Pedogenesis significantly decreases the stability of water-dispersible soil colloids in a humid tropical region

Abstract

The stability of soil colloids influences soil physicochemical properties, soil development, and transfer of nutrients and contaminants to surface and ground waters. A better understanding of soil colloids stability dynamics during soil evolution is important for the evaluation of soil's capacity to retain nutrients and/or accommodate toxic contaminants. This study was aimed to determine changes in the stability of water-dispersible soil colloids that accompany mineral transformation and surface charge evolution during pedogenesis using a well characterized chronosequence derived from basalt in the humid tropical region of Hainan Island, South China. The results demonstrated that the pH-dependent colloid stability decreased significantly with tropical soil development, which we attribute to the substantial changes in clay mineral compositions and colloid surface charge properties. Clay minerals in the studied chronosequence were characterized by an increase of kaolinite, gibbsite and Fe oxides and a decrease of quartz and halloysite towards more advanced stages of weathering, which resulted in the decline of permanent negative charges in the older soils. The point of zero charge (pH PZC ) increased while ΔpH decreased across the tropical soil chronosequence, being in good agreement with the observed lower colloid stability in aged soils dominated by kaolinitic minerals. Our study of colloid stability at long-term pedogenic time scale suggests young tropical soils (b 180 ka) with high surface charge are subjected to higher risk of clay movement and colloid-facilitated nutrients and contaminants transport. Careful management practices are thus required to avoid colloids dispersion and transport in young tropical soils either by reducing the frequency/intensity of pore-water flow or by liming to counter the high permanent negative charges.

New Straw Coating Material for Improving the Slow-Release Performance of Fertilizers

“…Inorganic molecules in clay can be interconnected through electrostatic attraction, thereby increasing the hardness of particles. The adsorption characteristics of clay also delayed the release of nutrients. ,− The clay used for granulation in this study contained 80% kaolinite (Table S1), and there was an intercalation phenomenon between kaolinite layers in the urea-water system (Figure S4). Studies have shown that the urea molecules between the kaolinite interlayer were distributed in double layers; the N–H bond and the C–O bond in urea have formed hydrogen bonds with the O–Si and H–O–Al on the upper and lower surfaces of the kaolinite, respectively; the water molecules between the kaolinite interlayer were distributed in three layers; and a small amount of water molecules were adsorbed on the kaolinite’s surface by generating hydrogen bonds (O–H–O–Si) with O–Si bonds, which protected the urea molecules from water immersion and prolonged the time of nutrient release.…”

Effects of Organic Wastes on Soil Organic Carbon and Surface Charge Properties in Primary Saline-alkali Soil

“…Wu, Liu, Li [64] found that more than 75% variable surface charge originated from soil organic matter. The reason why soil SOC and Fr-LFOC affect surface charge properties is that soil organic carbon is usually negatively charged, and studies have shown that every 1% increase in organic carbon content, can increase the soil charge by 1 cmol·kg −1 [65]. Soil organic carbon is generally present in organic colloids, and the organic colloid is an amphoteric colloid [66].…”

Evaluation of the Continuous Application of Different Organic Materials on Soil Surface Charge and Chemical Properties Along the Soil Profile of a Typical Mollisol

“…4). This could mainly be due to the reduced organic matter along the profile as previous reports indicated that the removal of organic matter from the soil directly reduced the SSA of the soil due to a reduction in the content of soil organic colloids (which are known to have larger surface area than the inorganic minerals in the soil) [73,74].…”