| Aggregate stability is closely related to soil nutrient loss and farmland non-point source pollution, In the progress of rainfall or irrigation, amounts of microaggregates and single grains are released when soil aggregates break in violent way in water. It forms suspension in water, and then induces soil and water loss in the migrant function of Brown force, and thereby it walks away with great nutrients in the migrant progress. It causes water eutrophication when it flows in the water body. Finally, the environment of water, soil and atmosphere are destroyed, which threaten the human health.In order to counteract the aggregates breakdown and prevent the environment pollution from being worse, it’s an effective measure to improve the stability of aggregates. At present, organic matter makes a crucial effect in the study of improving aggregates stability causes. It is generally believed that including the organic matter, the humus induced the soil particles aggregating by the way as a cementing agent, and that it come true through the "bridging" effect of the polyacrylamide (PAM). Indeed, these whole studies could be explained to some extent the reason of improving the aggregates stability by organic matter. However, it is a complicated progress of the soil particles aggregate in the liquid water system, the existed shape of the humus in the water is also granular, and the aggregate format between soil and humus particle should be colloid aggregate. Thus, it is not integrative to the claim that soil particles aggregate just because of humus (cementing agent), and because of PAM (bridging effect). Because it exist the electrostatic field stabilizing effect among the colloid particles, and the cohesion between the soil colloid particles and humus/PAM whould follow the effect. Consequently, it needs to explore in depth the detailed mechanism of promoting aggregates stability by humus and PAM in the electrostatic field. Whereas owing to studies, the correction theories of soil particles interactional effect depending on the electrostatic field has been established by Li hang et al, and thereby it become a possible for people to reveal these mechanism.Therefor, we made studies about the effect of the coupling of electric field and organic macromolecules (the humus and PAM) on soil aggregate stability. Different concentrations of Ca(NO3)2, KNO3and NaNO3solutions were used to adjust the strength of soil electric field in the experiment and the molecular attraction forces among the soil particles were controlled by the content of humus and PAM. The aggregate stability was indicated by the content of released particles in diameter of<10,<5and<2μm after aggregate breakdown. In addition, we made an experiment about the colloid particles interaction between soil and humus by the dynamic light scattering technique. In the end, we made an integrate analysis about the different stability mechanism between the humus and PAM. The primary conclusions as follows:(1) Soil electric field played a crucial role in aggregate breaking. When the electric field was high, no matter whether the organic macromolecules were added or not, aggregate breakdown happened in violent way and released amounts of microaggregates and single grains; when the electric field was lower, the result was reversely. Under the same soil electric field strength, when humus and PAM were added in the Ca2＋/K＋/Na＋-aggregates, there was a highly decrease of the degree of aggregates breakdown, and the highly decrease of critical surface potential in the form of aggregates explosion.(2) The quantum fluctuation coupling effect between ions and external electric field would bring a large difference for the aggregates stability in homovalent ions system, and finally the intensity of the aggregates breaking was different. Because of the existed specific ion effect, though K＋/Na＋ions were all univalent ion, the stability of the formed K＋-aggregate was stronger than the Na＋-aggregate. Accordingly, no matter whether the humus and PAM included or not, the breaking intensity of K+-aggregate was lower than Na＋-aggregate. Moreover, because the capability of shielding on surface electric charge around the particles of Ca2＋ions was higher than K+/Na＋ions, in the effect of soil electric field, the breaking intensity of Ca2＋-system aggregates and the content of the released microaggregates and single grains were all lower than K+/Na+-system. So in the K+/Na+/Ca2+-aggregates, the capability of inducing aggregate breakdown present a sequence of Na＋> K＋> Ca2＋.(3) The analysis of the coupling effect between soil and humus by the dynamic light scattering effect showed that:it made a strong effect for aggregate stability among the soil electric field, specific ion effect, and humus. Firstly, owing to the electrolyte concentration increasing, the soil electric field strength had decreased. Thus, no matter the K＋-/Na＋-colloid system included humus or not, the average aggregate rates had increased. Secondly, when the content of humus in the K＋-/Na＋-system of the colloid particles was zero, the maximum particle size of Na+-aggregate (1710nm) was higher than K＋-aggregate(1350nm). No matter the K＋-/Na＋-colloid system included humus or not, the average aggregate rates of the K+-system were greater than Na＋-system. It showed that the aggregate progress of K＋-/Na＋-colloid system exhibited an obviously difference of the specific ion effect. Lastly, because the content of humus was added increasingly, the capacity of the negative electric charge increased, and thereby the stability of the colloid particles system was enhanced. Then the lowest electrolyte concentration for the colloid particles aggregating was needed. At the meantime, the average aggregate rates had decreased.(4) Humus and PAM were granular and linear molecule organic matters respectively. When humus/PAM coupled with soil electric field, the stability strength of the aggregate had evident differences. The discrepancy mainly showed that:The differences mainly exhibited that:the content of the humus in the aggregates was increasing, the aggregate stability was enhanced; a feasible PAM concentration in the aggregates could make a best effect for aggregate stability, but it would not increase when the content of PAM was higher than the feasible concentration, In this paper, the feasible PAM concentration was0.03%, and then it made a best effect for preventing aggregate breaking. The different coupling extent between the electric field and humus/PAM brought to the clear differences in the breakdown processes. Under the same electric field strength, the breaking strength of Ca2＋/K＋-humus-aggregates and Ca2＋/K＋-PAM-aggregates decreased by～80%and～60%, respectively. Comparing with humus, PAM could evidently increase stability of Na＋-aggregate (which was weak stability), the breaking strength decreased by90%. |
PDF Full Text Request