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/cl over swards were determined. The defoliation treatments, carried out i n the first year, were regular cutting every 2-4 weeks to 2 cm, and cu tting at the end of the growing season. The fertilizer treatments, app lied in the second year, were 25 g m(-2) of 25:5:5 and 20:10:10 NPK fe rtilizer. In both years, soil solution was also taken from bare soil p lots. 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 co mpared with the previous year. There were no significant differences i n 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 wit h 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.