has shown to be a valuable tool for evaluating the interactions between tropical soils and MPR or Water Soluble P (WSP) sources. The effect of a delayed dissolution of MPR products compared to MPR with the yield response to WSP showed that, in the first 2 years, the average effectiveness of MPR is 74 and 94% of WSP respectively, whereas from the third year onwards the relative effectiveness is around 104%. From the analysis of the effect of soil properties on the yield response, it was found that low soil pH and low amounts of available P are the most favorable conditions for effective use of MPR. However, beneficial effects were also indicated on less acidic soils if they are strongly P deficient. MPR application seems to have superior effect on soil properties such as pH, exchangeable Ca and Al compared with WSP. The effect of MPR application on available P and Na OH extractable P is significantly lower compared with WSP but the difference seems relatively small. An estimation of the distribution of the cultivated area of Tanzania into four suitability classes for direct application of MPR seems to be a useful tool in the process of selecting target areas where direct MPR application should be promoted”.

( J.M.R. Semoka <jsemoka@suanet.ac.tz>) et. al