Analysis on the Grain Supply in the Region with Soil Erosion on the Loess Plateau in the Future
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The region with soil erosion in the Loess Plateau is located in the upper-middle reaches of the Yellow River, its total area is 2.77× 105 km2, it is one of the regions with the most considerable contradictions between the population, resources and environment in China, and is also one of the regions with the most serious soil erosion in the world. According to the data, the area with soil erosion in the region is as large as 2. 32×10 km2, it occupies 81. 8% of the total land area. Agriculture, especially grain production has an important position in the region, and it is of vital importance for the social stability and the economic development in the Loess Plateau to achieve the stable increase of grain yield. However, the shortage of grain supply in the Loess Plateau will become more serious along with the population growth, urbanization, implementation of the project of withdrawing from farming to afforesting and grass planting. In this paper, the soil erosion and its causes in the Loess Plateau are analyzed. It is considered that it is an effective measure for controlling soil erosion to implement the project of withdrawing from farming to afforesting and grass planting. By analyzing the factors affecting the grain supply in the Loess Plateau, the grain supply in the region with soil erosion in next 30 years is discussed. It is suggested to develop grain production so as to achieve the balance between the grain production and supply.Keywords:
Loess plateau
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The Loess Plateau is one of the regions where the soil erosion is the severest and the eco-environment is the most fragile. The key factors, which influence on the environmental changes of the Loess Plateau, are soil erosion, soil and water conservation, bearing capacity of water resources and vegetation rehabilitation. The vegetation repairing and rehabilitation is the key for the ecological construction in the area. An unprecedented achievement of soil and water conservation in the Loess Plateau has been obtained since 1949, but the efficiency of the forest and grassy vegetations for soil and water conservation in the whole engineering of eco-environmental construction in the area is very low, for example, the amount of blocking sands of the vegetations accounted only 0.2% for the amount of blocking sands of the whole engineering, the comprehensive benefit of the vegetations can't completely be brought into play. The paper discussed the problems related to the vegetation repairing and rehabilitation for soil and water conservation in the Loess Plateau, in order to quicken the speed and to better the quality of the eco-environmental construction engineering. The problems mainly discussed as follow: A. Selecting community types: the zonal vegetations of the Loess Plateau are confirmed by precipitation, temperature and aridity, and non-zonal vegetations are decided by the micro habitats forming from landform, relief, soil, slope position, slope degree, exposure and so on. B. Selecting varieties or species of trees and grasses: keeping to the principle which trees or grasses are planted by their suitable sites, the dominant and constructive species are selected as afforesting trees and planting grasses in the area according to the distribution of the zonal and non-zonal vegetations and vegetation community composition. C. Determining the densities of vegetations: the optimum vertical configuring patterns of arbors, shrubs and grasses are determined according to the vegetation biological and ecological characteristics, physiological consumption and ecological requirement water, and the eco-environmental construction objectives, so are the optimum densities at the beginning of planting and the dynamic management of the densities. D. Forest or vegetation coverage: the optimal forest or vegetation coverage in the Loess Plateau is determined in the light of the eco-environmental construction objectives, regional economic development level, climatic fluctuations, environmental bearing capacity, especially bearing capacity of water resources. E. Response of water resources to implementing the measures of soil and water conservation: the influences of water resources in the region and whole Yellow River from the different eco-environmental construction objectives for soil and water conservation at different stages in the future.
Loess plateau
Landform
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Through analysis of agriculture water resources and regularity of aridity on the loess Plateau, the authors thinks: the key period of water requirement of the main crops is just the period of lower soil moisture; the peak period of rainfall synchronize with evaporvation; the soil evaporation changes greatly; the soil efficiency is lower in storing water; deficiency of soil moisture is frequent; and the water requirement is different for different crop and different region. By a great deal of investigation this paper gives the strategy of efficient utilization of water resources in the region.
Loess plateau
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The soil erosion of lower hilly red soil regions in Zhejiang was studied in this paper. There are two main models, a FCD model which can decrease the interferences from shadows, and a mixed pixel model to estimate vegetation coverage. According to the Standards for classification and gradation of soil erosion, the intensity of soil erosion was obtained from vegetation coverage, slope, land-use and other factors. Results show that vegetation coverage is in a good status that the vegetation fraction is generally more than 30%, and the soil erosion in the study area is slight, but agricultural land such as plantation is rather serious, especially the area where intense erosion plantation has reached 17.65%. In addition, tillage is another very important factor in engendering soil erosion, which should be paid more attention in calculating soil erosion. However, soil erosion is likely to occur in such areas, so the preventing and controlling of soil erosion still needs more attention.
