A Study On The Sloping Farming Land Degradation Mechanism And The Protecting Measures Against Soil Erosion Degradation

A study with the runoff plot method,trace method of neutron activation of Eu fixed soil core,erosion stick method,system study method for soil nutrients and the protecting measures of tillage measures(contour planting),bio-measures(forest and grass covering),engineering measures(land terracing),integrated measures on the sloping farming land degradation mechanism and the protecting measures against soil erosion degradation was conducted on the typical sloping farming land of yellowish red soil in Bian Yang township,Luo Dian county of southern Guizhou province,aimed at the main factors for sloping farming land degradation,the existed problems in the research and lack of such studies.The key results in the dissertation were as follows:The sloping farming land degradation mainly resulted from soil erosion degradation,soil nutrient degradation and soil acidification.1.The key factors responded for soil erosion degradation was:1)High soil erodibility K value.Such as the K value of bare sloping farming land of yellowish red soil was 0.376 and the average K value of sloping farming land of yellowish red soil under different cropping systems and land utilizations reached 0.367.2)Poor soil anticrodibility with slightly change with the times.The average anticrodibility of sloping farming land of bare yellowish red soil was 69.49mm.3)Rainfall distribution asymmetry in a year and its strong erosivity.Rainfall in the sloping farming land area of yellowish red soil was rich.The average annual rainfall was 978.51mm.Most events of rainfall happened during April to August.The precipitation during this times accounted for 80.55%of total precipitation.The transformation ratio of rain to aggressive rain reached 75.96%,runoff ratio was higher to 80.37%.4)High rainfall erosivity R and its strong fatalness.The average rainfall erosivity R₁₀and R₃₀in the sloping farming land area of yellowish red soil were 474.57 and 351.94 respectively. It occurred a bit before rainfall when there was few plants growth on the land and the vegetation coverage was low so that it had much possibility to bring a danger of water loss and soil erosion.5)Lower vegetation coverage.The average monthly vegetation coverage in sloping farming land area of yellowish red soil was only 28.26%. The highest monthly vegetation coverage in a year was only 48.72%.6)Low biodiversity. There were only two kinds of plants on farmer's practice land in the sloping farming land area of yellowish red soil.There were only three to six kinds of plants on the land which under alley cropping systems,intercropping and contour cropping systems and terrace cropping systems,such kind of food production system.7)Low soil water storage.The average water contents of bare sloping farming land,farmer's practice land and the land under different cropping systems and land utilizations of yellowish red soil were only 16.61%,18.90%and 19.56%respectively.8)Deep slope.The land slope in testing area was 11.3-34.7°.The average degree of ground slope in Guizhou was 21.5°.The water loss and soil erosion increased with the increase of slope which was under 20°.9)Farming activities.Farming activities accelerated soil erosion obviously.The traditional farming caused serious soil erosion.2.Soil nutrient degradation caused by soil erosion which conduced to soil nutrient loss by quantity,by soil absorption which resulted in low efficiency of soil nutrient, by crop harvest which caused soil nutrient consumption.The nutrient degradation on sloping farming land of yellowish red soil was mainly because 1)Lots of soil nutrient was loss by water loss and soil erosion.The more serious water loss and soil erosion was the more soil nutrient loss.The soil nutrient loss reached 198.312-1536.121kg/ha.a cased by water loss and soil erosion on sloping farming land of yellowish red soil.2)Soil organic matter and total K loss were serious,reached 90.964-708.937kg/ha.a and 91.690-750.688kg/ha.a respectively through soil erosion.3)Soil available nutrient loss was serious, reached 6.245-21.467kg/ha.a caused by runoff.4)Available K and NO₃-N loss were serious,reached 3.642-14.842kg/ha.a and 1.772-7.108kg/ha.a respectively.5) Nutrient enrichment rate of sediment was high and nutrient concentration of runoff was high.The nutrient content in sediment was one time more than that in soil.There was a high P nutrient enrichment