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/hm 2 in 1995 and 1996 were studied using a mass-balance a...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/hm 2 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/hm 2 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 under field conditions. Based on the mass-balance principle, at least 10 kg S/hm 2 per year may be necessary for sustainable development of grazing system.展开更多
文摘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/hm 2 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/hm 2 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 under field conditions. Based on the mass-balance principle, at least 10 kg S/hm 2 per year may be necessary for sustainable development of grazing system.
