No abstract

During recent decades the problem of the sulphur cycle in the agroecosystem has become increasingly urgent due to the improvements in agricultural technologies and reduction of environmental pollution. The extremely moist climatic conditions prevailing in Lithuania predetermine rather significant losses of sulphur by leaching and also its negative balance. Thus, sulphur deficiency may become a limiting factor in crop productivity in both organic and intensive cropping systems. This paper summarises the results of investigations on sulphur migration and balance in Luvisols carried out from 1994-1998 under both cropping systems. In an intensive cropping system with programmed mineral fertilization the yield of all crops was 54% higher compared to the organic one, where only manure was applied. Liming, used as a means of chemically improving soil, not only neutralizes soil acidity, but also its sulphureous regime. The amount of mobile sulphur in soil is reduced by up to 7-8 times by this treatment. This reduction is even more evident in intensive cropping systems. Mineral fertilization is the main means of regulating nutrient balance. The balance of N and P was negative in organic cropping systems. In contrast, it was positive under the conditions of intensive cropping. Neither the organic nor the intensive cropping systems ensured a positive sulphur balance. The average annual sulphur deficit was 91 kg ha À1 in intensive cropping systems and rose even to 142 kg ha À1 in organic cropping systems. In order to avoid sulphur deficiency as a factor limiting crop productivity and to ensure a positive balance of sulphur in agroecosystems, additional usage of S-rich fertilizers is a necessary condition for rationally farming Lithuanian acid soils.

The current investigation compared various intensive crop rotations (Norfolk, row crops, cereals, short-term grass) grown on Cambisols. The results showed significant effects of N fertilization on the agroecosystem and N balance, and on the mineral N concentration in drainage water and its leaching process. The highest N concentration in drainage water and leaching was determined in the cereals and row crops rotations. No major impact of the crop rotation on the P-PO 4 3Ϫ concentration in drainage water was determined. The average leaching of P-PO 4 3Ϫ by drainage did not exceed 100-140 g ha Ϫ1 within a seven-year study period. A rational and well-considered fertilization regime ensures high crop productivity and profitable farming as well as a steady, close-to-neutral N balance, which is the main condition for reducing the non-point source pollution of water.