THE RELATIONSHIP BETWEEN SPECIES DIVERSITY AND NITROGEN CYCLING IN PASTURE

生物多样性的研究不仅对群落生态学，而且对应用生态学都具有重要意义。我们想知道生物多样性的程度是否会影响牧草氮循环的效率。许多科学家认为，生物多样性与生产之间有着密切的关系。如果生物多样性与生产力之间存在正相关关系，那么高生物多样性的生态系统具有较高的母体循环能力，如氮循环能力。氮素损失量由牛奶、肥料和饲料粮中的氮素含量计算，以考虑环境影响。为了测定牛尿中氮素对牧草生产的利用效率，我们用15 N标记牛尿进行了另一项试验，结果表明，低投入牧草的植物生长量高于高投入牧草。植物和土壤蜱类多样性之间有很强的相关性。单位牧场产奶量的成本效益分析结果表明，奶牛产奶量存在最优投入。许多农民将达到最佳点，这意味着牛奶生产的高效率。20年来，牧草氮素损失率由80%以上下降到50%，单位牧草产奶效率与牧草生物多样性呈正相关，用15 N标记法估算了牧草氮素从牛尿中的回收率为21.6%~ 39.4%。

The study of bio-diversity is very important for not only community ecology but also applied ecology. We want to know whether degree of bio-diversity affects efficiency of nitrogen recycling in a pasture or not. Many scientists said that there are close relationship between bio-diversity and production. If there are positive relationships between bio-diversity and production then the ecosystem of high bio-diversity have high ability of maternal recycling such as nitrogen recycling.Then we tried to the roll of bio-diversity in pasture by two aspects such as effects of management on bio-diversity, relation between bio-diversity and nitrogen recycling.Species diversities of plant and soil tick were measured by sampling data from each pasture. Nitrogen losses were calculated by nitrogen amount in milk, fertilizer and feed grains for environmental impact. To measure the efficiency of nitrogen recovery from cattle urine to grass production we used 15N marked urine in another experiment.The plant diversities of low-input pastures were higher than high-input pastures. There is strong relationship between plant and soil tick diversity. Results of Cost-benefit analysis for milk production per unit pasture show the presence of optimal-input for milk production. Many farmers will arrive to optimal point that means high efficiency of milk production. The nitrogen losses were decreased from over 80% to 50% during these 20 years.There is a positive relationship between efficiency of milk production per unit pasture and bio-diversity.We estimated the recovery % of nitrogen from cattle urine to grass growth using 15N-marker method ranged 21.6% to 39.4%.