半干旱草原栗钙土土壤硫素与群落放牧演替关系的研究

The sulphur (S) is a major plant nutrient and S deficiency was reported worldwide. Next to plant growth S deficiency has a strong impact on animal performance. Sheep are more sensitive than cattle to S deficiency because of their intensive S requirement for wool production. The improvement of the S nutritional status of forage crops had beneficial effects on animal performance. Grassland-livestock is the main agricultural activity in Inner Mongolia steppe of China. The pastoral system is characterized as a system with soils, forage, ruminants and manure as main components, and in such a system, nutrient cycling is very important to maintain soil fertility and optimize forage and animal production Severe S deficiency is an increasing nutritional problem in China, due to increasing productivity levels and input of S-free fertilizer. However, little is known about the S status of forage crops and soils in the Inner Mongolia steppe. S requriements and factors that influence sulphur availability to ruminants fed forage diets are poorly defined in Inner Mongolia steppe. Therefore the objective of this study was to determine: 1) sulphur status of forage plants and soils and to evaluate sulphur nutrition of grazing animals in the Inner Mongolia steppe; 2) the influence of N and S fertilization on yield, quality of spring oats, and metabolism of N and S by sheep in Inner Mongolia steppe of China; 3) the principle of S budgets used to evaluate effects of S fertilizer on the major progresses of S cycling.The results showed that the sulphur status on 4 soils and 122 typical plants from Inner Mongolia steppe were determined and evaluation was made for surphur nutrition of grazing animals. The results showed the organic sulphur content ranged from 17 μg g-1 in the 0.2~0.4 m soil layer to 397μg g-1 in the top soil. The mean sulfate-S concentrations were less than 10μg g-1; greater concentrations were found in only the chernozem soil. Biomass-S accounted for 1.78%~2.80% of total S in 4 soils. 75% of plant samples examined had less than 0.16% S, and more than 80% of them had an N:S ratio greater than 14:1. More than 80% of the plants were deficient in S. There was a close relationship between plant available soil sulphur and total plant sulphur concentrations. It was concluded that sulphur deficiency is widespread in the Inner Mongolia steppe and that sulphur fertiliser requirements should be evaluated.Under S deficiency, S and N fertilization increased dry matter (DM) yield of spring oats, but interaction between N and S was not observed. S fertilization increased S content and decreased significantly N:S ratio. There was a significant interaction between N and S on N content of the oats. N and S fertilization increased DM apparent digestibility of oats, but did not affect oats intake of metabolic body of lambs (g/kg BW0.75). N increased average daily gain of lambs with S supply as 1.5 times as that without S supply, but interaction between N and S was not observed. S intake, urinary S excretion, S absorbed and S retained of lambs were linearly increased by S fertilization. S fertilization increased N utilizational efficiency of oats and vice versa; and N retained was affected by interaction of N and S fertilization. N:S ratio of oats was positively correlated with N metabolism. . The critical levels of total S were 0.20% and 0.23%, and N:S ratios were 17.0:1 and 15.7:1 for maximum DM and CP yield of oats, respectively. And the critical levels of S content and N:S ratio in oats for maximum average daily gain of lambs were 0.26% and 10.5:1, respectively. Therefore, in the diagnosis of S status in soil-forage-animal system, it is considered that the use of total S and N:S ratio in the forage for the maximum CP yield is prefer to that for the maximum DM yield. The concentration of plant S required for maximum performance of lambs fed oats hay was higher than that required for maximum CP yield of the oats..Results indicated that S fertilizer increased by 50% of herbage S uptake and 15% or more of S bio-cycling rate in grazin

S是植物和家蓄必需的营养元素之一。土壤硫水平、分布及转化过程与土壤有机C、N、P、微生物活性和植物吸收能力密切相关，反过来又影响植物间的关系和群轮动态。通过定量研究半干旱草原硫的空间分布、转化和对植物的影响，以及放牧梯度下植物群落与土壤的分布，为理解半干旱草原群落结构和放牧演替机制、为草地生态系统可持续发展提供依据。