Abstract
Phosphorus deficiency affects around 80% of the acid soils of western Kenya, but fertilizer use is limited due to high prices. This paper explores the potential of local phosphate rocks (PR) as a remedy within the context on an integrated soil fertility management approach. A promising phosphate rock is Minjingu PR (MPR, Tanzania), a sedimentary/biogenic deposit which contains about 13% total P and 3% neutral ammonium citrate (NAC) soluble P. On-farm trials in P-deficient soils in western Kenya demonstrate MPR to be as effective as triple superphosphate (TSP, 20% P) at equal P rates. The benefits are most pronounced with the integration of agroforestry technologies that improve soil fertility. Besides Minjingu PR, Busumbu PR from Uganda (BPR) is potentially another source of P. It is typical of the abundant but unreactive igneous PRs in eastern, central and southern Africa. Agronomic performance of BPR is poorer, though its lower cost and location near to P-deficient areas in western Kenya make it attractive in some situations. The policy implications of these findings are discussed further in the paper.
Highlights
Soil fertility depletion in smallholder farms is the major biophysical root cause for the declining per-capita food production in most of sub-Saharan Africa (Sanchez et al 1997)
Options to replenish soil P include the use of Minjingu phosphate rocks (PR) from northern Tanzania
This sedimentary PR with 70 to 75% relative agronomic effectiveness (RAE) is suitable for direct application in the P deficient acidic soils of western Kenya and is estimated to cost about 24 to 45% less than P from triple superphosphate (TSP)
Summary
Soil fertility depletion in smallholder farms is the major biophysical root cause for the declining per-capita food production in most of sub-Saharan Africa (Sanchez et al 1997). This is attributed to inputs of nutrients not exceeding losses, especially with harvested products. Population growth coupled with reduction in farm sizes has resulted in less land available for food production. After P and N deficiencies are overcome, K limits maize growth in about 25% of the area
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