The agronomic effectiveness of lime-reverted and dicalcic superphosphates: A review

Results from 10 field trials that compared the agronomic effectiveness of water-soluble phosphate (WSP) fertilisers with reverted or dicalcic superphosphates (DCP) are reviewed. The 51 observed relative responses ranged from +20% to -10%, with a mean response of 0.2%. Nineteen (38%) were positive and 22 (62%) negative. A total of 17 were statistically significant (P less than or equal to 0.05), either negative (8) or positive (9). The 51 observed responses were normally distributed about zero, consistent with the hypothesis that these products have no effect on plant growth over and above the effect of WSP and that the range in the observed responses simply reflected the underlying biological variation. There was evidence in one trial that DCP may be more effective than WSP in situations where significant phosphorus (P) is lost through leaching. On an acid soil, DCP was superior to WSP because of the free lime present in the former product. it is concluded that DCP have no effects on plant production over and above that which can be achieved by applying lime and WSP separately. It follows that the interaction of the two components that results in the process of reversion and the formation of less soluble DCP confers no advantage relative to the use of WSP.