Hydrogen peroxide and high-temperature heating differently alter the stability and aggregation of black soil colloids

Effects of Aerated Drip Irrigation on the Soil Nitrogen Distribution, Crop Growth, and Yield of Chili Peppers

In order to study the soil nitrogen (N) distribution pattern in the root zone of chili peppers under aerated drip irrigation (ADI) conditions and analyze the relationship between soil N distribution and crop growth, two irrigation methods (conventional drip irrigation and ADI) and three N levels (0, 140, and 210 kg hm-2) were set up in this experiment. Soil samples were collected by the soil auger method at the end of different reproductive periods, and the uniformity coefficient of soil N in the spatial distribution was calculated by the method of Christiansen's coefficient. The growth status and soil-related indices of pepper were determined at each sampling period, and the relationships between soil N distribution and chili pepper growth were obtained based on principal component analysis (PCA). The results showed that the spatial content of soil nitrate-N (NO3--N) fluctuated little during the whole reproductive period of chili peppers under ADI conditions, and the coefficient of uniformity of soil NO3--N content distribution increased by 5.29~37.63% compared with that of conventional drip irrigation. The aerated treatment increased the root length and surface area of chili peppers. In addition, the ADI treatments increased the plant height, stem diameter, root vigor, and leaf chlorophyll content to some extent compared with the nonaerated treatment. The results of PCA showed that the yield of chili peppers was positively correlated with the uniformity coefficient of soil NO3--N, root vigor, and root length. ADI can significantly improve the distribution uniformity of soil NO3--N and enhance the absorption and utilization of N by the root system, which in turn is conducive to the growth of the crop, the formation of yields, and the improvement of fruit quality.

Restricted colloidal-bound phosphorus release controlled by alternating flooding and drying cycles in an alkaline calcareous soil

Colloid-facilitated phosphorus (P) migration plays an important role in P loss from farmland to adjacent water bodies. However, the dynamics of colloidal P (Pcoll) release as influenced by irrigation in alkaline calcareous soil remains a knowledge gap. The present study, monitored the dynamic change of Pcoll under different water management strategies: 1) control, 2) flooding, and 3) alternating flooding and drying cycles. Soil water-dispersible colloids (0.6 nm-1 μm) were extracted by combining filtration and ultrafiltration methods. The contents of P, cation and organic carbon in the water-dispersible colloids were determined and the stability and mineral composition of colloidal fractions were characterized. The results showed that Pcoll ranged from 16.5 to 25.5 mg kg-1 and represented 42.8%-64.9% of the water-extracted P in the control. Flooding significantly decreased the Pcoll content by 16.0%-62.1% (mean 32.7%) and it may be attributed to the dissolution of colloidal iron (Fe) bound P. The alternating flooding and drying treatment significantly reduced the Pcoll content by 11.6%-88.0% (mean 67.6%). The Pcoll content of the flooding event was always greater than the Pcoll content of the drying event during flooding and drying cycles. Redundancy analysis and random forest modeling showed that the colloidal calcium (Ca) and ionic strength in soil solutions had negative correlations with the Pcoll content, and pH, ionic strength and truly dissolved P were the critical factors affecting Pcoll. Drying of the flooded soil led to the decrease of pH and the increase of ionic strength, colloidal Ca content and positive charges of colloid surfaces, which promoted colloid aggregation and enhanced soil P sorption capacity. This restricted the loss potential of Pcoll. In summary, controlled flooding and drainage when managed correctly have a role to play in mitigating Pcoll loss from P-enriched calcareous soils.

Temporal changes of exposure to water on physic-chemical, stability, and transport characteristics of pyrogenic carbon colloids

Understanding the effect of the aging process on the properties of pyrogenic carbon (PyC) is critical for predicting and evaluating its transport and fate. Water exposure is a common application scenario of PyC entering aquatic systems or flooded paddy fields, which might significantly affect the aging process. However, only some studies focused on the changes in PyC properties by water exposure treatment. In this study, the effect of water exposure on the mobility of PyC was investigated. Fresh PyC, PyC with 1.5 years and 3.5 years of water exposure were selected and named as CK, 1.5WA, and 3.5WA, respectively. Our results revealed that CK had the lowest intensity of surface functional groups (-OH, CO, and C-O-C) and the intensity of 3.5WA was higher than that of 1.5WA. There was no significant change in dissolved organic matter (DOM) content between fresh and aged PyC colloids. However, UV absorbance and its parameters (E2/E3, E4/E6, and SR) exhibited a comparable tendency to the abundance of functional groups (-OH, CO, and C-O-C). The fresh and aged PyC colloids showed high stability in Na+ and Ca2+ solutions at varying pH values (A/A0 > 85%), which was also observed in groundwater. The mobility of fresh and aged PyC colloids differed in Na+ (21.74%-57.19%), Ca2+ (14.30%-40.12%) solutions and groundwater (28.50%-44.24%), but exhibited similar order (3.5WA > 1.5WA > CK). The mechanism of the effect of water exposure on the property and mobility of PyC colloids was explored. This study provides the fundamental information to estimate PyC fate and transport after long-term water exposure.

