Long-term effects of land use and fertiliser treatments on sulphur transformations in soils from the Broadbalk experiment

Sulphur transformations were monitored in a unique set of arable, grassland and woodland soils from the Broadbalk Classical Experiment, which started in 1843. In an open incubation experiment with periodic leaching, 14-35 mg SO42--S kg(-1) was mineralised in 28 weeks at 25 degreesC, equivalent to 4.4-8.3% soil organic S. Cumulative amounts of S mineralised increased linearly during the 28 weeks, indicating constant rates of mineralisation. The rate of mineralisation was the greatest in the woodland soil (170 mug SO4-S kg(-1) day(-1)), followed by the grassland (120 mug SO4-S kg(-1) day(-1)) and the arable soil from the farmyard manure (FYM) plot (110 mug SO4-S kg(-1) day(-1)). Three soils from arable plots receiving different inorganic fertiliser treatments but no FYM had similar rates of S mineralisation (similar to 70 mug SO4-S kg(-1) day(-1)). an incubation experiment with 35SO(4)(2)(-), addition of glucose greatly enhanced S immobilisation. In 132 days, the woodland and grassland soils immobilised more S than the arable soils, with or without glucose amendment. Immobilisation and mineralisation of S occurred concurrently, and both were stimulated by glucose addition. The results show that S mineralisation and immobilisation were influenced strongly by the type of land-use and long-term organic manuring, whereas annual application of sulphate-containing fertilisers for over 150 years had few effects on short-term S transformations. (C) 2001 Elsevier Science Ltd. All rights reserved.