Strategies for establishing adequate phosphorus levels in three soils with different phosphorus fixing capacities
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Date
2004
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Sokoine University of Agriculture
Abstract
A study was conducted under pot and field conditions to establish adequate levels of
phosphorus in three soils with different P fixing capacities. These soils were from
Magadu, Morogoro District, classified as Oxic Haplustidt, Sasanda, in Mbozi
District, classified as Drystropept and Nkundi in Nkasi District, classified as
Acruoxic Kancliustult. A pot experiment was conducted at SUA- Department of Soil
Science while field experiment was carried out at Sasanda in Mbozi District in
Mbeya region. The treatments were 0, 40, 80 and 160 mg P/kg of soil for Nkundi, 0,
100, 200 and 400 mg P/kg of soil for Magadu and 0, 800, 1600 and 3200 mg P/kg of
soil for Sasanda soil. For field experiment the treatments were 0, 800, 1600 and 3200
kg P/ha. The sources of P were TSP and MPR. There were seven treatments for field
and eight treatments for pot experiment. The experiment was laid out in a
Randomized Complete Block Design. The tested crop was maize {Zea mays var UH
615). The objectives of the study were to identify rates of P required for optimizing
maize dry matter grain yields, and associated available P levels in the soils. Results
of the study showed that, both TSP and MPR were effective sources of P in the soils
studied. Both TSP and MPR significantly (P = 0.05) increased DM and grain yield, P
uptake and available P over the control by 97.7, 95.8, 76,8 and 95.3%, respectively
in Sasanda soil. This was attributed to 95.3% increase in available P in the soil after
TSP and MPR application in Sasanda soil. This was supported by the highest grain
yield, DM yield, and P uptake of 2.97 t/ha, 64.18 g, and 124.8 mg/kg at the rates of
3200 kg P/ha and 3200 mg/kg, respectively in Sasanda soil. However, MPR was
slightly less effective than TSP for most of the aspects studied. The optimum rates
were 160, 200 and 3200 mg P/kg for Nkundi, Magadu and Sasanda soils, respectively under pots. However, these rates have to be confirmed under field
conditions. In Sasanda field experiment, P application did not significantly (P = 0.05)
increase available P and the available P was below the critical level. This was
attributed to high fixing capacity of the soil. The rale of 1600 kg P/ha gave the
highest grain yield of 2.97 t/ha in the current study. Results from the current study
indicated that MPR has the potential of supplying P for maize production therefore it
could be used as an alternative source of P to TSP. A large, one-time application of
P on highly P deficient soils is not always the solution for correcting P deficiency in
all soils like in Sasanda soil. A gradual seasonal P application might be the most
cost-effective approach for high P-fixing soils.
Description
Dissertation
Keywords
Sasanda- Mbozi district, Soils, Soil science