Abstract:

The majority of soils in Africa are P-deficient,
but the high cost of conventional, water-soluble P
fertilisers limits their use by resource-poor
farmers. Rockphosphates are a low-cost alternative. The relative agronomic effectiveness of
unacidulated (RP), 25% partially acidulated
(PARP25), 50% partially acidulated (PARP50)
Minjingu rockphosphate and triple superphosphate (TSP) was evaluated at rates of 0–80 kg/ha
P on stylo (Stylosanthes guianensis) on an Ultisol
in the Ethiopian highlands. The fertilisers were
applied once and their effects were followed for 4
consecutive harvests. Stylo dry matter (DM)
yields were below 3 t/ha at each cut without
applied P and reached as high as 4.8 t/ha when P
was applied. Over all 4 cuts, RP was 100%,
PARP25 was 89% and PARP50 was 103% as
effective as TSP in increasing stylo herbage
yields. The corresponding relative responses in P
uptake were 103, 79 and 92% for RP, PARP25
and PARP50, respectively. The substitution rates
for herbage yields were 100% for RP, 79% for
PARP25 and 106% for PARP50 while those for P
uptake were 106% for RP, 62% for PARP25 and
85% for PARP50. Significant (P < 0.05) effects
of P on stylo DM and P uptake were observed at
all harvests