THE EVALUATION OF THE RESIDUAL EFFECT OF FERTILIZER IN LONG-TERM FERTILITY PLOTS: II. PHOSPHORUS

Abstract

Long-term annual applications of fertilizer phosphorus to an acid sandy loam podzol resulted in marked increases in total phosphorus content of the surface soil. However, downward movement was limited as no increase occurred below 9 in. The relationship between total phosphorus content of the profile and sodium bicarbonate-soluble phosphorus (r = 0.93) was significant at the 1% level. Phosphate retention capacity of the surface soil was not influenced by fertilizer or manurial treatment and increases in percentage phosphorus saturation were relatively small.Under conditions of intensive cropping in the greenhouse (12 crops), residual phosphorus was highly effective in supplying crop requirements. However, the results suggest that fertilizer phosphorus may be beneficial during the establishment period. The relationship between phosphorus uptake on the no P series in the greenhouse and levels of sodium bicarbonate-soluble phosphorus (r = 0.88) is further evidence of the value of this method in estimating phosphorus availability in soils.