Positoining Research On The Effects Of Soil Amendments Addition On Soil Pore Structure And Water Process

Soil amendments have shown great potential in improving soil structure,soil moisture,nutrients and gas retention.However,systematic studies on the effects of soil amendments on soil pore structure and water movement have not been carried out,and are mainly limited to indoor simulation studies.Due to the difference in the densities of soil and amendment and the unstable measurement of the bulk density(BD)over time after the amendments were applied,the effect of the amendments on the bulk density and the porosity has been rarely expressed accurately.In this study,the effect of the three common soil amendments,i.e.biochar,grass peat and weathered coal at 26,52 and 78 t/ha with three replicates on soil pore structure and water movement and their time effect was investigated by measuring the BD,aggregates,porosity,saturated hydraulic conductivity(Ks),soil water characteristic curve(SWCC)and soil temperature and soil moisture at different times of one year based on field experiments.The purpose of this paper was to provide theoretical support for improving soil structure and water movement,and to promote the in-depth study of the ecological effects of soil amendments on returned soils in semi-arid areas.The results are as follows:(1)The addition of three soil amendments,biochar,gras peat and weathered coal,significantly reduced BD in the past one year.The reduction effect of biochar on BD was better than that of grass peat and weathered coal,and it was proportional to the additions.The change of time has a significant effect on BD and each of the treatment increases first and then decreases in one year.There was no significant difference in the aggregates content of 0.25-5mm,MWD and GMD(except for grass peat treatments in day2)between different treatments within one year.The content and stability of soil aggregates were increased in the later stage after the addition of soil amendments.Aggregate content,MWD and GMD decreased first and then increased with time,and there was a significant negative correlation between them and BD.The application of the soil amendments significantly increased the total porosity of the soil,and the difference in the porosity of all treatments was primarily attributed to the macropores change.The increase effect of biochar on the total porosity was the most obvious,and it was proportional to the additions.The calculated total porosity calculated from the apparent BD was greater than the measured total porosity indirectly derived from the soil water characteristic curve by 2.71%.The effect of the time factor on the measured total porosity was not statistically significant.The pore size distribution of different treatments was ultra microporous(26.35-26.92%)> mesoporous(9.83-10.54%)> microporous(7.08-7.60%)> macroporous(2.61-4.01%).The increase of BD was mainly due to the increase of ultramicropores,the decrease of micropores and macropores,while the decrease of BD was mainly due to the increase of mesopores and macropores.(2)Although the Ks was increased for the grass peat and decreased for the biochar and the weathered coal within one year,the difference did not reach a significant level compared to CK,nevertheless the effect of time on the Ks was significant.The Ks of all treatments decrease first and then increase with time but was always lower than the initial value.The SWCC showed that the water loss was mainly in the low suction(0-1000 cm water column),and there was no significant difference in soil water curve among different treatments.The parameters of Van Genuechten model were obtained by RETC software,which showed that the addition soil amendments improved the drainage capacity of soil,made the particle size distribution more uniform and improved the water holding capacity of soil to to some extent.(3)The addition of soil amendments can increase soil temperature to some extent,but its impact was limited.Grass peat and weathered coal treatments increased the soil temperature and activity accumulated temperature,while biochar had no obvious effect on soil surface temperature.Biochar can moderate the extreme temperature of the soil,and the average daily temperature relaxation ability of the soil was in the range of-0.45?to 1.22?.In summer and winter,the average soil temperature of different treatments reached the highest at 15-16 o'clock in a day,and the difference of was the greatest.The lowest soil temperature in summer and winter was 7-8 o'clock,and the difference was the smallest.Biochar treatment greatly increased the average soil moisture,weathered coal had little effect on soil moisture,and grass peat reduced the average soil moisture.In summer,the highest moisture content was between 2 and 3 o'clock,the lowest was between 16 and 17 o'clock,and in winter,the highest moisture content is between 1 and 2 o'clock,and the lowest is between 11 and 12 o'clock.The change range of soil average temperature in summer and winter is larger than that of soil average moisture.