Effect of reduced inherent organic matter on stability and transport behaviors of black soil colloids

Soil organic matter plays an important role in the stability, transport, and fate of soil colloids. At present, studies have mostly focused on the effects of adding exogenous organic matter on soil colloidal properties, while there is very limited research on the effect of reduced inherent soil organic matter on the environmental behavior of soil colloids. This study investigated the stability and transport behavior of black soil colloids (BSC) and black soil colloids with reduced inherent organic matter (BSC-ROM) under different ionic strength (5, 50 mM) and background solution pH (4.0, 7.0, and 9.0) conditions. Meanwhile, the release behavior of two soil colloids in the saturated sand column under transient ionic strength conditions was also studied. The results showed that both ionic strength reduction and pH increase increased the negative charges of BSC and BSC-ROM, and improved the electrostatic repulsion between soil colloids and grain surface, thereby promoting the stability and mobility of soil colloids. The decrease in inherent organic matter had little effect on the surface charge of soil colloids, suggesting that the electrostatic repulsive force was not the main force affecting the stability and mobility of BSC and BSC-ROM, and reducing inherent organic matter might significantly reduce the stability and mobility of soil colloids by weakening the steric hindrance interaction. The decrease of transient ionic strength reduced the depth of the energy minimum and activated the soil colloids retained on the surface of the grain at three pH conditions. This study is helpful to predict the potential impact of soil organic matter degradation on the fate of black soil colloids in natural environment system.

The Influence of Short-Term Heavy Rainfall on Hydraulic Characteristics and Rill Formation in the Yuanmou Dry-Hot Valley

Rill erosion is one of the major environmental problems in the world; it is an important factor with regard to land degradation and has a serious impact on production and daily life in the region. The widely distributed Yuanmou group stratum promotes the development of rill erosion, whereby the strong time-concentrated rainfall and the alternating arid-humid climate prepare the ground for the development of rills in soils. Therefore, a study of the processes of slope rill erosion was carried out, and a gravel-soil slope in the Yuanmou dry-hot valley was chosen to simulate short-term heavy rainfall (25 mm/h) (No. 1 plot) and moderate rainfall (15 mm/h) (No. 2 plot), to study the erosion processes of soil and the dynamic characteristics of runoff involved in erosion. The study results showed that the width of runoff was significantly different between the two plots, while the depth of runoff was not significantly different. During the rill formation process, the width of the two plots first decreased and then increased with increasing washout duration, while its depth did not change significantly. Flow was the key factor in determining the hydraulic characteristics of runoff, and it had a significant or extremely significant positive correlation with hydraulic characteristics parameters, except in the case of Fr (Froude number) (r = 0.039). The total sediment content (CS) of plot No. 1 (0.158 g/cm³) was significantly different from that of plot No. 2 (0.153 g/cm³), and both CSs in the two plots decreased with increasing washout duration. The CS had an extremely significant negative correlation with τ (runoff shear force) (r = -0.863 **) and DW-f (Darcy-Weisbach drag coefficient) (r = -0.863 **) and a significant negative correlation with Re (Reynolds number) (r = -0.735 *) in the short-term heavy rainfall experiment, while the CS had a significant positive correlation with V (velocity) (r = 0.814 *), R (hydraulic radius) (r = 0.811 *) and P (unit stream power) (r = 0.811 *) in the moderate rainfall experiment. The results of this study will help guide further examination of the processes involved in the dynamic mechanisms of rill erosion on slopes under short-term heavy rainfall conditions.

Aggregation kinetics of biochar nanoparticles in aqueous environment: Interplays of anion type and bovine serum albumin

The colloidal particles, especially those at the nanoscale, are the most active part of the pyrogenic carbon (biochar). Increasingly applied biochar has resulted in a large number of biochar nanoparticles (NPs) being released into the environment. The aggregation of biochar NPs affects their environmental behavior and fate. The complex effects of anion type (Cl^-, SO₄^2-) and protein (bovine serum albumin, BSA) on the aggregation of wheat straw biochar (WB) and pinewood biochar (PB) NPs in solutions were investigated by the time-resolved dynamic light scattering method. The critical coagulation concentration (CCC) of WB and PB NPs in Na₂SO₄ solution was higher than their CCCs in NaCl solution, which was consistent with the Hofmeister series that SO₄^2-, a kosmotrope anion, increased the interaction between water molecules, thus enhancing the hydrophobic interactions between biochar NPs in solution and promoting their aggregation, while Cl^-, a chaotropic agent, exhibited the opposite effect. When BSA was added into the solution, BSA was adsorbed on the surface of biochar NPs and BSA corona was formed, which inhibited the aggregation of biochar NPs by inducing steric force. The enhanced stability of biochar NPs by BSA was more significant in NaCl than in Na₂SO₄ solution because BSA corona had a more negatively charged surface and a more steric structure in NaCl solution, thus generating stronger electrical repulsion and steric hindrance. The classical DLVO theory and the XDLVO theory incorporating the steric repulsion (in the presence of BSA) were used to interpret the aggregation and dispersion of biochar NPs. Through this study, we found that anion type indirectly affected the aggregation of biochar NPs by influencing the interaction between water molecules, while the aggregation of BSA-biochar NPs conjugates is mainly influenced by the surface charge and structure of BSA corona.