Study On The Effect Of Returning Farmland To Forestry(Grass) In Different Years

Since twenty-first Century,the government has fully implemented the project of "returning farmland to forest(grass)",which aims to bring the whole promotion of ecological quality to each area,and solve the problems of development.From 1999 to 2016,a number of policies have been put forward to constantly consummate the system of returning cultivated land to forest(grass).Through restoring vegetation and effecting the nutrient flow of soil and plant communities,it can make significant changes in the quality and quantity of soil carbon and nitrogen.It is an important measure to prevent soil degradation and land desertification,promote carbon fixation and prevent biodiversity loss.This study selected forestland after returning farmland to forest for 13,19 and 50 years in Xingtai,Hebei Province,and grassland after returning farmland to grass for 1,3,10 and 30 years,which compared with the surrounding farmland as the control.It will analyze whether the project of returning farmland to forest(grass)is effective and the possibility of it to be carried out,through analyzing the change of cover after returning farmland to forest(grass),the change of soil carbon and nitrogen content under different years of returning farmland to forest(grass),the change of planting income after returning farmland to forest(grass)and so on.The main conclusions are as follows:(1)After the conversion of farmland to forest(grass)project,the vegetation growth and development of the returned farmland and woodland and grassland were in good condition.Vegetation coverage and biomass increased with the increase in the number of farmland.The total coverage of forest land in 50 years was 39.08% and 6.99% higher than that in 13 and 19 years.The 30 year grassland biomass was 43.66%,22.11% and 2.36% higher than 1 years,3 years and 10 years respectively.Plant diversity index increased with the increase of years.This study shows that conversion of farmland to forest(grass)significantly improved the growth environment of vegetation,improved biodiversity and sustainability,promoting soil carbon and nitrogen accumulation.Vegetation growth enhances soil carbon sequestration capacity and increases soil carbon storage.(2)The soil organic carbon and total nitrogen increased significantly in the topsoil after returning to forest and grassland.The content of organic carbon and total nitrogen in all 0?20cm soil layers was greater than that of other soil layers.The content of the two was decreased with the depth of soil layer.After returning farmland to forest,the total organic carbon content in the surface layer was F19>CK>F50>F13 in turn.With the extension of the year of returning to forest and grassland,the total organic carbon content decreased first and then increased,then decreased.The content of organic carbon and total nitrogen in the surface soil of returning farmland to grass was G30>G3>CK>G10>G1,which showed a "serrated" growth trend.Conversion of farmland to forest(grass)can play a good role in regulating the C/N ratio of the whole soil profile.(3)After the conversion of farmland to forest and grassland,the total storage of soil organic carbon increased first and then decreased.The total soil organic carbon storage of the 19 year forestland and 10 year grassland in 19 years was increased by 69.45% and 53.02% than that in the uncultivated land,but the total organic carbon storage in the 50 year forestland and the 30 year grassland declined,but it was still 41.08% and 27.95% higher than that of the uncultivated land.The study shows that the soil environment,the soil quality,the carbon sequestration capacity of the soil and the organic carbon holding capacity of the soil have been greatly improved by the project of returning farmland to forest and grass.(4)Comparison of planting thin skinned walnuts with corn planted in converting farmland to forest.The resulting economic benefits will not decrease.With the increase of planting years,the net income of planting walnut is increasing,the ratio of output to investment is increasing rapidly,and planting income is increasing year by year.The planting income of walnut field in 13 years and 19 years was 47 616 yuan and 91 895 yuan respectively,which was 463.50% and 644.09% higher than that of corn field.Combined with the statistics of national subsidy policy,compared with planting corn,the total yield of walnut planting is even more substantial.The total income of walnut fields in 13 and 19 years was 49506 and 94645 yuan respectively,which was 485.87% and 666.36% higher than that of corn fields.(5)Therefore,after the conversion of farmland to forest(grass),the woodland grassland and the non reclaimed farmland were comprehensively compared,the vegetation type and quantity increased after returning farmland to forest(grass),which had positive effect on soil carbon and nitrogen accumulation.Farmers' planting income did not decrease,and the positive effect of returning farmland to forest(grass)was obvious.The project of returning farmland to forests(grass)should continue to be carried out in the fragile ecological areas.