| In this study,loessial soil,typical soils of the Loess Plateau,was used to cultivate soil and soil aggregates of different soil layers with different particle sizes using PAM,humic acid,chitosan and aluminum sulfate.The effects of mechanism on the structure,the pore characteristics of aggregates and the distribution of organic matter on aggregates with different particle size were studied.The main conclusions are as follows:(1)All kinds of cementing agents can increase the content of>0.25 mm aggregates and the mean weight diameter(MWD)of soil aggregates as well,the two were positively correlated,with the improvement of soil structure and soil function.PAM had a significant effect on the improvement of mean weight diameter of the whole soil and <0.25 mm aggregates at the concentration of 0.1% for two weeks,but the effect of the culture time on the structural characteristics was not significant.For 1 ~ 0.25 mm aggregates,results showed that the improvement of the structural characteristics was obvious,while for 2 ~ 1 mm aggregates was content more than 0.2%,or the time was more than one month.The incubation time had obvious influence for particles for 2 ~ 1 mm and 1 ~ 0.25 mm aggregates.The effect of humic acid on the structural characteristics of 2 ~ 1 mm aggregates can be achieved at a concentration of 0.4% or more in a short time,but the effect can be improved by 0.1% at the time of long-term culture and the effect was not significant with time.The results showed that the effect of 1 ~ 0.25 mm and <0.25 mm aggregates changed with the increase of culture time.For 1 ~ 0.25 mm aggregates,the concentration was>0.2% for more than two months will have significant effects.The improvement effect of chitosan on the structural characteristics of soil topsoil varies with the concentration gradient,and the effect of the improvement of the incubation time is obvious.For the 2 ~ 1 mm and 1 ~ 0.25 mm aggregates,the improvement of the structural characteristics changed significantly with time,and the effect was obvious at the concentration of 0.1% for two months.While at 0.2%,it only took one month.The structural characteristics of the <0.25 mm aggregates were improved at a concentration of 0.1% for two weeks to reach a significant level.The effect of aluminum sulfate on the structural characteristics of the whole soil,2 ~ 1 mm and 1 ~ 0.25 mm aggregates changed with time,and the structural characteristics of 2 ~ 1 mm and 1 ~ 0.25 mm aggregates were improved only after culture for two months.While for <0.25 mm aggregates structure,the effect is not obvious.In summary,the effect of different cementing agents on the structural characteristics of soil aggregates was PAM > humic acid > chitosan > aluminium sulfate under the test concentration(0.1% ~ 0.4%);<0.25 mm aggregates had the best effect,followed by the whole soil,2 ~ 1 mm and 1 ~ 0.25 mm aggregate effect was relatively poor.This is because the two particle size aggregates in the culture process,small particle size aggregates in the role of organic matter and other bonding together to form large aggregates,and large particle size of the aggregates are broken into small agglomerates,the two interact with each other,make the overall change is not obvious.(2)After adding four kinds of cementing agents,the content of organic matter in the aggregates of the topsoil was significantly higher than that of the bottom soil.The effect of cementing agent on the organic matter content in the subsoil was more obvious.After treatment with PAM,the content of organic matter on 5 ~ 2 mm aggregates increased with the increase of culture time,and reached a significant level when compared with the control at the concentration of 0.1% for two weeks.The difference of organic matter content after two weeks of 2 ~ 1 mm aggregate was reached significant level in concentration >0.2%,and after two months was significantly different when concentration was 0.1%.The content of organic matter on the <0.25 mm aggregates was significantly different from that of the control after incubation for four months at the concentration of 0.2%,and the difference was significant at the concentration of 0.2% value.After the application of humic acid,the content of organic matter on 5 ~ 2 mm aggregates did not change significantly with the culture time,and the concentration of 0.1% after two weeks was significantly different from that of the control.The difference of organic matter content was significant at the concentration of >0.2% after two weeks in 2 ~ 1 mm aggregates,and the difference was significant at the concentration of 0.1% for a month.The content of organic matter on the <0.25 mm agglomerates was significantly different from that of the control at the concentration of 0.1% for two weeks.After applying chitosan,the difference of organic matter content in 5 ~ 2 mm aggregates under different culture time is not large,0.2% concentration of two weeks of culture compared with the control reached a significant level,0.1% concentration of one month,the difference was remarkable.The difference of organic matter content in 2 ~ 1 mm aggregates was significant at the concentration of 0.4% for two weeks,and the difference was significant at the concentration of 0.1% for one month.The difference of organic matter content on the <0.25 mm aggregates was significant at the concentration of 0.1% for two weeks,it reached a significant level compared with the control.From the analysis above,the content of organic matter in the aggregates with different particle size increases with the increase of the concentration of cement,and the suitable binder concentration is 0.2% ~ 0.4%.The suitable culture time is two month;chitosan has the best comprehensive effect,the effect is significant,followed by PAM,the worst is humic acid;the organic matter content on 5 ~ 2 mm and 2 ~ 1 mm aggregates was significantly higher than <0.25 mm aggregates.(3)The four kinds of cementing agents can improve the total porosity of the aggregates,increase the porosity of ventilation and narrow pores,and have the effect of improving the soil permeability.PAM has a great influence on the pore characteristics and the pore size distribution of aggregates.The effect of humic acid and aluminum sulfate on the pore characteristics and pore size distribution of aggregates is limited.Chitosan reduces the porosity of regular pores and capillary pores with remarkable effect.When for short time culture,PAM,humic acid,chitosan on the aggregates of the pores can play a good role in improving,while the aluminum sulfate culture after one month to have effect. |
PDF Full Text Request