Abstract:
An adequate knowledge of the chemical reactions which occur when fertilizer is placed in soils is a pre-requisite to the development of sound fertilizer practices. Without such a knowledge, there is the possibility of applying either too much or too little fertilizer than is necessary with its consequent crop failure. Phosphorus is one of the major nutrient elements required by plants for growth. The role of phosphorus in plant nutrition includes its effect on cell division, flowering, fruiting and seed formation, crop maturation, root development, especially of lateral and fibrous rootlets, strength of straw in cereals, and crop quality of vegetables.
The problem of phosphorus deficiency in Ghanaian soils and its attendant low crop -yields has long been recognized by many research workers. Between 5,0 ppm and 14.5 ppm
phosphorus has been found in the topsoil CO" " 6 ") of many forest profiles in Ghana (Hardy and Amoroso-Centeno 1938;
DeEndredy and Montgomery 1954; Nye 1952). Using Bray's rapid extraction procedure with 0,TN. HC1 and 0.03N NH^F Nye
(1952) obtained 4 ppm phosphorus in the topsoil (0" - 6") of sixty-three soils from savanna sites in Ghana, In spite of these very low value o-f available phosphorus in Ghanaian soils, Nye (1952) reports that response to phosphorus application has not been always conclusive. This lack of response has often been attributed to the high fixation capacity of tropical soils, especially the strong acid ones with high content of iron and aluminium rendering small dressings of phosphate ineffective.
Several observations made by agronomists the worldover on crop response to applied phosphate give credence to those made in Ghana, These indicate that fertilizer phosphate after it has been applied is not recovered wholly in the crop that is immediately planted. Hemwall (1957) in a review, reports that crops recover only 10 to 301 of applied phosphorus, Sauchelli (1965) also reports that plants on phosphorus-fertilized soils generally recover just
20 to 30% of the added phosphate. The general consensus among soil chemists is that chemical precipitation and colloidal adsorption are chiefly responsible, for the loss.
As indicated earlier on, most Ghanaian soils are deficient in phosphorus and yet would not give any response to applied phosphorus fertilizer. Investigation by many research workers have also proved the methods of assessing the availability of phosphorus quite inadequate. We therefore propose to tackle the problem of phosphorus availability studies from another angle.