rate in sediment.Phosphorus content in sediment was 8 times higher than that in soil.The amount of available N and K washed away by runoff were 1.639-7.201 times and 2.079-17.577 times higher than that of sediment respectively.6)Soil absorption rates of P,K and B were high.The transformation rate of NH₄-N to NO₃-N was high and soil available nutrient concentration was low. The average soil absorption rates of P,K and B were 38.436%,26.915%and 30.236% respectively.The content of NH₄-N decreased sharply within 15d,the content of NO₃-N increased fast within 25d and then decreased from the 25d to the 35d after fertilization.7)Crop harvest was the main factor for soil nutrient loss.There was 127.296-1250.826kg/ha.a total soil nutrient loss by crop harvest on sloping farming land of yellowish red soil under different cropping systems and land utilizations, it accounted for 15.23-86.57%of total soil nutrient loss which was the sum of nutrient loss caused by water loss and soil erosion and crop harvest.The higher crop yield and biomass were the more soil nutrient loss.8)Plant species and their combination effected soil nutrient loss.To producing 1kg of soybean,daylily flower,chicory, rapeseed,purple medic,sweet potato vine,corn straw,corn and sweet potato needed 91.490g,78.567g,58.319g,54.077g,34.088g,29.120g,27.310g,22.009g and 14.953g of NPK respectively.Soybean,rapeseed and day lily needed more NP,and chicory,day lily and soybean required more K for their growth.Therefore,difference of plant kinds was the key factor for soil nutrient loss by bio-consumption.3.The mechanism of soil acidification on sloping farming land of yellowish red soil was:1)Low CEC and base-saturation percentage.Soil CEC was about 11 Cmol(+)/kg and base-saturation percentage was less than 30%in general speaking.They changed slowly in sloping farming land of yellowish red soil.2)Concentration of exchangeable Al⁺³was much higher than concentration of exchangeable H⁺.Concentration of exchangeable Al⁺³was high to 7.188 Cmol(+)/kg and concentration of exchangeable H⁺ was low to 0.688Cmoal(+)/kg in average.Exchangeable Al⁺³concentration was 10 times higher than exchangeable H⁺ concentration in general.3)Base-acid buffering ability of sloping farming land of yellowish red soil was low.Acid buffering ability was better than base buffering ability.Soil acid buffering capacity was arranged from 4 to 16 Cmol/kg and base buffering capacity was from 2.5 to 14.0 Cmol/kg calculated through the diagram.The regression coefficient b form parameters-of-fit of acid-base buffering ability curve was ranged -1.4981～-2.1297.Iron,CEC,NO₃-N and clay impacted on acid buffering ability and Mn,AA,OM,NO₃-N,pH,Mg impacted on base buffering ability.4.Erosion stick method was simple,easy to operate,saving time and labour.It could measure soil erosion roughly.The changes of soil erosion and aggradations could show up with erosion stick method.However,Accuracy of reading the erosion stick length above the land was affected by abnormal objects and phenomenon surrounding the erosion stick,fine scale of erosion stick and land slope etc.so that the result of soil erosion was affected.There was a problem for erosion stick method that how to change the soil erosion on a point to soil erosion on a slope land.Trace method of neutron activation of Eu fixed soil core could show up the soil erosion and aggradations on the small area of Eu fixed soil core.But this method could not measure runoff.It was a new method;the operating process needed to further regulate.Also,abnormal objects and phenomenon surrounding the core could affect the accuracy of soil erosion calculation.How to change the soil erosion on a point to soil erosion on a slope land was not easy to be solved by this method.Additionally,it needed precision tool and cost was high.Runoff plot method was more practical,flexible and accurate.It could determine soil erosion as well as runoff.It could be used for many fields of studies according to the purposes.Nevertheless,it was not good to be used for study on the spatial variances of soil erosion and aggradations.In addition,runoff plot was set up on the field;determination and observation were on the field,it consumed lots man power.5.Key technologies of sloping land degradation control were tillage measures, engineering measures,forest-grass measures and integrated measures.All had the function of soil,water and nutrient conservation,could increase vegetation coverage, soil root content