Study On The Effect Of Mixed Biochar On Soil Water And Salt Transport In Gravel-mulched Fields

Gravel-mulched fields has a good effect of water storage and moisture conservation,temperature increase and evaporation reduction,so it can be widely used in the arid areas of Northwest China.However,with the increase of planting years,the effects of water retention,water storage,evaporation suppression and salt suppression are relatively weakened,and finally degradation occurs.As a special organic matter,biochar plays an active role in improving soil structure,regulating soil fertility and increasing crop yield.In view of this,the indoor soil column simulation test was used in this paper to study the influence of five different biochar treatment modes with sand mulching(T1),sand mulching+0.5%biochar(T2),sand mulching+1.5%biochar(T3),sand mulching+2.5%biochar(T4)and sand mulching+4.5%biochar(T5)on the water and salt migration rules of soil.The main research contents are as follows:(1)The effects of five different biochar treatment modes on water infiltration in soil were studied by simulated infiltration experiment.The results show that the relation between wetting front advance distance and time was a power function,and the decision coefficient R~2was between 0.975 and 0.983.The cumulative infiltration volume and time were consistent with Kostiakov infiltration model,and the decision coefficient R~2 was between 0.981 and0.994.The relationship between the wetting front advance distance and the cumulative infiltration was linear,and the decision coefficient R~2 was between 0.989 and 0.999.Compared with T1,T2 and T3 treatment modes increased the migration rate and cumulative infiltration of wetting fronts,while T4 and T5 treatment modes reduced the migration rate and cumulative infiltration of wetting fronts.(2)The effects of five different biochar treatment modes on water and salt transport in soil were studied by simulated evaporation experiment.The results showed that compared with T1,T2 and T3 treatment modes could promote water evaporation and salt surface accumulation in soil.T4 and T5 treatment modes had inhibitory effects on water evaporation and salt surface accumulation in soil,and the salt surface aggregation was T2>T3>T1>T4>T5.(3)Black evaporation model and Rose evaporation model were used to fit the relationship between water evaporation and time in soil.The results showed that both Black evaporation model and Rose evaporation model could well simulate the change rule of the cumulative evaporation amount after the application of biochar,and the decision coefficient R~2 was larger than 0.957.Compared with the Black evaporation model,the Rose evaporation model could more accurately reflect the variation rule of the water cumulative evaporation of soil by biochar,and the decision coefficient R~2 was between 0.978 and 0.986.(4)Through the electron microscope scanning method,the effects of five different biochar ratio processing modes on the fractal dimension value of soil and the correlation between different biochar ratios and different soil particle size volume fractions were comparatively studied.The results showed that the soil fractal dimension value and the percentage value of clay and powder particles under the two treatment modes of T2 and T3were all less than T1,and the biochar addition was negatively correlated with the fractal dimension value,clay volume fraction and powder particle volume fraction,and positively correlated with the sand particle volume fraction.In both T4 and T5 treatment modes,the fractal dimension value and the percentage value of clay and powder particles were greater than T1.Meanwhile,the biochar addition was positively correlated with the fractal dimension value,clay volume fraction and powder particle volume fraction,and negatively correlated with the sand particle volume fraction.