P-EFFECTS AND AFTER-EFFECTS ON CHERNOZEMI C BROWN FOREST SOIL

A long-therm fertilizer experiment was set up by Mihaly Kramer in 1958 on what was originally an eroded chernozemic brown forest Martonvasar soil with ''very poor'' P supply. After modifying the treatments, fro m 1975 the after-effects of the ''old'' phosphorus remaining in the so il and the effects of annual P fertilizer in a maize-winter wheat dicu lture were compared in 5 fertilizer cycles. The structure of the exper iment also made it possible to study the P response modifying effect o f 40 t/ha farmyard manure applied in the first year of the cycles. Gro uping the experimental plots according to their carbonation, the ''fre sh'' P effect of different lime states and their P after-effect modifi cation were investigated. On the control plots the AL-soluble P2O5 con centration of the cultivated layer did not change even after 36 years. Manure application increased the AL-soluble P2O5 content of the plots by 60 ppm by the end of cycle IX uniformly, but this only led to a si gnificant yield increase compared to the untreated control. Similarly to earlier studies, the different lime contents of the experimental so il could not be revealed in the quantity of the grain yield of the tre atments with fresh P application, however due to the different yield l evels of the P unfertilized control plots higher P effects were measur ed on the more carbonated soils. The P after-effect of plots with lowe r lime content (1-5 CaCO3%) equalled the effect of the ''fresh'' P eve n after 5 fertilizer cycles. In the case of plots with more carbonate (5-15 CaCO3%) the yield increasing P after-effect ceased, indicating t hat a part of the P given into the soil had changed into a less availa ble form.