and enhance biodiversity,and could raise the concentrations of OM,total N,total K,total P,available N,available K and slowly available K.But their effects on increasing crop yields and incomes,soil improvement and raising soil available P were various.Alley cropping measures had very good effect on crop yield and income increase.Zone-rotation cropping measures could raise soil pH,total P,total K,available P and slowly available K well.Intercropping measures could enhance soil anticrodibility,increase soil moisture and land surface coarseness well. Engineering measures had very good effects on soil,water and nutrient conservation, and reduced land slope;shortened slope length rapidly.Forest measures could enhance soil anticrodibility and biodiversity,increase vegetable coverage,OM and total N. Grass measures could increase soil root content,water stable infiltration rate and available N.Integrated measures had good effects on shortening slope length and reducing land slope.Compared the integrated effects of different measures on erosion degradation control of sloping farming land of yellowish red soil with that of farmer's practice,the best measures was integrated measures,the next was engineering measures,the next was forest-grass measures,and then the tillage measures.However,different tillage measures had different effects on erosion degradation control.Compared with them,alley cropping measures was the best measures for erosion degradation control.Intercropping measures was better for erosion degradation control than the zone-rotation cropping measures.6.Basically,the critical value of aggressive rainfall in sloping farming land area of yellowish red soil was 9.1mm.the most key climate factor of causing water loss and soil erosion was basically discovered that was rainfall erosivity R₁₀.The critical slope of soil erosion was basically found that were 20.00-24°and 17.10-20.00°for the sloping land under the traditional farming system and under the alley cropping system respectively.The concept soil erosion equation was basically worked out.It could be expressed as: A=b·R·K·C·P whereb of forest land,farmer's practice land,zone-rotation cropping land,terraced cropping with fruit trees land,engineering cropping land,intercropping land,alley cropping land,grass land and bare sloping land were 179,668,375,195,165,219, 214,202 and 147 respectively.K was 0.379。C of forest land,farmer's practice land,zone-rotation cropping land,terraced cropping with fruit trees land,engineering cropping land,intercropping land,alley cropping land and grass and were 0.851,0.219,0.385,0.724,0.853,0.681,0.697 and 0.728 respectively。P of forest land,zone-rotation cropping land,terraced cropping with fruit trees land,engineering cropping land,intercropping land,alley cropping land and grass and were 0.191,0.788,0.353,0.189,0.409,0.388 and 0.348 respectively。The erosion modulus of bare sloping farming land of yellowish red soil was 25.8-631.2t/ha.a which belonged to erosion intensityâ…¢-â…£graded by Water Conservation Ministry of People's Republic of China.That was serious and very serious soil erosion.Although different cropping systems and land utilizations could reduce soil erosion the lands under tillage cropping system which included farmer's practice,zone-rotation cropping,intercropping and alley cropping systems were still in danger of very serious erosion and the lands under terraced cropping with fruit and grass land were still in danger of erosion in recent years.Soil acidification was visible in sloping farming land area of yellowish red soil.The pH value was between 4.420-5.790.The variance of soil erodibility K calculated with formulaâ…¡was small. The variance of soil erodibility K came from nomograph was small too and it was easy to get from nomograph.So they are good methods for K value calculation in sloping farming land area of yellowish red soil.The better indexes for evaluating soil anticrodibility of sloping farming land of yellowish red soil were soil aggregation state,degree of soil aggregation and ratio of sand and sum of clay and fine sand because their results of soil anticrodibility evaluation were similar and the variances of their value were small.The method of parameters-of-fit of acid-base buffering ability curve was good to get soil acid-base buffering capacity.It is feasible that fuzzy mathematics was used for integrated effects evaluation of sloping farming land erosion degradation control under different measures.