DYNAMICS OF SOIL AVAILABLE S IN WHEAT MAIZE ROTATION OF BEIJING

Dynamics of available sulphur in soils of wheat maize rotation system was studied by microplot experiments in Beijing suburban. The results showed significant seasonal changes of soil available sulphur during wheat and maize growth periods. The degree of seasonal variety of available suphur in soil profile declined from surface to 60cm in depth. This was largely explained by dry and wet deposition, rainfall, irrigation, crop uptake, and leaching. Available sulphur concentration decreased downward from top layer in soil profile in wheat soil. And this kind of distribution pattern did not change during wheat growth. However, available S in 0～20cm layer decreased steadily during maize growing season and it changed from the highest in early season to the lowest of the three layers (0～20cm, 20～40cm, 40～60cm) in the end. It was suggested that a great amount of soil available S be leached during this period of time. The same trend was found in exurb fields except for lower content and smaller seasonal variation.