Effect Of Biochar Addition Into Saline Soil On Hydraulic Conductivity And Air Permeability

The area of saline-alkali land in the Yellow River Delta reaches 4.3×10~5 hm~2,but also shows an increasing trend,which is an important land resource in the area.With the increasingly sharp contradictions between population growth and arable land reduction,the improvement and sustainable use of saline-alkali land has become an important way to ensure food security,improve the ecological environment and improve people’s quality of life.Coastal saline-alkali soil is easy to harden,water permeability is poor,water and fertilizer weak ability and other outstanding problems,seriously limiting the production potential of saline-alkali crops,becoming an important factor restricting the sustainable development of agriculture in the area.By applying biochar as an improver,the physical and chemical properties of coastal saline-alkali soil can be improved for the purpose of improving saline land.Through the indoor one-dimensional soil column simulation and indoor one-dimensional transient air conduction test,in this paper the effects of biochar addition amount and particle sizes of biochar on soil water and salt migration;With the addition of biochar,continuous infiltration and intermittent infiltration In filtration of water and salt transport contrast;The effects of biochar addition amo unton soil evaporation capacity and other aspects were analyzed and elaborated,to provide a theoretical basis for improving the coastal saline land.We get the following conclusions:(1)Through one-dimensional indoor soil infiltration test,the effects of different biochar addition amount and different particle sizes of biochar on soil infiltration capacity were studied.The results showed that biochar at the rate of 1%,2%,5%and10%could increase the infiltration capacity of soil water,and with the increase of biochar,the infiltration capacity was stronger.Biochar addition promoted the wetting front migration and shortened the infiltration duration,compared with the control,infiltration into the bottom of soil column,the infiltration time of biochar at the rate of5%and 10%were shortened by 18.46%,21.54%;The cumulative infiltration was increased when biochar added into the soil,compared with the control,the cumulative infiltration of biochar at the rate of 5%and 10%were increased by 15.80%and 20.90%respectively at 180min.≤0.25mm,0.25-1mm,1-2mm 3 kinds of biochar particle size addition treatment of 1%and 10%biochar addition amount can promote soil infiltration capacity,the smaller the particle size,the stronger the infiltration,and can promote the wetting front migration,shorten infiltration duration,increase soil infiltration,such as180min,compared with the control,The cumulative infiltration of biochar three size(≤0.25mm,0.25-1mm,1-2mm)at the rate of 10%were increased by 49.66%,44.72%and 23.15%respectively.By fitting the relationship between wetting front migration distance and time,the power function is better with the determination coefficient above 0.999.By fitting Philip and Kostiakov infiltration models to the relationship between cumulative infiltration and time,the fitting coefficients of Philip and Kostiakov infiltration models were both above 0.99.Based on the further analysis of fitting parameters,Philip Infiltration model fited better.(2)Through the indoor soil column test,the effects of continuous infiltration and intermittent infiltration on the movement of soil water and salt were compared and analyzed under the biochar addition.The results showed that 1%and 5%biochar addition treatments could promote soil water transport,and the 5%biochar addition treatment effect was more obvious.Under the same biochar adding amount,the water content of each soil infiltrated intermittently was higher than that of continuous infiltration.The water content of intermittent infiltration treated with 5%biochar was higher than that of continuous infiltration of 13.06%~23.11%.The effect of continuous infiltration and intermittent infiltration on soil salinity showed that compared with the control,the leaching effect of 1%biochar addition was not good and the leaching effect of 5%biochar addition treatment was good and could be reduced salt in the soil.Under the same biochar addition amount,the leaching effect of intermittent leaching on topsoil(above 41cm soil layer)was better than that of continuous infiltration.The intermittent infiltration of salt in plow layer was lower than that of continuous infiltration,but intermittent infiltration the large amount of salt accumulated to the bottom of the soil,so the bottom of the salt content of intermittent infiltration is higher than the continuous infiltration.(3)Through indoor soil column test,the effect of biochar addition on the evaporation was studied.The addition of biochar could restrain the evaporation of soil moisture.The biochar at the rate of 1%inhibited the evaporation of water more effectively and reduced the evaporation,and at the rate of 5%biochar was not significantly different from control.The addition of biochar also had an impact on the soil salinity.Through the analysis of electric conductivity,the treatment of 1%biochar increased the surface aggregation of soil salinity,and the treatment of 5%biochar reduced the soil salinity.(4)The effect of different biochar additions amount and biochar particle size on the gas permeability of saline-alkali soil was studied by indoor one-dimensional transient gas conduction test.The results showed that the air permeability increased with the biochar addition,and the air permeability of the biochar at the rate of 10%was 72.73%higher than that of the control.Medium and large particle size biochar effect on the improvement of soil air permeability is very significant,Which can significantly improve the permeability of the soil.Biochar addition amount,biochar particle size and air permeability were significantly exponential function.