Preliminart Study Of Hofmeister Effect On Soil Aggregate Stability

.Soil aggregates stability affect the regulation of soil hea、water、gas and nutrient directly or indirectly, which also influence the occurrence of soil erosion and agricultural non-point source pollution. Improving the soil aggregates stability is one of the key aspects that improving soil fertility、ameliorating agricultural ecological environment、controlling agricultural non-point source pollution and occurring eutrophication.For a long time, academics believe the main reason for soil aggregates destruction which caused by precipitation is raindrops impact force on aggregate, also, academics neglect the influence of various inside forces. Soil particles are mainly in nano scale to micron scale. The behavior of mecroscopic particles is controled by hydration repulsive force, electrostatic repulsive force and van der waal’s force, which in combination determines the flocculation and dispersion of the soil colloid system. Hofmeister effects are also known as specific ion effects. They have a huge influence on the strength of soil electrostatic field,thus affecting soil particles interaction, finally, they will influence soil aggregates stability. However, Hofmeister effects have received much less attention from soil scientists. In the present paper, purple soil aggregates and yellow soil aggregates were employed as experimental materials and different ions species in soil solution were characterization Hofmeister effects, meanwhile the aggregate stability was quantified by measuring the number of soil particles (including micro-aggregates) with diameters of<10μm<5μm, and<2μm released when the aggregates were broken down.The main conclusions could be summarized as follows.(1) Hofmeister effects had strong impacts on purple soil aggregates stability. The released particles in all diameters were higher for NaNO3-aggregates than for KNO3-aggregates under different electrolyte solution concentrations. For example, the content of released particles in diameter of less than10μm were4-5times higher for NaNO3-aggregates than for KNO3-aggregates; it was5～11times higher for particles in diameter of less than5μm;5-8times higher for particles in diameter of less than2μm. Therefore, the breakdown process of NaNO3-aggregates was more intense while that of KNO3-aggregates were mild. Our experiments also testify that the stability differences between NaNO3-aggregates and KNO3-aggregates were much more significant when the concentration of the electrolyte solution was low, which directly negates the theory of ion hydration and dispersion force. Our experiments indicate that the differences between soil aggregates stability come from an amplification of the quantum fluctuation of ion electron cloud by soil surface electric field. When the concentration of the electrolyte solution is lower, the soil surface electric field strength is stronger. Finally, the stability differences between NaNO3-aggregates and KNO3-aggregates were bigger. Although we just studied Hofmeister effect on K+and Na+, it is reasonable to predict that Hofmeister effects impact soil aggregates stability in general.(2) Hofmeister effects had strong impacts on yellow soil aggregates stability. The different anions in potassium fertilizers, especially different phosphate ions will make a big difference in soil aggregate. So the use of potassium fertilizers bring multiplicity ecological and environmental problems. Cl had a good stabilizing effect on the yellow soil aggregates, whereas H2PO4-and HPO42-caused the aggregates to dissociate quite dramatically, releasing large amounts of<10μm,<5μm, and<2μm soil particles. The aggregate stability decreased significantly more in the presence of HPO42-than in the presence of HPO4-. We found that increases in the soil particle electrostatic fields are the fundamental causes of the loss of aggregate stability. The specific adsorption of H2PO4-or, especially, HPO42-significantly enhanced the electric field, decreasing aggregate stability. Our results suggest that aggregate stability is influenced by the specific adsorption of anions, with two important critical values, a critical concentration and a critical zeta potential. The critical electrolyte concentration was found to be approximately10-3mol/L, and the critical zeta potential was found to be approximately-30mV. The aggregate stability decreased sharply if the electrolyte concentration was decreased below10-3mol/L or the zeta potential increased above-30mV. We concluded that phosphorus is not only an important factor in the eutrophication of water bodies but is also an important driving factor in the destruction of soil aggregates, exacerbating the loss of phosphorus and other nutrients from soil.