Sulphur (S) cycling and implications on S fertilizer requirement in sheep grazed pastures receiving three levels of S fertilizer at rates of 0, 30 and 60 kg S/hm2 in 1995 and 1996 were studied using a mass balance approach which accounted both for S inputs to and outputs from the soil plant animal system. Results indicated that S fertilizer increased by 50% of herbage S uptake and 15% or more of S bio cycling rate in grazing system. The total S recovery of 30 and 60 kg S/hm2 treatments from 1995 to 1996 was 74.0% and 37.6% respectively. Mineralization of organic S may be an important source of S for pasture when other S sources are low, accounted for 70% of the total S inputs without S fertilizer. The grazing sheep has an important ecological function, the feature of S cycling in grazed pastures was that 90% of herbage S ingested by grazing sheep was returned to soils as excreta. The amount of S released by sheep excreta accounted about 30% of the total released S through S bio recycling.Loss from soil S leaching beyond the major plant rooting zone was the main S output from grazing system. However, urinary and fecal S losses, including transfer and leaching losses, also affected S budgets of grazing system. It is therefore important to investigate the recycling rate of both urinary and fecal S underfield conditions.Based on the mass balance principle, at least 10 kg S/hm2 per year may be necessary for sustainable development of grazing system.
施硫肥对内蒙古典型草原放牧生态系统硫循环的影响及硫肥需要量的研究
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