Subsurface transport of phosphorus through the soil
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Date
2013-08-01
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Abstract
Phosphorus (P) is critical to the production of crops in agriculture. But the strategies adapted to increase phosphorus capital P capital in the soil tend to neglect subsurface transport of P with the assumption that it is bonded strongly to soil particles and would therefore not be a threat to groundwater contamination. Discovery of high concentrations of P in ground and surface water has inspired investigations into factors that contribute to its transport. The study was conducted to determine the subsurface transport of P through soils under cocoa plantation and arable land. Soil samples were taken at a depth of 0-30 cm from two land-use systems namely, a cocoa plantation and an arable land under cultivation. The samples were air-dried and passed through a 2 mm sieve. The soil particles that passed through the 2 mm sieve were used for the transport experiments. Different rates of P were applied at 0, 69, 137, 206, 274 and 343 ppm. For macropore flow, pores were varied in depth (5, 10 and 15 cm), number (1, 3 and 5) and diameter (2, 4, 6 and 8 mm). The study showed that soil organic carbon (SOC) improved hydraulic conductivity of soils and enhanced their water flux density. The cocoa plantation was more liable to groundwater contamination than the arable land. The concentration of the discharged P effluents increased as the rate of P increased in soils under both land-use systems. This showed that massive application of P to increase “soil phosphorus capital” for plant uptake could increase the risk of subsurface loss of P from agricultural systems into both ground and surface waters. This could lead to environmental problems such as eutrophication of surface water. Macropore depth, number and diameter and their interactions significantly affected preferential flow of P. The contribution of the different macropore parameters to subsurface transport of P in both land-use systems were in the order depth> number> diameter. The impact of soil macropores on
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preferential flow of P was more profound in soils under the arable land as compared to the cocoa plantation. The study also showed that P solutions moving through the soil profile may enhance more P sorption at the upper horizons than the lower horizons.
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A thesis submitted to the School of Graduate Studies,
Kwame Nkrumah University of Science and Technology, in partial fulfilment of the requirement for the award of Master of Science
in
Soil Science, November, 2013