SULPHUR MINERALISATION IN FIVE DANISH SOILS AS MEASURED BY PLANT UPTAKE IN A POT EXPERIMENT

摘要

Reductions in atmospheric S deposition have created S deficiency in some agricultural soils. In such soils the release of S from organic matter may be important for the supply of S to plants. In this study net mineralisation of S was measured during two successive growth seasons as S removed by plant material and leachates. Pots were subjected to natural conditions and cropped with either Italian rye grass (Lolium multiflorum Lam.) both years or spring oilseed rape (Brassica napus L.) followed by spring barley (Hordeum vulgare L.). Sulphur was the limiting factor for dry matter yield in the pots. Sulphur concentrations in Italian rye grass, rape and barley varied from 0.055 to 0.21, 0.06 to 0.078 and 0.07 to 0.17%, respectively. Net mineralisation was 3.3-6.7 mu g S per g soil year(-1) (1.7 to 3.1% of total organic S), and could not prevent S deficiency in the crops; differences among soils developed early in the experiment. Net mineralisation of S was not significantly correlated with total organic S, C-bonded S or sulphate-ester S content of the soils but with microbial activity in the soils (r=0.90). Net mineralisation was significantly affected by the type of cropping system but differences between systems were small compared to differences in net mineralisation among soils. It may be concluded that reductions in atmospheric deposition of S must, at least partly, be replaced by S fertilisation to maintain crop yield and quality.