Characteristics Of Soil Moisture And Abortion And Sediment Production In Artificial Young Forests Of Different Tree Species In Loess Hilly Region

Since the large-scale implementation of the“Returning Farmland to Forest（Grass）”project,the vegetation restoration in the loess hilly region has achieved remarkable results,and soil erosion has been effectively curbed.However,in the early stage of artificial afforestation,there are still differences in soil moisture,flow and sand production in artificial young forests of different tree species.Therefore,the rational selection of afforestation tree species and afforestation patterns to increase the soil and water conservation benefits of artificial young forests has become an urgent problem to be solved.In this study,the Zhifanggou watershed of Ansai District in the loess hilly and gully region was used as the experimental area,and six types of standard runoff plots were set up,including Robinia pseudoacacia,Pinus tabulaeformis,Platycladus orientalis,Forsythia（Forsythia suspensa）,clove（Syringaoblata Lindl）and Pine tabulaeformis*Forsythia mixed forest as the research objects,and the abandoned land as the control,the ECH₂O soil moisture monitoring system was used to monitor the soil moisture of different tree species from April to October 2021（20cm,50 cm,80 cm,120 cm,150 cm）,and collected secondary rainfall runoff,analyzed the soil moisture status of artificial young forests of different tree species,the characteristics of runoff and sand yield under secondary rainfall conditions,and the relationship between the two,in order to reveal the main factors affecting soil and water conservation benefits of artificial young forests,the research results are as follows:（1）The average soil water content of artificial young forests of different tree species over time is affected by rainfall.According to the change law of soil moisture,the experimental period can be divided into soil moisture dissipation period and soil moisture replenishment period.The average soil water content of artificial young forests of different tree species is as follows:mixed forest（20.8%）>Pinus tabulaeformis（18.6%）>Forsythia（16.6%）>Lilac（15.9%）>Arborvitae（13.3%）>Abandoned land（13.1%）>Robinia pseudoacacia（11.4%）.（2）Continuous sunny days will cause the soil desiccation degree on the surface（20 cm）of the artificial young forest to be more serious.The desiccation index was:Forsythia（58.7%）>Mixed forest（58.2%）>Abandoned land（58.1%）>Clove（53.8%）>Robinia pseudoacacia（48.3%）>Arborvitae（44.1%）>Pinus tabulaeformis（23.7%）.Serious desiccation（desiccation index>50%）of Forsythia and lilac soils mainly occurred in the 0-80 cm soil layer,while severe soil desiccation of Robinia pseudoacacia and Arborvitae mainly occurred in the deep layer of 120-150 cm.（3）The peak yield of artificial young forests of different tree species is:Pinus tabulaeformis（1.41 m³）>Arborvitae（0.31 m³）>Lilac（0.28 m³）>Forsythia（0.24 m³）>Robinia pseudoacacia（0.21 m³）>Abandoned land（0.13 m³）>mixed forest（0.11 m³）;the peak sediment yield was:Pinus tabulaeformis（10.9 kg）>Clove（4.2 kg）>Arborvitae（1.9kg）>Robinia pseudoacacia（0.7 kg）>Forsythia（0.7 kg）>Mixed forest（0.2kg）>abandoned land（0.03kg）;the peak runoff sediment content is:Pinus tabulaeformis（29.6 kg/m³）>Cloves（14.9 kg/m³）>Acacia（9.9 kg/m³）>Arborvitae（8.8 kg/m³）>Forsythia（4.9 kg/m³）>Mixed（2.8 kg/m³）>Abandoned land（0.9 kg/m³）.（4）According to rainfall erosivity（R,MJ·mm/（hm²·h））,rainfall is divided into 4 types of rainfall,type 1（R<50）is long duration,light rainfall,and low rainfall intensity;type 2（50<R<100）is long duration,heavy rainfall,moderate rainfall intensity;Type 3（100<R<200）is short duration,small rainfall,and super heavy rainfall;Type 4（R>200）is super long duration,super heavy rainfall,and heavy rainfall.Under the conditions of 4 types of rainfall,the flow rate is:type 4>type 3>type 2>type 1;the sediment yield is:type 3>type 4>type 2>type1;the sediment concentration in runoff is:type 3>type 4>Type 2>Type 1.（5）Both the individual and interactive effects of tree species and rainfall have significant effects on soil moisture（P<0.01）,and the order of importance is:tree species alone（65.09%）>rainfall alone（28.78%）>tree species,rainfall interaction effect（4.04%）;rainfall alone had a significant effect on runoff and runoff sediment content（P<0.05）.Except for clove yield and rainfall,which did not show a significant relationship,the other tree species and abandoned estate flow were significantly or extremely significantly positively correlated with rainfall,I₃₀,I₆₀,rainfall kinetic energy,and rainfall erosivity（P<0.05 or P<0.01）;the sediment yield and runoff sediment content of different tree species were significantly or extremely significantly positively correlated with I₃₀ and average rainfall intensity（P<0.05 or P<0.01）.The leaf area index of the artificial young forest was significantly negatively correlated with the yield and sediment yield（P<0.05）,and was extremely significantly negatively correlated with the runoff sediment content（P<0.01）.There was a very significant positive correlation between them（P<0.01）.