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Using the PI model this paper simulates the changing trend of the land productivity under the natural process,soil conservation and fertilization on the sloping lands in the southern Loess Plateau.The results show as follows: the decline speed of the sloping land productivity under the nature process is very quick,the productivity annually reduces averagely by 0.25% to 0.5%;the decline speed under the soil conservation decreases by 0.07%(level terrace),0.15%(sloping terrace) and 0.21%(contour plant),compared with the nature erosion;the land productivity get obvious instauration as the measures of soil conservation and fertilizer are applied;The soil conservation measure can decrease the decline speed of the land productivity,but can't effectually recover the productivity;only application of the soil conservation measure along with fertilization can retrieve and enhance the land productivity.
Terrace (agriculture)
Loess plateau
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Land degradation is an important factor restricting social and economic sustainable development in the Loess Plateau,China.In this study,a field survey was carried out to investigate the soil nutrients under different land use types(woodland,grassland,orchard,terrace and slope farmland) in the plateau.The analyzed results of 8 soil nutrient indicators at 33 sample sites showed that the effects or impacts of different land use types on soil erosion were quite different,especially for the indicators,such as soil organic matter content,total nitrogen content and available nitrogen content.The soil organic matter content and total nitrogen content were in an obvious order of woodland slope farmland ≈ terrace orchard grassland,the available P content was in an order of orchard slope farmland terrace woodland grassland,and the available P content under crops was obviously higher than that under natural vegetation.The study results revealed that terrace,as a traditional soil conservation practice,could perform very well in conserving soil nutrients,but the soil conservation capability of slope grassland was the poorest in the gully-hilly region of the Loess Plateau.
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Loess plateau
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The transport of eroded soil to rivers changes the nutrient cycles of river ecosystems and has significant impacts on the regional eco-environment and human health. The Loess Plateau, a leading vegetation restoration region in China and the world, has experienced severe soil erosion and nutrient loss, however, the extent to which vegetation restoration prevents soil erosion export (to rivers) and it caused nutrient loss is unknown. To evaluate the effects of the first stage of the Grain for Green Project (GFGP) on the Loess Plateau (started in 1999 and ended in 2013), we analyzed the vegetation change trends and quantified the effects of GFGP on soil erosion export (to rivers) and it caused nutrient loss by considering soil erosion processes. The results were as follows: (1) in the first half of study period (from 1982 to 1998), the vegetation cover changed little, but after the implementation of the first stage of the GFGP (from 1999 to 2013), the vegetation cover of 75.0% of the study area showed a significant increase; (2) The proportion of eroded areas decreased from 41.8 to 26.7% as a result of the GFGP, and the erosion intensity lessened in most regions; the implementation significantly reduce the soil nutrient loss; (3) at the county level, soil erosion export could be avoided significantly by the increasing of vegetation greenness in the study area ( R = −0.49). These results illustrate the relationships among changes in vegetation cover, soil erosion and nutrient export, which could provide a reference for local government for making ecology-relative policies.
Loess plateau
Vegetation Cover
Soil nutrients
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The Loess Plateau of China has the highest soil erosion rate in the world where billion tons of soil is annually washed into Yellow River. In recent decades this region has experienced significant climate change and policy-driven land conversion. However, it has not yet been well investigated how these changes in climate and land use have affected soil organic carbon (SOC) storage on the Loess Plateau. By using the Dynamic Land Ecosystem Model (DLEM), we quantified the effects of climate and land use on SOC storage on the Loess Plateau in the context of multiple environmental factors during the period of 1961–2005. Our results show that SOC storage increased by 0.27 Pg C on the Loess Plateau as a result of multiple environmental factors during the study period. About 55% (0.14 Pg C) of the SOC increase was caused by land conversion from cropland to grassland/forest owing to the government efforts to reduce soil erosion and improve the ecological conditions in the region. Historical climate change reduced SOC by 0.05 Pg C (approximately 19% of the total change) primarily due to a significant climate warming and a slight reduction in precipitation. Our results imply that the implementation of "Grain for Green" policy may effectively enhance regional soil carbon storage and hence starve off further soil erosion on the Loess Plateau.
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Terrestrial ecosystem
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Dryland salinity
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