Soil Quality And Crop Yield Were Affected By Different Black Soil Gully Erosion

Black soil areas are degraded by soil erosion and human activities,and surface runoff erosion leads to gully erosion development,which further affects soil quality and crop yield.However,current studies mainly focus on the influence of gully erosion on soil nutrients and crops,but do not comprehensively consider the influence of black soil gully erosion on nearby soil hydraulic properties and spatial heterogeneity of crop yield at different latitudes and slopes.Therefore,the purpose of this study is to reveal the effects of different erosion gullies on the soil hydraulic characteristics（soil field water capacity,wilting coefficient,available water,available water,delayed water,saturated water conductivity,bulk density,etc.）and the spatial distribution characteristics of soil nutrients（organic matter,NPK）at different positions and distances.The effects of soil quality（SQI）characteristics on crop yield at different distances near gully were revealed.The erosion gullies（1%,2%,3%）of different slopes in three typical black soil areas with different latitudes in Jiusan,Hailun and Harbin of Heihe City,Heilongjiang Province（9 gullies in total）were selected.The shape index of the gully was measured on site.Sampling points are set at gully side（PG₀）and 50m transverse side(PG₅₀)of the above 9 gullies.Sampling points include:main gully head,middle and upper gully,waist,middle and lower gully,gully mouth and other key gully side locations where main gully and branch gully meet,waist of branch gully and branch gully mouth.Soil samples and ring cutter samples were taken from the above sites and used for soil water characteristic curves,soil saturated water conductivity,structural indexes（soil porosity,bulk density）,organic carbon,total nitrogen,available P and available K that affect these hydraulic properties.At the same time,theoretical crop yields at PG₀ and PG₅₀ locations were measured.The following main results are obtained:（1）Soil hydraulics were affected by different erosion channels.Soil available water and available water at the gully edge（PG₀）were significantly lower than those at PG₅₀,and the available water at PG₀ was 6%～50%lower than that at PG₅₀.Soil available water and available water present the rule of Jiusan（0.16,0.11 cm³/cm³）>Hailun（0.12,0.07cm³/cm³）>Harbin（0.13,0.06 cm³/cm³）at different latitudes under the same slope.Taking 1%slope as an example,The distribution trend of soil available water was Jiusan（0.68）>Hailun（0.57）>Harbin（0.46）.The soil available water increased with the increase of slope in Harbin and Hailun,and decreased with the increase of slope in Jiushan.Comparingθ₃₀-θ₁₅₀₀ andθ₃₀-θ₃₃₀/θ₃₀-θ₁₅₀₀ ratios to healthy soils with similar clay content in other countries,θ₃₀-θ₁₅₀₀ was similar to other countries,but the black soil erosion of the gully edgeθ₃₀-θ₃₃₀/θ₃₀-θ₁₅₀₀（0.57）was lower than that of other countries（0.63）.The soil saturated water conductivity at PG₀ was significantly lower than that at PG₅₀,but there was no obvious rule between latitude and slope.In conclusion,the differences of soil available water,available water and saturated water conductivity at different distances from the ditch edge,latitude and slope are directly related to the differences of soil bulk density,which is relatively 0.5%～48%higher at PG₀ than at PG₅₀.（2）Soil nutrients（organic matter and NPK）showed spatial differences with the location difference of erosion gully.The soil organic matter content at the gully edge was decreased by erosion,and the difference of organic matter at the gully tail with a larger slope of 3%was the most obvious.The organic matter at PG₀ was 0.61%～68.61%lower than that at PG₅₀.The organic matter in the same slope at different latitudes showed the rule of Jiusan（45.52 g/kg）>Hailun（39.05 g/kg）>Harbin（31.98 g/kg）.The difference of organic matter between different slopes at the same latitude shows that the rule of 2%<3%<1%from the head of the gully to the tail of the gully at different positions is 2%<3%<1%（Harbin）,3%<2%<1%（Hailun）,and 1%<3%<2%（Jiusan gully from the waist to the tail of the gully）.The contents of total nitrogen,available phosphorus and available potassium were 5%～70%,4%～74%and 2%～70%lower in PG₀ than in PG₅₀.In the same slope,the total nitrogen content showed that Harbin（1533.80 mg/kg）<Hailun（1655.04 mg/kg）<Jiusan（1744.28 mg/kg）,and the total nitrogen content and available potassium content decreased with the increase of the slope（Harbin）.（3）Soil quality index（SQI）near erosion gully was determined by six soil indexes:soil void porosity,TN,silt,sand,clay and Ks.The SQI of PG₀ is 2%～48%lower than that of PG₅₀.The SQI of the gully tail increased with the increase of latitude（Jiusan>Hailun>Harbin）,but the other locations showed the opposite trend.The SQI-M values of different gradients in Harbin show a rule of 3%<2%<1%at the head and waist,and 1%<2%<3%at the tail.The SQI-M value of Hailun’s gully showed a rule of 1%<3%<2%.The SQI-M value of Jiusan showed a rule of 2%<3%<1%from the waist to the tail.The soil quality of gully edge（PG₀）affected by erosion gully decreased,resulting in crop yield at PG₀ was significantly lower than that at PG₅₀（0-30%）.The difference of crop yield between latitude and slope was not found.Mastering the influence range of erosion gully on the hydraulic properties and nutrients of nearby black soil is helpful to further understand the influence of affected soil properties on crop growth,and provide certain support for the precise management of future farmland zoning.