Effect Of Exogenous Additives On Physical Properties Of Loessial Soil

Exogenous additives have great potential to change the physical and chemical properties of the soil,prevent soil degradation,save agricultural irrigation water and promote the healthy growth of crops.Exogenous additives made from agricultural and industrial wastes are also conducive to promoting circular agriculture and improving the additional economy growth.Which will have a broad application prospects in adjusting the structure of loessal soil and improving the performance of water and fertilizer retaining.In this experiment,15 g/kg,35 g/kg and 35 g/kg dry weight biochar and woody peat,87.5 g/kg,175 g/kg and 262.5 g/kg wet weight drilling mud were added into loessial soil,in order to explore the effects of additives materials on the texture,bulk density,total porosity,saturated hydraulic conductivity,relative gas diffusivity,soil moisture characteristic curve and evaporation characteristics and providing theoretical basis for waste recycling.The main conclusions are as follows:(1)Biochar,woody peat and drilling mud can reduce the content of loamy sand and increase the content of clay and silt.The addition of exogenous materials all reduced the bulk density of loessial soil,except for the addition of 262.5 g / kg drilling mud,the other treatments were significantly different(P <0.05).As the proportion of biochar and woody peat increases,the effect of lowering the bulk density is better,while the drilling mud’s effect on the bulk density of loess soil as the proportion of addition increases first and then decreases slightly.Among the three kinds of exogenous sources,the best effect of reducing bulk density is woody peat(reduced by 7.9% ～ 17.1%),followed by biochar(reduced by 6.3% ～ 13.1%),and finally drilling mud(reduced by 1.8% ～ 5.5%).Among the treatments of additives,55 g/kg woody peat had the biggest influence on bulk density which reduces the bulk density by 17.1%.The rugularity of the total porosity of loess soil is similar to the bulk dendity.Exogenous additives all significantly reduced the saturated hydraulic conductivity(P <0.05),the more additives,the lower the hydraulic conductivity of loessial soil.The best effect is drilling mud(reduced by 63.3% ～ 95.6%),followed by woody peat(reduced by 24.1% ～ 68.5%),followed by biochar(reduced by 17.2% ～ 74.1%).Among the treatments of additives,262.5 g/kg of drilling mud had the biggest influence on saturated hydraulic conductivity which reduces the saturated hydraulic conductivity by 95.6%.The relative gas diffusivity is sensitive to soil water content,and the effect of each treatment is related to the water content,the overall difference is not significant(P <0.05).(2)The influence of exogenous additives on the soil moisture characteristic curve has two sides.Only the addition of 35g/kg biochar,35g/kg and 55g/kg woody peat,175g/kg and 262.5g/kg drilling mud enhanced the water retention.with the increase of biochar,The water retention ability decreases first and then increases and then decreases,and it would decreases and then increases with more woody peat and drilling mud added,the impact on water retention is different at different suction stages.With the drying of the soil,it is conducive to the moisture retention when adding 35g/kg of biochar in the higher water suction section,the remaining additives treatment inhibits the water retention.The VG model can better simulate the soil moisture characteristic curve.In this paper,it is found that the hysteresis of the soil moisture characteristic curve may be related to the parameters α and n,the smaller the α,the bigger the n,the greater the hysteresis.(3)It was found that the addition of biochar had no significant effect on the evaporation characteristics by the indoor soil column simulated evaporation test.The addition of woody peat can inhibit the evaporation,but regularity needs further study.The addition of drilling mud inhibited the evaporation and the inhibitory effect became more obvious as the added amount increased.