Effect Of Continuous Application Of Biochar On Soil And Water Conservation And Water Saving In Slope Farmland For Several Years

The black soil region in Northeast China is rich in soil fertility,good in soil properties,suitable for crop growth,which is the main grain producing areas of China.Most land of the black soil area in Heilongjiang province is hilly.With serious drought,the water storage of soil there is difficult.The season distribution of rainfall is uneven and concentrated.Accordingly,the problem of soil erosion in sloping farmland has being seriously threatened the regional ecological environment and national food security.In addition,Straw resources are rich in Heilongjiang province but low utilization rate.Putting them away with improper method would cause air pollution problem.As a new kind of soil improver,Biochar is of great significance in controlling the deterioration and improving the productivity of the black soil,diversifying and utilizing biomass resources efficiently.To discover the influences of the optimal amount and duration of biochar supply on water saving and yield increasing in slopping farmland of the region,the 3 years experiments were conducted based on runoff plot in 2015-2017 years.5 treatments were set according to different amount of biochar which were 0 t/hm~2,25 t/hm~2,50 t/hm~2,75 t/hm~2 and 100t/hm~2,and the same amount of biochar for each treatment was supplied continuously in 2016 and2017.A 10-seat runoff plot was set up(5 planting corn,5 planting soybean),in the bottom of which setting up automatic runoff and sediment recording system.Through the combination of sampling test inside and outside,the physical and chemical properties of each treated soil,rainfall runoff and soil erosion process,water distribution of soil layer,crop growth dynamics,yield and water use efficiency were observed.And then evaluate comprehensively the indicators.The test results show that:(1)The application of biochar can significantly reduce soil bulk density,increase total porosity,water holding capacity,and improve the composition of three-phase ratio of soil.The soil ph value,total organic carbon and effective nutrient contents were also improved.(2)The application of straw biochar can reduce the annual runoff of 3°arable land effectively.The biochar application amount of 50 t/hm~2 for two consecutive years got the best effect on the inhibition of surface runoff in soybean and corn test plot.According to the analysis of typical rainfall surface runoff process,it can be seen that the application of biochar could delay the start time and reduce the rate of runoff.However,when the rainfall intensity was high,the excessive amount of biochar would result in decreasing the effect of runoff inhibition and even increasing the runoff amount.(3)The effects of applicating straw biochar on soil erosion and erosion processed vary with the amount of applied.It is the best effect to reduce the total amount of soil erosion when the amount of 50 t/hm~2 was applied continuously for two years,while the amount of soil erosion would increase when the carbon was oversize.According to the observation of sediment process,the application of biochar could effectively inhibit the surface sediment production in low rain,and while the strong rain,the effect of biochar becoming weakened,causing that the amount of surface sediment was increased,and the content of biochar in the sediment increased.(4)The application of biochar can increase the amount of rainwater accumulated after a single rainfall and slow down the rate of its decline over time.(5)The application of Biochar influenced the distribution of soil moisture little in the depth0~100cm soil layer,but it effectively increased the soil moisture content in the depth of the0~60cm soil and no obvious influence showed on the deep soils.The optimum biochar content of soil in the 2015-2017-year tillage layer of soybean test plot respectively was 100,50 and 25 t/hm~2;The variation of soil water content in the corn test plot was similar to that of soybean plot,and the best performance in 2015-2017 years respectively in the soil was 100,50,50 t/hm~2 processing.(6)The variation of plant height,stem diemeter and LAI in each growth period of soybean and corn test are consistent.The trend of parabolic change was roughly with the increase of biochar.The 75 t/hm~2 treatment of biochar was the best in the soybean test plot in 2015,with the 50 t/hm~2treatment in 2016 and 2017.The high amount of biochar could lead to the decrease of the effect of soybean growth and even the inhibition.For the corn test plot,50 t/hm~2 treatment performanced best in 2015 and 2016,for 25 t/hm~2 treatment turning to 2017.The excessive amount of biochar can also cause the growth of corn to weaken,and even inhibit the development of corn plants.(7)Biochar can increase the yield of soybean and corn to different extent under different dosage.Increasing annual yield was the trend of first increase and then decrease with increasing biochar.Comparing with the three years’appearance,continuous application of biochar with the amount of 50 t/hm~2 was of the maximum yield in soybean test plot,increasing by 28.17%.It is superior to the one-time application of 100t/hm~2 biochar(the cumulative amount of the same)effect;The yield of corn was the highest when the 50 t/hm~2 was applied,and the increase reached14.12%.(8)According to three-year test results,the continuous application of biochar for two years with the amount of 50 t/hm~2 made the water use efficiency of soybean largest increase,to27.67%.And more than one-time application with the amount of 100 t/hm~2 effect ideal by 4.32%;One-time application with amount of 50 t/hm~2,of which the effect on improving water use efficiency of corn was the best,and its increase reached 17.57%,which was better than the application mode of biochar amount of 25 t/hm~2 for 2 consecutive years.(9)By using Grey Relation Projection,the comprehensive evaluations of soil improvement,soil and water conservation,water saving and yield increase,input-output of each biochar mode were obtained.By comparing the results of three-year trial evaluation,the best biochar application mode in soybean test plot was the application of biochar with the amount of 50 t/hm~2 for 2consecutive years.And the most feasible biochar application mode for corn was three years of continuous amount of 25 t/hm~2.