Saturday, 15 July 2006

Soil Quality.

Richard Doe, Univ of Cape Coast, P.o Box W J 333 weija, Accra, Ghana

Determination of phosphorus in soils has received extensive research attention from soil chemists because of the importance of Phosphorus in soil fertility management. Phosphorus is present in both organic and mineral form. The amount of inorganic phosphorus in the soil is a function of the parent material, crop variety, soil management and climate. The form of phosphorus is however is related more to the weathering of the soil. The different forms of phosphorus in soils have led to the conclusion that different phosphorus extract are desirable in different soil types. The general problem of phosphorus fertilization on Ghanaian Agriculture is the low available phosphorus content s in Ghanaian soils, inadequate mineral fertilizer application of rock phosphate as a result of poor Reactivity except in Acid soils. From the economic point of view, the following strategies may be taken to alleviate Phosphorus availability problems to small-scale farmers: (i) A joint venture could be established among Governments owning Phosphorus rock for consumption. (ii) Composting of organic wastes with less soluble rock phosphate to enhance solubility of phosphorus for plant use should be intensified. This Process will prevent precipitation of Phosphorus by Iron and Aluminium compounds. Soils from the wet and coastal areas of Ghana were sampled. Two different extraction procedures: NH4F and HCl was used to extract available phosphorus from the samples. The extrant was then analysed for soluble phosphorus and results were correlated with actual uptake of Phosphorus by the plant from a Greenhouse Experiment. The results of the study showed that soil reactions, types of clay minerals, soil temperature and reaction time, cation and anion effect and fertilizer phosphorus management affected the availability of phosphorus for plant uptake. The results further suggested that optimum application of phosphorus supplied to the plant is needed for plant growth and that the phosphorus content in Ghanaian soils is very Low. This implies that, Plants, which are phosphorus responsive, are dying out of the system due to depletion of phosphorus fertilizers for example coffee. Most Ghanaian soils contains high Aluminium and Iron oxides, when these oxides react with soluble phosphorus, Aluminium forms hydroxyphosphates and Iron hydroxyphosphates which are insoluble to plant roots, hence making the plant phosphorus deficient. To correct this, Liming is done to raise the pH of the soil in order to get rid of aluminium and iron to make phosphorus available to plants for use, thereby increasing cost of Agriculture Production. The type of clay minerals in most soils (Ghanaian) are made up of 2:1 clay minerals which have less phosphorus in them, therefore making most soils deficient in Phosphorus. From the analysis, it is clear that Phosphorus, as plant food is deficient in most Ghanaian soils. Against this background, supplements of phosphorus fertilizers and crop plant varieties, which grow in less phosphorus soils, must be modified for use.

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