Phosphorus release dynamics under phosphate rock and ammonium sulphate in soil amendment

Abstract

This study was undertaken to assess the release pattern of available phosphorus in a Togo phosphate rock and ammonium sulphate soil amendment. Treatments were prepared through the combinations of soil, phosphate rock (PR) and ammonium sulphate (AS) fertilizer. The treatments were; Control, 12.5g PR, 25g PR, 12.5g PR+1g AS, 12.5g PR+2g AS, 25.0g PR+1g AS and 25.0g PR+2g AS kg-1 soil. Standard laboratory methods were used to assess pH, available phosphorus (P) and total phosphorus (P). Generally, the pH of treatments decreased to the lowest levels between the 4th and 6th weeks after amendment. The AS fertilizer treatments had significantly (p≤0.05) lower pH values than those without. Amendments with the 2gAS kg-1 soil had significantly (p≤0.05) lower mean pH values than those with the 1gAS kg-1 soil. The AS fertilizer treatments also had significantly (p ≤ 0.05) higher levels of the available P than those without. The higher the amount of the AS in the amendment, the higher the level of the available P concentration. Increase in the level of AS in the amendment also increased the mean value of the available P released. The peaks of available P released were observed between the 6th and the 8th weeks, after the lowest pH values had been attained. Decreased soil pH relatively increased the amount of phosphorus released (y = -12.47x + 111.4; R2=0.53). Addition of PR in the treatments increased the total P levels. In conclusion, combined application of AS and PR has the potential to increase soil P availability, which is beneficial to crop farmers