| The southern grassy hills and slopes distribution area has a humid climate,suitable temperature and suitable for forage growth,which has high production and ecological value.Different land use methods will affect soil fertility,plus there are environmental problems such as soil erosion,soil acidification and surface pollution in the southern land,which need to be solved urgently.Therefore,it is important to investigate the characteristics of soil and nutrient loss in southern grassy hills and grassy slopes under different land use methods for the rational development of soil and water conservation in southern grassy hills and grassy slopes.In this study,a representative natural grassy hill-grass slope,artificial grassland and farmland were selected in Huoyaping area of Changyang County,Hubei Province,with slopes of 30° and west orientation.A natural runoff field of 30 m in length,2 m in width and 0.5 m in depth was set up,and soil samples were collected from three land use types at 0-10,10-20 and 20-30 cm depths to determine their soil physical and chemical properties.One-way ANOVA and multiple comparisons were used to investigate the differences in nutrients between land use patterns and different soil layers,and the soil quality levels of each land use type were evaluated using principal component analysis.The effects of environmental factors and land use practices on runoff volume and its nutrient concentrations of nitrogen and phosphorus in runoff,as well as the differences in runoff nitrogen and phosphorus nutrients between different land use practices were analyzed by correlation.It aims to provide effective data support for rational land development and utilization and soil and water conservation in the south.The main conclusions of the paper are as follows:(1)Effects of land use patterns on soil fertility: The total nitrogen,total carbon,organic carbon,effective phosphorus and p H of the three land soils characterized 39.8% of soil fertility,and the microbial population characterized 30.8% of soil fertility.In a comprehensive comparison,the soil fertility level was natural grass hills and slopes > artificial grassland >farmland.It indicates that the overuse of farmland leads to the decrease of soil fertility level,and the establishment of artificial grassland plays a good role in soil fertility maintenance.(2)Characteristics of flow and sediment production under different land use methods:The flow and sediment production of all three land use methods increased with the increase of rainfall intensity level.The surface runoff and sediment loss of farmland were significantly higher than those of artificial grassland and natural grassy hills and slopes(P< 0.05),and the average yield of surface runoff was ranked from largest to smallest as farmland(8277 ml)>natural grassy hills and slopes(2204 ml)> artificial grassland(1071 ml).The average yield of subsurface runoff was ranked as natural grassy hill-grass slope(1436 ml)> artificial grassland(1054 ml)> farmland(651 ml),and the average sediment loss was ranked from largest to smallest as farmland(1845 g)> artificial grassland(434.39 g)> natural grassy hill-grass slope(237.6 g).It indicates that rainfall intensity is the key factor affecting soil erosion of the three types of land,the overuse of farmland increases the risk of soil erosion,and the establishment of artificial grassland has a good effect on preventing soil erosion.(3)Characteristics of nitrogen and phosphorus loss under different land use: N loss in surface runoff from farmland was significantly higher than that from artificial grassland and natural grassy hills and slopes(P< 0.05),with a maximum of 230 mg,and the main loss form was water-soluble N.There was no significant difference(P>0.05)between the N losses in surface and subsurface runoff from artificial grassland and natural grassy hillside slopes,which were mainly water-soluble N and nitrate N;the losses ranged from 10 mg to 20 mg.The contents of total N,nitrate-N and water-soluble N in subsurface runoff ranged from large to small: natural grassy hills and slopes > artificial grassland > farmland,and the contents of particulate N ranged from high to low: farmland > natural grassy hills and slopes > artificial grassland.The four forms of phosphorus in subsurface runoff from the three land use practices were not significantly different among the three lands(P>0.05).Therefore,scientific fertilization management measures should be taken to reduce the loss of nitrogen and phosphorus under different land use patterns,so as to protect soil and water resources.(4)To explore the main factors affecting nitrogen and phosphorus loss: Integrated analysis of soil science,ecology and biology shows that factors such as soil structure,vegetation cover,soil biological activity and climatic conditions have important effects on the production and loss of surface runoff and subsurface runoff.According to the correlation coefficient matrix,the loss of nitrogen and phosphorus in runoff was ranked in descending order of environmental influence: vegetation factor> climate factor > soil fertility.Therefore,the main factor affecting the loss of nitrogen and phosphorus in land runoff in the study area is the vegetation factor.Based on the above research,the effects of different land use patterns on ecosystem functions such as soil quality and runoff nutrients are significantly different.Long-term tillage of farmland will reduce soil fertility.Artificial grassland and natural grassland have high vegetation coverage,which can slow down the impact of rainfall,reduce runoff and prevent soil erosion.Therefore,in the southern region,appropriately changing farmland to grassland to increase vegetation coverage is helpful to improve soil and water conservation capacity,reduce soil erosion and non-point source pollution,and is of great significance to environmental protection and sustainable development.At the same time,reasonable management and control should be carried out according to different situations to maintain ecosystem health and stability. |
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