Farmyard manure application in weathered upland soils of Madagascar sharply increase phosphate fertilizer use efficiency for upland rice

A vast upland area in Madagascar remains uncultivated because of erratic rainfall and because of the low fertility of the soils that are highly weathered and depleted in available phosphorus (P). This study was set up to identify to what extent farmyard manure (FYM) can overcome P deficiency and increase the use efficiency of mineral P (TSP). Rainfed rice was grown with soybean in rotation (two fields) in three subsequent seasons with factorial supplies of FYM and TSP (both applied in planting hole) with blanket N&K doses. The low and unresponsive rice grain yields (< 2 Mg ha(-1)) in the initial year were contrasted with large treatment responses cumulating in a grain yield of 5.8 Mg ha(-1) in year 3 at highest rates, 3.6-fold above the no P and no FYM control with N&K and 11-fold above the absolute control. The above ground P uptake responded to total P application (TSP and FYM derived) and its slope significantly increased with FYM application. The fertilizer (TSP) P use efficiency in the above ground biomass, was 14% for the zero FYM dose increasing to 22% for the highest FYM dose of 10 Mg ha(-1) at year 3 of study. The FYM benefits were likely unrelated to nutritional factors as revealed from tissue analyses and it is speculated that FYM alleviates moisture stress or Al toxicity. Dosing FYM only with no TSP did not alleviate P deficiency. This study illustrates the agronomic potential of the uncultivated area provided that the soil nutrients are capitalized.