INORGANIC AND ORGANIC-P IN SOIL SOLUTIONS FROM 3 UPLAND SOILS .2. EFFECT OF DEFOLIATION AND FERTILIZER APPLICATION

The effects of defoliation and NPK fertilizer addition on the amounts of inorganic orthophosphate (P-i), organically combined phosphorus (Po-), total phosphorus (P-t) and the residual fraction P-r = P-t - (P-o + P-i) in soil solution from three P-deficient Cambisols with grass/clover swards were determined. The defoliation treatments, carried out in the first year, were regular cutting every 2-4 weeks to 2 cm, and cutting at the end of the growing season. The fertilizer treatments, applied in the second year, were 25 g m(-2) of 25:5:5 and 20:10:10 NPK fertilizer. In both years, soil solution was also taken from bare soil plots. Defoliation influenced the concentration of P-i, P-o, P-r and P-t in soil solutions, which mostly increased in the order no cut > cut 2 cm > bare soil treatment. Fertilizer additions increased dry matter production, and the amount of P in the crop, but had relatively little influence on soil solution concentrations of P-i, P-o, P-r and P-t compared with the previous year. There were no significant differences in either dry matter production, P uptake or the P-i, P-o, P-r and P-t, concentrations of soil solution between the plots receiving 25:5:5 or 20:10:10 fertilizer treatments. Phosphorus in soil solutions from the most acid of the three cropped soils was significantly correlated with Fe during August and October, The linear correlation coefficients (r) between Fe and P-i, P-o or P-t were between 0.73 and 0.94.