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 Togophosphate rock and ammonium sulphate soil amendment. Treatments were preparedthrough 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+2gAS, 25.0g PR+1g AS and 25.0g PR+2g AS kg-1 soil. Standard laboratory methods were usedto assess pH, available phosphorus (P) and total phosphorus (P). Generally, the pH oftreatments 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 thosewithout. Amendments with the 2gAS kg-1 soil had significantly (p≤0.05) lower mean pHvalues than those with the 1gAS kg-1 soil. The AS fertilizer treatments also hadsignificantly (p ≤ 0.05) higher levels of the available P than those without. The higher theamount 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 theavailable P released. The peaks of available P released were observed between the 6th andthe 8th weeks, after the lowest pH values had been attained. Decreased soil pH relativelyincreased the amount of phosphorus released (y = -12.47x + 111.4; R2=0.53). Addition ofPR in the treatments increased the total P levels. In conclusion, combined application of ASand PR has the potential to increase soil P availability, which is beneficial to crop farmers.