| The red soil hilly region of Southern Jiangxi is a serious area where soil erosion is serious in China.Soil texture is easily be eroded,the intensity of regional precipitation is large and the spatial and temporal distribution is uneven.Especially in the past 30 years,orchard development rate continued to rise,orchard area increased by 70% annually,which is the fastest changing land cover type.Because of attaching importance to development and belittling management,the soil and water conservation measures are not perfect.Because of weeds,ploughing and the use of herbicides,the undergrowth of the grass layer is missing,the vegetation coverage of the surface is low or even completely bare,and the problem of the forest downflow in the "far look at the green mountains in the near view of the water and soil flow" is outstanding.It is of great significance to study the mechanism of soil erosion in the red soil hilly area under the orchard development and evaluate the benefit of soil and water conservation under different engineering measures to solve the typical soil erosion problem in the red soil hilly region.In this paper,5 standard runoff plots(length and width 20m*5m,8 degrees)are established in the study area of the Ningdu County of Ganzhou,which are bare land,simulated natural arbor grass forest,Jo grass + horizontal bamboo grooves,mature orchard + ordinary terrace + ladder grass planting,young navel orange + trans terrace + staircase and ladder wall planting,by installing rainfall.The characteristics of runoff and sediment yield was analyzed in each runoff plot under different rainfall conditions,and the effect of sediment reduction and sediment reduction under different water conservation measures was compared,and the water conservation benefit under different measures was calculated and the best soil and water conservation was given.The main conclusions are as follows:(1)In the spring and summer of the study area,there are many precipitation events.There are more precipitation fields in Ningdu,but there are fewer runoff generation and precipitation fields.In terms of precipitation,40% of the precipitation accounts for 74.14% of the total precipitation.At the time of typical precipitation,the response time of the flow rate is the most appropriate and the response time of the flow rate of young navel orange is lagging behind in the bare land,and the maximum value of the rate of runoff generation is higher than that of the other three.The sand production time in the experimental plot lagged behind the beginning time of precipitation,and the lag time ranged from 2.5h to 9h.The sediment yield in the bare land,the simulated soil and water conservation forest and the young navel orange remained at a high level when the precipitation phase stopped,and the bare land was the most obvious.In the second stage of precipitation,the sediment yield is increased but not obvious.The sediment yield is still high after the end of the precipitation,and then the sand production ceases.(2)The interception effect of arbor stem flow directly affects the strength of forest downflow.There were 20 Chinese red pine in simulated soil and water conservation forest,and the maximum value of stem flow ratio was 14.5%.The tall trees and their larger canopy provide convenience for the formation of stemflow and reduce soil erosion.(3)The effect of precipitation at all levels above rainfall is 72.0%-100%.The effect of flow reduction in simulated natural forest is in 81.1%-100%.The effect of water reducing in simulated soil and water conservation forest is in 90.3%-100%.The effect of reducing flow in adult orange orchard + ordinary terrace is in 81.5%-100%.The effect of reducing flow of young navel orange orchard + trans-terrace is in 72.0%-100%.Under the condition of moderate rain and heavy rain,the reduction effect of all sites is between 83.6%-100%.The effect of flow reduction in simulated natural forest is in 87.9%-100%.The effect of water reducing in simulated soil and water conservation forest is in 84.9%-100%.The effect of reducing flow in adult orange orchard + ordinary terrace is in 83.6%-100%.The effect of reducing flow of young navel orange orchard + trans-terrace is in 83.8%-100%.In the field of sand reduction,32 fields of runoff producing precipitation in bare land have sand production.10 times in simulated natural forest,31.25% in sediment yield.14 times in simulated soil and water conservation forest,43.75% in the soil.11 times in adult orchards and 34.37% in a sediment yield.17 times in young navel orange orchard and 53.12% in sediment yield.Thus,the sediment yield in No.2-4 is small,indicating that the sediment yield of simulated natural forest,simulated soil and water conservation forest and mature orchard is less,and the effect of soil and water conservation is better,and the young orchard must rely on the early engineering measures to intercept the sediment.(4)In terms of soil and water conservation benefits,natural forests,soil and water conservation forests and adult oranges have a strong ability to reduce the flow of precipitation,which were approximately equal to the vegetation cover,the rational irrigation of grass,and the stratified interception of precipitation to reduce the kinetic energy of precipitation.Although the ability of young navel orange to reduce flow is weak,the effect of flow reduction is more than 72%,which indicates that the effect of the reverse terrace in the early stage of orchard development is more significant. |
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