The effect of times of contact and rates of minjingu phosphate rock (mpr) on its dissolution in an oxic (kanhaplic) haplustults
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Date
2001
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Sokoine University of Agriculture
Abstract
An incubation glasshouse pot experiment was conducted at the Sokoine University of
Agriculture Morogoro, Tanzania to study the effect of time of contact and rates of
Minjingu phosphate rock (MPR) applied to an Oxic (Kanhaplic) Haplustults on its
dissolution and the release of P and Ca for plant uptake. The soil was mixed with MPR
at rates equivalent to 0, 50, 75, 100 and 150 kg P/ha. The incubation periods were 120,
90, 60, 30 and zero days prior to sowing the maize (Zea mays. L. var. Staha). The
moisture content in the soil was maintained at about field capacity during the incubation
period and throughout the maize growing period with distilled water. Results from this
study showed that MPR dissolution increased significantly with increase in MPR rates
and incubation period. However, the increase in the amounts of P released tended to
increase with time of incubation up to about 75 days and decreased thereafter.
Presumably the P released was largely sorbed by Al and Fe oxides in the soil. The
amounts of MPR dissolved ranged from 1.17 to 13.11 mg P/kg and 10.74 to 15.91% as
regards to extractable P and AP% values, respectively. The interaction between
equilibration periods and MPR rates explained about 86.8% of the variation in MPR
dissolution, MPR rates predicted about 76.6% of the dissolution of MPR, and 10.3% of
the dissolution predicted by equilibration period. The soil pH and extractable Ca were
found to increase slightly with increase in MPR rates but decreased with increase in
incubation period. The exchangeable acidity and exchangeable Al decreased with
increase in MPR rates, and slightly increased with increase in incubation periods. Maize
dry matter yields, P and Ca uptakes were found to increase significantly with increase in MPR levels. Elemental P and Ca contents in the plant materials were found to decrease
significantly with the increase in MPR rates probably indicating the effect of dry matter
yield on nutrient dilution or depletion of phosphate and Ca2+ in the soil. Application of
MPR at sowing time led into higher dry matter yields than when applied prior to sowing
and increase in incubation period decreased the uptakes of P and Ca though inconsistent
with %P and %Ca in the plant shoots. Application of MPR at sowing time was
recommended for Oxic Haplustults which are strongly acid, with low amounts of P and
exchangeable Ca in order to increase the agronomic effectiveness of MPR.
Description
Masters' Theses
Keywords
Minjingu phosphate rock, Oxic (kanhaplic), Haplustults