RELATIONSHIP BETWEEN THE PHOSPHORUS BALANCE OF HUNGARIAN LONG-TERM FIELD TRIALS, TREND OF YIELDS, AND SOLUBLE PHOSPHORUS-CONTENT OF THE SOILS

The long-term changes in the first 20 years of the Hungarian National Long-Term Fertilization Trials were studied. Eleven treatments were se lected for the study: unfertilized control, a large dose of fertilizer s [250-66-80 kg/ha of nitrogen (N), phosphrous (P), and potassium (K), respectively], and all combinations of 50-100-150 kg/ha N and 0-22-44 kg/ha P with 80 kg K/ha. Three experiments, started in 1967, 1968, an d 1969, consecutively, were included in the analysis with same crop ro tations of wheat-maize-maize-wheat. Positive linear trends in yields w ere seen over the course of the experiment, even on the unfertilized p lots. Nitrogen and P fertilization had strong influences on the slopes of trends. Ammonium lactate-soluble P content in the soil plough laye r also increased if P fertilizer was applied. Linear trends of nutrien t content on yield were also seen in some treatments: positive for N a nd both negative and positive for the P. Nitrogen uptake increased in every treatment even in the unfertilized one. Phosphorus uptake increa sed at the higher P supply (44 kg P/ha). Phosphorus input was approxim ately equal to output at the 22 kg P/ha level, although the soluble so il P content increased at aproximately 10% of the fertilizer input.