Effect Of Biochar And Reduced Fertilizer On Soil Physichemical Properties And Nutrient Utilization In Continuous Cropping

A field experiment was conducted to study the effects of biochar combined with reduced fertilizer on continuous cropping obstacles,causing the problems of poor growth and yield reduction of cucumber.The soil physicochemical properties,crop biomass,and fertilizer utilization rate were determined in this study.The objective of this work was to increase the yield and efficiency by improving continuous cropping obstacle soils and increasing fertilizer utilization rate.The results are significance for ensuring food security and agricultural sustainable development.In this study,the greenhouse of Rugao Agricultural Research Institute was selected as the experimental base.Biochar was applied to the soil at one time before the first season of cucumber cultivation.Six biochar application rates(0,5,10,20,30,and 40 t ha-1)were labeled as control(CK),C1,C2,C3,C4 and C5,respectively.After the continuous cropping conditions were formed,three fertilization levels(conventional fertilization,10%reduction,20%reduction)were carried out,The effects of biochar and reduced fertilizer on soil physicochemical properties,fertility,crop nutrient uptake and yield of continuous cropping were studied after the fifth,sixth and seventh seasons.The mechanism of continuous cropping obstacles and the improvement effects of biochar and reduced fertilization on continuous cropping obstacles were discussed.The differences of soil quality between different treatments were revealed principal component analysis.The clustering analysis was used to select the best allocation method for crop yield and nutrient utilization,and the stepwise regression analysis was used to screen the most significant factors affecting cucumber yield.The optimization measures were proposed based on the above research.The results will provide scientific basis for promoting the application of biochar,improving soil properties,increasing crop yield,reducing the amount of fertilizer applied,and green agricultural development.The main results were as follows:(1)Biochar can reduce soil bulk density aof continuous crops increased,the effectiveness of biochar showed a downward trend.Compared with conventional fertilization,the reduced fertilizer treatments reduced the soil bulk density and increased the soil porosity,the optimal biochar addition was 20%reduction.Compared with single fertilizer treatments,biochar and reduced fertilizer treatments can ameliorate the bulk density and porosity of continuous cropping.MWD and GMD of soil aggregates gradually decreased with the increase of continuous cropping times,but biochar could slow down the decline trend.The performance of MWD and GMD values in each treatment increased in order CK<C1<C2<C3<C4<C5.The result indicated that the addition of biochar can increase the stability of aggregates.Reducing the amount of fertilizer increased both MWD and GMD,with the highest at 20%reduction.The field capacity,available water content and saturated hydraulic conductivity showed an increasing trend with the increase of biochar,and reached maximum values with biochar addition at 40 t/hm2,with the increase trend is more obvious with the reduction fertilizer application treatments.Compared with CK under normal fertilization in the same season,the effectiveness of biochar addition reached the peak when the adding biochar was 40 t/hm2 and losing weight by 20%,among them,the field capacity in the fifth season increased by 23.28%,the available water content increased by 25.75%,and the saturated hydraulic conductivity increased by 100.72%.(2)Biochar can increase nitrogen content in soil,the soil total nitrogen content,ammonium nitrogen content and nitrate nitrogen content reached the highest values when the biochar addition was 40 t/hm2.Through reduced fertilization,the total nitrogen content,ammonium nitrogen,and nitrate nitrogen content in the soil were reduced to varying degrees,the lowest values were observed in 20%reduction treatment.With the increase of the amount of added biochar,the available phosphorus content in the soil showed an increasing trend,and reached the maximum when the amount of biochar was 40 t/hm2 in the fifth,sixth and seventh seasons.Continuous cropping will lead to the accumulation of available phosphorus in the soil.Reducing the amount of fertilizer applied can slow down the accumulation of available phosphorus in the soil.The lowest values were observed in 20%reduction treatment.The available potassium content in cucumber continuous cropping soil increased with the increasing of biochar,and reached the highest when the biochar addition rate was 40 t/hm2.After reduced fertilizer application,the content of available potassium in continuous cropping soil decreased,continuous cropping would cause soil acidification and decrease pH,adding biochar