Effectiveness of topdressed and incorporated superphosphate and Duchess rock phosphate for subterranean clover on sandy soils near Esperance Western Australia

Abstract

In 2 experiments on sandy soil near Esperance, W. A., superphosphate and Duchess (Queensland) apatite rock phosphate were either left on the soil surface after application (topdressed) or incorporated into the top 10 cm of the soil with a rotary hoe (incorporated). One experiment was on Fleming gravelly sand which had a greater capacity to adsorb phosphorus than did the deep yellow sand (Gibson sand) used in the other experiment. Dry matter or seed yield of subterranean clover and phosphorus content of dry herbage or seed were used as indicators of the effectiveness of the phosphorus treatments. Compared with topdressed superphosphate, incorporation of superphosphate did not greatly influence its effectiveness on the Gibson soil, but reduced its effectiveness by about 20% on the Fleming soil. Relative to topdressed rock phosphate, incorporation of rock phosphate almost doubled its effectiveness on the Fleming soil, and improved its effectiveness by about 1.5 times on the Gibson soil. Superphosphate was the more effective fertiliser. Relative to topdressed superphosphate, the effectiveness of topdressed and incorporated Duchess rock phosphate, respectively, was about 15 and 30% on the Fleming soil, and about 25 and 40% on the Gibson soil. There was no evidence of any leaching of phosphorus from Duchess rock phosphate from the 0-10 cm layer of either soil, nor of superphosphate on the Fleming soil. However, on the Gibson soil, there was some leaching of superphosphate to below 10cm, but not below 20 cm.