Impacts Of Fencing On 'Black Soil Beach' Sowing Grassland In The Yangtze And Yellow River Regions

From 2006, fenced and to observ'eback soil beach'sowing grassland three years ago at the Yangtze and yellow River regions, sowing grassland for grazing in winter inside fence make contra,compared and analyzed the effect of fencing on grassland community characteristics, aboveground biomass and underground biomass,forage nutritive composition and soil nutrient, aimed to understand the effect of fencing on Elymus nutans grassland, The results showed:Before the fencing there were total 7 species, which belongs to 4 families and 7 genera in this plant community. In the first year of fencing there were total 14 species, which belongs to 9 families and 14 genera in this plant community. In the second year of fencing there were total 17 species, which belongs to 10 families and 17 genera in this plant community; In the grazing grassland, in the first year there were total 22 species, which belongs to 14 families and 21 genera in this plant community, in the second year there were total 30 species, which belongs to 16 families and 30 genera in this plant community. In three years the important value of dominant species on fencing and grazing grassland were respectively 50.6%,57.83%,48.86%和50.6%,38.27%,40.81%. After the fencing with the increase of grassland age, diversity index increased slowly and on fencing grassland there was bigger than on grazing grassland. In the first year of fencing the evenness index become litter, in the second year it become bigger, however it still smaller than before the fencing. And the dominance index of fencing grassland was smaller than grazing grasslandWith the increase of grassland age, the grassland production was descries slowly, The decline of fencing was more obvious, after fencing the proportion of standing dead litter and litter was become bigger and bigger, it seriously affect the reproduction and regeneration of grassland. With the increase of grassland age, the underground biomass showed ascendant trend, but fencing grassland was a much smaller increase than grazing. Underground biomass distributed mainly in 0～10cm soil layer, and was significant higher than other two layers. The distribution of underground biomass in the 0-30cm in soil is show pour pyramid, 0-10cm, 10-20cm, 20-30cm, the biomass is decline in turn.In the first year of fencing both the total cover and the cover of dominant species was higher than before the fencing. In the second year of fencing it decline obviously, it no significant differences with grazing grassland. The cover of standing dead litter in the first year and the second year of fencing were respectively 9.4%, 31%. With the increase of grassland age, the height of reproductive branch and vegetative branch of Elymus nutans showed decline trend, and it on fencing grassland was litter than grazing. The height of grassland community has the same trend because of dominant species influence. In the second year of fencing, the density and the biomass of reproductive branch and vegetative branch of Elymus nutans were lower than grazing obviously, and the reduce extent of reproductive branch more than vegetative branch.The content of soil organic carbon, total nitrogen, available nitrogen, total phosphorus, available phosphorus decreased generally with the depth of soil in various kinds of plots, but PH value was opposite trend. After fencing the content of soil organic carbon, total nitrogen, available nitrogen, total phosphorus, available phosphorus on fencing grassland was lower than before fencing. But the content of every layer has different change. The content of PH value, total nitrogen, available nitrogen in every layer in 0-30cm and available phosphorus in 10-20cm,20-30cm have same change trend, namely it was dropped in the first year of fencing then rebounded. From the total content in 0-30cm, total nitrogen, available nitrogen, total phosphorus, available phosphorus, PH value have showed"high-low-high"or"v"trend. In the grazing grassland, the content of available nitrogen, total phosphorus, available phosphorus, PH value has this"v"change trend.After fencing, crude protein content increased gradually, the content of grazing also increases gradually, the content of crude ash, crude fiber, total phosphorus content in three years has "V" change trend, the content of crude fat, nitrogen-free has a pour "V" change, the content of crude protein, total phosphorus and nitrogen-free in fencing grassland was lower than grazing, crude ash, crude fat content in fencing grassland higher than grazing, crude fiber content in the first year of fencing was lower than grazing, but it in the second year of fencing was higher than grazing.Fencing has no advantage in normal growth and development of forage, and it will keep down the plant regeneration and the formation of seedlings, and disadvantage with reproduction and regeneration of grassland. So as to the"back soil beach"sowing grassland that has higher productivity at the Yangtze and yellow River regions, it should be proper use, it can stimulate forage tiller and promote forage so that grassland ecosystem of the energy flow and material circulation keep the benign condition, and maintain keep grassland ecosystem balance.