Effect of Application of Basic Slag and Superphosphate on Herbage Yield and on Soil and Herbage Concentrations of Phosphorus in Organic Grassland

Abstract

The experiment was carried out at an organic farm in 1996 and 1997. The purpose of the experiment was to test the effectiveness of basic slag (7% P) as a P fertilizer on an organic perennial ryegrass/white clover sward. Superphosphate (16% P) was used as a standard comparison. There was no difference between fresh weight or dry matter yields of grass or clover or of total herbage yields in plots treated with different rates of basic slag or superphosphate in the first harvest at the end of July 1996. In the second harvest, recorded at the end of August 1996, increasing rates of P gave increased yields. P source had no effect on herbage fresh weight or dry matter yield. P source and rate of P application had no effect on herbage yield in 1997. The percentage dry matter in herbage was unaffected by P source. Increasing rates of basic slag and superphosphate had no effect on the percentage dry matter in the herbage. There was no difference in the soil P concentrations obtained with basic slag or superphosphate when these were applied at equivalent rates. Increasing rates of P, when applied as basic slag or superphosphate at rates of 7, 14 and 28 kg ha-1 , gave an increase in soil P concentration at 128 days after application. No increase was recorded at 531 days after application. Superphosphate gave the largest initial increase in herbage concentrations of P but was no more effective at raising the soil and herbage concentrations of this element than equivalent rates of basic slag over a two year period.