快速湿润过程中钾和钙离子浓度对土壤团聚体稳定性的影响

Effect of concentration of potassium and calcium cations on soil aggregates stability during fast wetting process

为探索土壤团聚体稳定性对电解质的响应情况,该文研究湖北省2种土地利用方式下(林地、耕地)的3种类型土壤(黄褐土、黄棕壤、棕红壤)团聚体,在不同浓度(0、0.005、0.01、0.02、0.05、0.08、0.10、0.20 mol/L)电解质(KNO_3、Ca(NO_3)_2)溶液中快速湿润时的稳定性和破碎过程。结果表明:1)浓度低于0.1 mol/L时,团聚体稳定性随电解质浓度增大而减小;2)团聚体稳定度AS随湿润时间呈双指数衰减,与纯水相比,棕红壤和林地黄褐土的破碎过程受电解质溶液影响尤为显著,黄褐土和耕地黄棕壤在电解质溶液中迅速全部破碎;3)初始阶段团聚体破碎能量与土壤粉粘比和有机质含量呈负相关,与铁铝氧化物含量呈正相关。总之,团聚体稳定性随电解质溶液浓度增大而减小,且相对于纯水,团聚体在电解质溶液中破碎更快。

Soil aggregates are basic properties of soil structure, and it is of very necessity to investigate soil aggregates stability when it comes to analyze the soil quality. At present, the soil aggregates are measured in medium of pure water, which ignores the existence of salt ions in soil water. Whereas, the soil water contains a variety of chemical substance. In addition, there is plentiful chemical substance in the irrigation water and fertilizer, which inevitably affects the stability of soil aggregates. Precipitation is abundant in Hubei area, and the alternation of rain and drought is also frequent. For investigating the effects of fertilization in droughty soil before irrigation or rainfall on the stability of soil aggregates, in this study, 2 different groups of experiments were carried out. In the first group, the soil aggregates from 3 types of soil （yellow cinnamon soil, yellow brown soil and brown red soil） in 2 kinds of land use types （forest and cultivated land） in Hubei Province were fast wetted under 2 kinds of electrolyte （KNO3 and Ca（NO3）2） solutions in different concentrations （0, 0.005, 0.01, 0.02, 0.05, 0.08, 0.10, 0.20 mol/L） and then washed by alcohol. MWD （mean weight diameter） values were calculated after wet sieving. In the second group, these air-dry soil aggregates were immersed under KNO3 and Ca（NO3）2 solutions with concentrations of 0, 0.05, 0.10 and 0.20 mol/L. The parameter values of the breaking energy of the aggregates at the initial stage） were assessed by double exponential fitting model of AS （percentage of intact aggregates in all the tested aggregates during wetting process） and wetting time. The results indicate that： 1） When the concentration of solution was lower than 0.1 mol/L, as electrolyte concentration increases, MWD value decreased and the aggregates tended to break down into smaller size fractions; 2） AS value exponentially decays as the wetting time. Compared with pure water, the crushing of the brown red soil and the forest yellow cinnamon soil was affected significantly by the electrolyte solution. The aggregates of yellow cinnamon soil and the yellow brown soil of the cultivated land were rapidly broken in the electrolyte solution; 3） The AS of aggregates was negatively correlated with the breaking energy of the aggregates at the initial stage, which is a parameter in the exponential model, and the crushing energy was negatively correlated with the ratio of silt to clay in soil and content of soil organic matter, while positively correlated with the content of oxidative iron and aluminum. In summary, while the concentration increases, the rate of solution penetrating into aggregates increases with the surface tension of solution. As a result, the stability of aggregates decreases when the solution concentration rises. And compared with pure water, aggregates are crushed faster under electrolyte solution. These findings demonstrate that the soil aggregates stability tested by medium of pure water is different from the actual situation in the field, which is helpful to provide practical reference for modern agricultural production. Considering the characteristics of fertilizer application in actual production, K＋ and Ca2＋ are selected as representative research objects. In further study, more kinds of salt cations can be tested to explore the effects of different kinds of cations on soil aggregates stability.