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

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 4 th and 6 th 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 6 th and the 8 th weeks, after the lowest pH values had been attained. Decreased soil pH relatively increased the amount of phosphorus released ( y = -12.47x + 111.4; R 2 =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.