The effects of poultry manure and its chemical constituents on rock phosphate solubility
Phosphorus inputs are essential to achieve satisfactory levels of crop production in many parts of the world. In this context the use of rock phosphate is an attractive option because it is considerably cheaper than water-soluble traditional commercial P fertilisers. However, the low solubility of rock phosphate is the major limitation to its use specially for short growing crops such as rice, potato and vegetable crops. This thesis investigates the potential of poultry manure as a viable management option to increase the solubility of rock phosphate. A conventional pot experiment with dwarf French bean (Phaselus vulgaris) was conducted with 2 sources of rock phosphate, namely Eppawela rock phosphate (Sri Lanka) and Gafsa rock phosphate (Tunisia). Three different rates of rock phosphate (37.5, 75 and 150 kg P2O5 ha-1) and poultry manure (75 kg P2O5 ha-1) were combined in a factorial experimental design. Two different planting systems were imposed to investigate the effect of fallow periods and the presence of the crop on rock phosphate solubility. The solubility of rock phosphate was evaluated in terms of various parameters including plant growth, P uptake and changes in the soil P status. The application of poultry manure when combined with rock phosphate increased plant growth, P uptake and soil extractable P compared to the calculated combined individual effects of the inorganic and organic fertiliser. In addition, other parameters, such as plant Ca, N and K uptake and various soil parameters also increased in response to mixing rock phosphate with poultry manure. The same experiment was used to study solute losses. The loss of PO4-P, NO3-N, NH4-N, Ca and K was increased by the addition of poultry manure with the highest losses observed during the fallow period compared to the cropping period. The leaching of PO4-P into the drainage water increased after harvesting of bean crop. Inorganic P was the major P fraction lost into drainage water.