ACCUMULATION AND MOBILIZATION OF PHOSPHAT E IN HAPLIC CHERNOZEM OF THE STATIC LONG-TERM EXPERIMENT AT LAUCHSTADT - CONSIDERATION OF THE P-BALANCE AFTER 84 YEARS

Phosphate balance was calculated ad various soil P parameters of a lon g-term field experiment at Lauchstadt were determined in which mineral fertilizer and farm yard manure were applied in rates of 0 to 54 kg P /ha/year. The various fertilizer treatments resulted in a considerable variation of the P balance sheet ranging from -738 to 2652 kg P/ha. T his implies that 59% of the applied P (cumulated maximum 4477 kgP/ha) remained in the soil, the rest was taken up by crops. Assuming a balan ced P supply in which crop P uptake equaled the P fertilizer rate, a r ate of 12,9 kgP/ha/year would be required. This rate was approximately calculated for the various treatments having received farm yard manur e. Phosphate mobilized from the soil (up to 738 kg P/ha) was related t o factors which had an impact on crop yield. The decrease of total P i n the upper soil layer (0 to 25 cm) was lower than the cumulative P up take of crops. It is therefore assumed that a considerable proportion of P taken up by crops came from the subsoil. The change in the P bala nce sheet obtained during 84 years was clearly reflected by various so il parameters including the maximum P adsorption capacity which was hi ghest in the treatment with the largest P deficit (NK treatment).