The Effect Of Amygdalus Pedunculata Pall. Plantation On Soil Quality In Newly-Built Terraces

Converting sloping land into terraces is one of the main measures to prevent soil erosion in the Loess Plateau region,but the construction of terraces destroys the soil structure and adversely affects the soil hydraulics properties and soil nutrients,resulting in low productivity of the newly-built terraces.Vegetation construction is one of the effective ways to make effective use of newly-built terraces and to improve soil quality.Exploring the changes in the physical and chemical properties of newly-built terraces under vegetation construction is conducive to exploring new methods for the construction of high-standard terraces.In this study,taking the newly-built terraces planted with Amygdalus pedunculata Pall for 5 years as the research object,the newly-built terraces without vegetation restoration（bare land）as the control,the nearby long-term natural grassland and the Caragana Korshinskii land with a planting period of 8 years were taken as the comparison,the effects of Amygdalus pedunculata Pall planting on soil structure（soil aggregation,bulk density）,hydraulic properties（saturated hydraulic conductivity,water characteristic curve）,nutrients（organic matter,total nitrogen）,and water consumption（water deficit degree）were evaluated over a field experiment combined with laboratory analysis.The minimum data set was established by using principal component analysis,and the soil quality index was calculated by combining the affiliation function.The main results showed that:（1）planting Amygdalus pedunculata Pall significantly improved the soil structure of the newly-built terraces.The water-stable aggregations of 0.25–2 mm in the 0–10 cm soil layer of the newly-built terraces with Amygdalus pedunculata Pall were significantly increased by 85%compared with the bare land,and reached 13%and 14%of those of natural grassland and Caragana Korshinskii land,respectively.The mean weight diameter and geometric mean diameter of the soil and the stability of aggregation of the newly-built terraces with Amygdalus pedunculata Pall were increased by 95%,65%and 63%compared with the bare land,and reached 61%and 66%,53%and 58%,68%and 71%of those of natural grassland and Caragana Korshinskii land,respectively.（2）Planting Amygdalus pedunculata Pall could improve the water-holding capacity of the newly-built terraces.The saturated hydraulic conductivity of the soil in the 0–10 cm soil layer was varied significantly between treatments,in the following order:bare land(0.36 mm min^-1)>Caragana Korshinskii land(0.19 mm min^-1)>natural grassland(0.15 mm min^-1)>Amygdalus pedunculata Pall land(0.12 mm min^-1).The water characteristics curve shows that the volumetric water content of Amygdalus pedunculata Pall land was higher than that of bare land for the same water suction,indicating that the water holding capacity of the newly-built terraces was improved by planting Amygdalus pedunculata Pall.The volumetric water content of the soil under different water absorption was fitted by the van-Genuchten（v-G）model（R²>0.98）.The retained water content（θ_r）in the 0–40 cm soil layer of Amygdalus pedunculata Pall land was higher than that in bare land.The saturated water content（θ_s）in the 0–40 cm soil layer was higher in the following order:natural grassland>Caragana Korshinskii land>Amygdalus pedunculata Pall land>bare land.（3）Soil moisture was deficited by Amygdalus pedunculata Pall in the 1–6 m.The total soil water storage in the 1–6 m soil layer of Amygdalus pedunculata Pall land（531.53 mm）was significantly lower by 46%compared to the bare land（986.28 mm）,while it was not significantly different from that of the Caragana Korshinskii land（517.17 mm）.The degree of soil water deficit in Amygdalus pedunculata Pall land in the 1–6 m soil layer was 43%,56%,58%,43%and 25%respectively,with non-significant differences between the degree of water deficit in Amygdalus pedunculata Pall land and Caragana Korshinskii land.（4）Planting Amygdalus pedunculata Pall could increase soil nutrient content,improve soil fertility and effectively improve the soil.The organic matter content of the surface layer of Amygdalus pedunculata Pall land(8.98 g kg^-1)was significantly increased by 84%compared with the bare land(4.88 g kg^-1),and reached 31%and 58%of those of natural grassland(28.94 g kg^-1)and Caragana Korshinskii land(15.46 g kg^-1),respectively.The total nitrogen content of Amygdalus pedunculata Pall land(0.55 g kg^-1)was significantly increased by 79%compared with bare land(0.31 g kg^-1),and reached 36.04%and 47%of those of natural grassland(1.53 g kg^-1)and Caragana Korshinskii land(1.16 g kg^-1),respectively.The total phosphorus content of Amygdalus pedunculata Pall land(0.62 g kg^-1)was significantly increased by 8%compared with bare land(0.57 g kg^-1),and exceeded 16%and 17%of those of natural grassland(0.53 g kg^-1)and Caragana Korshinskii land(0.53 g kg^-1),respectively.（5）Planting Amygdalus pedunculata Pall could significantly improve the quality of newly-built terraces.The minimum data set was established by using principal component analysis,and the soil quality index was calculated by combining the affiliation function.In the0–20 cm soil layer,the soil quality index was in the following order:natural grassland（0.80）>Caragana Korshinskii land（0.70）>Amygdalus pedunculata Pall land（0.38）>bare land（0.24）.In the 20–40 cm soil layer,the soil quality index was in the following order:natural grassland（0.72）>Caragana Korshinskii land（0.67）>Amygdalus pedunculata Pall land（0.56）>bare land（0.19）.This study proved that the planting Amygdalus pedunculata Pall could improve the soil structure and nutrient content and effectively improve the soil quality of the newly-built terraces.Therefore,it could be introduced into the soil improvement process of newly-built terraces in the mountainous area of southern Ningxia for the use of newly-built terraces and soil improvement.This study provides technical measures and theoretical basis for the improvement and use of newly-built terraces.