| Black soil is a precious land resource and has the reputation of“treasure of soil”.It has the characteristics of high fertility,good structure,suitable for crop growth.But in the northeast black soil area,farmland was overused without proper attention to the maintenance of its fertility for years,facing the difficulties of natural fertility decline year by year,soil degradation,and soil erosion,but black soil forms slow.And,the area is abundant with straw resources,a large number of them are abandoned or burned,this situation urgently needs to be handled properly.As the product of straw mulching,biochar can also be used as soil amendment in agricultural soil.Because of the particularity of its own structure and the stability of its components,biochar can exist in soil for a long time,and the effect on soil and crops is a long-term and complex process.Currently,there are many studies related on the effects of biochar on soil physicochemical property,soil and water conservation,water saving and yield increasing,but most of them are under the condition of short-term or continuous application.In order to ascertain the sustained influence of the application of biochar on sloping farmland in black soil region of Northeast China,this research take field runoff plot of 1.5°and 3°,5°slope as the research object,the experimental base is located at the comprehensive experimental station of Heilongjiang Province Hydraulic Research Institute.In 2016,before the start of the experiment,biochar was applied with 75t/hm~2 at one time,and a control group is programmed to set no use of biochar on each slope.Count up to 6 plots,Biochar was not applied in subsequent years.The continual effects of biochar from 2016 to 2019 on soil improvement,fertilizer cultivation,crop growth,soil conservation and yield increase were analyzed through indoor and outdoor experiments,and the law of subsequent effects of single application of biochar on various indicators was clarified.At the same time,the random forest model was used to comprehensively evaluate the soil fertility and predict the reasonable duration of biochar's effect on fertility.The following main conclusions are as follow:(1)The analysis results of post-effect of biochar on soil structural indicators showed that:one-time application of biochar can effectively reduce soil bulk density,increase soil porosity,and reduce soil solid phase ratio,and increase the ratio of liquid and gas phase,decrease the R value of three-phase ratio within 4 years,the soil is closer to the ideal state,the soil structure is loose,the permeability is enhanced,and the saturation moisture content and field capacity are increased at the same time,and the water-holding capacity is improved,so that the growth environment is more conducive to the growth and development of crops.The effect of biochar on the above indicators weakened with time,and the effect of the increase in slope also showed a weakening trend.(2)The analysis results of the post-effect of biochar on soil fertility indicators showed:the soil organic matter content,ammonium nitrogen content,and available potassium content of the T treatment were significantly higher than that of the CK treatment within 4 years of biochar of a single application(P<0.05),and the level of soil nutrients were improved.At the same time,the p H is significantly increased to neutralize the acidity of the soil,so that the acid-base environment of the soil is more conducive to crop growth,and the comprehensive soil fertility is enhanced.The maximum increase rate of soil organic matter,ammonium nitrogen and available potassium content is 18.21%,27.23%,and 20.31%,respectively,the beneficial effects of biochar on each indicator decreases as the slope increases,and decreases with the application years.(3)The analysis results of post-effects of biochar on crop physiological indicators,yield and its component showed:a single application of biochar can increase soybean plant height,stem diameter,leaf area index and dry matter accumulation within 4 years.The difference between the T treatment and the CK treatment at the same growth period and the same slope ranged from a significant group of significant differences in 2016 to a significant group of less in 2019,indicating that the effect on crop height after one application showed a weakening trend,and at the same time,the application of biochar has a certain increase in stem thickness stem diameter,and leaf area index,but there is no obvious law.The distance between the T treatment and the CK treatment of soybean dry matter accumulation curve decreases year by year,indicating the effect of biochar application on the soybean dry matter accumulation weakened year by year.A single application of biochar can increase soybean yield,pod number per plant,grain number per plant,and the hundred grain weight within 4 years.The value of each index is negatively correlated with the slope,and the improvement rate of each index shows a decreasing trend year by year,indicating that the gain effect of biochar on yield and its components has been weakened year by year.(4)The analysis results of post-effect of biochar on soil and water conservation effect indicators showed that:a single application of biochar showed the reduction effects of runoff and sediment to a certain extent in the three-year rainfall-runoff test.During the natural rainfall process,in 2016,2017,2018 the three rainfalls,the runoff reduction rates of T treatment were 12.07%,9.88%,and5.92%,and the sediment reduction rates were 8.65%,6.76%,and 4.58%,respectively.It can be seen that the effects of biochar have reduced with years.In the process of artificial rainfall,in a total of9 rainfalls in 2016,2017,and 2018,with the increase of rain intensity,both runoff and sediment increased,and the trend in each year was the same.Under the same rain intensity conditions,the runoff coefficient increases year by year,and the runoff reduction rate and sediment reduction rate decrease year by year.It can be seen that under artificial rainfall conditions biochar can effectively reduce runoff and sediment,and the effect of runoff reduction and sediment reduction rate weaken continuously with the time.(5)A random forest regression model is used to evaluate the comprehensive fertility index and fit the regression equation to predict the index of 2020-2022.Comparing fertility changes,it is concluded that the reasonable and effective life for a single application of biochar on soil fertility is 6?7.Year. |
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