could neutralize soil acidity and increase soil pH.With the increase of biochar,the soil pH showed an upward trend,and reached the highest value with C5 treatment.Reduced fertilization could also slow down soil acidification,with the best effect at a 20%reduction.The electrical conductivity in the soil increased gradually with the number of continuous croppings,and the addition of biochar could reduce the electrical conductivity of the soil.When the biochar addition is 40 t/hm2,the electrical conductivity reached lowest level.Excessive application of chemical fertilizers will also lead to an increase in electrical conductivity,which could be reduced by reducing fertilization,when losing weight by 20%,the decrease in electrical conductivity reached 22.22%,20.80%,and 20.13%.(3)With the increase of biochar addition,the cucumber yields of continuous cropping showed an upward trend in the fifth,sixth and seventh seasons.When the amount of biochar was 40 t/hm2,the cucumber yield was the highest.After biochar addition,the yield of continuous cropping cucumber did not decrease significantly under the conditions of 10%and 20%reduction of chemical fertilizer application,especially when the amount of biochar was more than 20t/hm2.The cucumber yield increased with chemical fertilizer reduced application.The biochar could increase the above-ground biomass of continuous cropping cucumbers,and the highest value of above-ground biomass was observed when the biochar addition was 40 t/hm2.The single plant can reach 52.09 g.When the amount of biochar reached 10 t/hm2 and above,a 10-20%reduction in fertilizer application will not affect the above-ground biomass of cucumber.(4)The addition of biochar can improve the absorption and utilization of nitrogen,phosphorus,and potassium in the fifth-season continuous cropping cucumber.The maximum values were observed when the biochar addition reached at 40 t/hm2.Under conventional fertilizer conditions,compared with CK treatment,the increase rates of nitrogen,phosphorus,and potassium fertilizers added with biochar treatment were 80.33-337.44%,92.08-177.94%,22.01-120.69%.Under the treatment of reduced fertilization,the utilization rate of nitrogen,phosphorus,and potassium showed a gradual increase trend.When the fertilizer was reduced by 20%,the nitrogen,phosphorus,and potassium utilization reached the highest.The combined effects of reduced fertilizer and the addition of biochar significantly increased the utilization of nitrogen,phosphorus,and potassium fertilizers.When the C5 treated fertilizer was reduced by 20%,the nitrogen,phosphorus,and potassium utilization rates reached 31.08%,7.63%,and 45.46%.Adding biochar and reducing fertilizer could improve the agronomic efficiency of nitrogen,phosphorus,and potassium fertilizer in the fifth season of continuous cropping of cucumber.As the amount of biochar increasing,the agronomic efficiency tends to increase and reached the maximum value of 154.96 kg/kg at 20%reduction.The apparent recovery of nitrogen,phosphorus,and potassium in the fifth season of cucumber continuous cropping increased in order CK<C1<C2<C3<C4<C5,indicating that the addition of biochar could increase the apparent recovery of nitrogen,phosphorus,and potassium fertilizers under continuous cropping.Reduced fertilization treatment could also increase the apparent recovery of NPK fertilizers,reaching the maximum value at 20%reduced fertilization.(5)The results of principal component analysis showed that the comprehensive score of the fifth season of continuous cropping cucumber soil under the condition of different biochar content increased in order CK<C1<C2<C3<C4<C5,this indicated that biochar had a significant improvement on continuous cropping soil,and the higher the amount of biochar,the more significant the effect,when the biochar was added at 40 t/hm2,the comprehensive soil score reached the peak value.(6)From the cluster analysis,the results showed that the addition of biochar and reduced fertilization had different effects on the yield and fertilizer utilization on the fifth continuous cropping cucumber.In the combined treatment of biochar and reduced fertilization,the yield of cucumber and fertilizer utilization rate reached the highest values with the third type treatments(biochar 40 t/hm2 fertilizer 0.9 t/hm2,biochar 30 t/hm2 fertilizer 0.8 t/hm2,and biochar 40 t/hm2)chemical fertilizer(0.8 t/hm2),in the fifth season of continuous cropping.(7)Through stepwise regression analysis of independent variable factors such as soil physical and chemical properties and cucumber yield factors,the most significant influencing factors for cucumber yield were selected:nitrate nitrogen and available potassium,and the regression equation(mathematical model)was:y=23.839 x10+22.777x12-332.403,so the yield of continuous cropping cucumber can be increased by increasing the ratio of nitrogen and potassium fertilizers.