Effects Of Different Irrigation On Physical And Mechanical Properties Of Clay Soils In The Short Term At Different Biochar Application

Preparing biochar from agricultural waste straw and returning it to the field can effectively reduce the burning pollution,which increases the ability of the soil to retain water and fertilize.With the introduction of national 30 and 60 carbon emission policies,making biochar from waste straw for return to the field will be vigorously promoted.Therefore,understanding the changes in physical and mechanical properties of soil under different application of biochar and different irrigation amount can provide a theoretical reference basis for the formulation of irrigation systems and the design of agricultural implements for farmland after improvement by biochar,and is of great importance to promote sustainable agricultural development.To investigate the short-term effects of different irrigation amount on soil physical properties,mechanical properties,and crop growth under biochar application,this study used three levels of biochar application and irrigation amount.The biochar application rates were B0(0 t/ha),B1(25 t/ha),and B2(50 t/ha),with three irrigation amount of T0(1.2 Ep),T1(1.0 Ep),and T2(0.8 Ep),respectively.The physical and mechanical properties of soil were analysed by measuring indicators such as soil water characteristic curve,bulk density,aggregates,shear strength,and penetration resistance to reflect the changes in soil properties and provided data support for the design of agricultural tillage equipment.Considering the limitations of individual indicators,the individual physical and mechanical indexes of soil are combined into a comprehensive evaluation system,and the following conclusions are drawn through the principal component analysis:(1)The application of biochar can improve the water retention and the effect of biochar on soil water retention was greater under low substrate potential than under high substrate potential.Compared with B0 application,the application of B1 increased field holding(FC)by 14.6% and plant available water(AWC)by 28.9%,Compared with B0 application,the application of B2 increased FC by 9.91% and AWC by 21.6%.(2)Under the three irrigation levels of T0,T1,and T2,the soil bulk density decreased with the application of biochar,while the porosity increased with the application of biochar.Compared with CK(B0T1),adding biochar can reduce soil bulk density by 1.59–18.1%.With the same amount of biochar application,the amount of irrigation had no significant effect on soil bulk density and soil porosity.With the increase of the experiment period,a comparison of the soil bulk density and porosity for the same treatment before and after the experiment showed an increase in bulk density and a decrease in porosity in the vast majority of the soil.(3)The application of different biochar application and irrigation amount can change the particle size distribution of soil aggregates.The aggregates smaller than0.25 mm predominated,accounting for 85.19–87.91%.Secondly,there were aggregates of 0.25–2 mm,accounting for 7.19–9.44%.Compared with CK,the addition of biochar effectively increased the average soil weight diameter by 0.5–8.4% under T0,T1,and T2 irrigation.Under B2T0 treatment,the MWD value was the highest,reaching 0.4 mm,which increased by 8.70% compared to CK(B0T1).The amount of irrigation can affect the average soil weight diameter under the biochar application.Compared with CK(B0T1),adding biochar at T0 irrigation had a significant impact on soil stability.(4)Under the same soil water content and irrigation amount,the addition of biochar can reduce soil cohesion and increase internal friction angle.Under the same biochar application,reducing the irrigation water can weaken the cohesion of the soil,and increasing the irrigation amount can enhance the internal friction angle of the soil.The soil water content can affect the cohesion and internal friction angle of the soil.When the soil water content was 13%,the cohesion under B2T2 treatment was the highest,which was reduced by 38.57% compared to the maximum cohesion under CK(B0T1)treatment.When the soil water content was 5%,the internal friction angle under B2T0 treatment was the highest,which increased by 3.58% compared to the maximum internal friction angle under CK(B0T1)treatment.Adding biochar can reduce soil compaction,and at the same biochar application,T0 irrigation had the highest soil compaction.(5)The effect of biochar application on plant height was not significant,while irrigation amount had a significant impact on tomato plant height.The overall effect of biochar application and irrigation amount on tomato plant height was not significant.The maximum tomato plant height was measured under the B1T0 treatment,which was 12.82% higher compared to the control CK(B0T1).Under the same biochar application,there was a positive correlation between stem diameter and irrigation amount.The greatest increase in stem thickness was observed in the B1T0treatment(4.16 mm),which was 22.71% higher than the control CK(B0T1).Under B1T0 treatment,the yield of tomato was the highest,reaching 104.07 t/ha,which increased by 17.46% compared to CK(B0T1).(6)The six variables of bulk density,porosity,mean weight diameter(MWD),geometric mean diameter(GMD),maximum angle of internal friction,and maximum cohesion were selected as the evaluation indexes for the improvement of soil physical and mechanical properties at the harvesting period in 2022,and through comprehensive evaluation,it was found that the soil physical and mechanical properties under the B2T0 treatment were the best and the comprehensive scores of the soil with biochar addition were all higher than those of the soil without biochar addition.For the B0 application,the comprehensive score of the physical and mechanical properties of the soil under T1 irrigation was the best,followed by T2 irrigation,and finally T0 irrigation.For the B1 and B2 application,the soil physical and mechanical properties of T0 irrigation were the best,followed by T2 irrigation,and finally T1 irrigation.