Soil Carbon Sink Effect of Main Management Models in Typical Granite Erosion Area of Red Soil in South China

Uranium-contaminated wastewater associated with uranium (U) mining and processing inevitably releases into soil environment. In order to assess the risk of U wastewater contamination to groundwater through percolation, U adsorption and transport behavior in a typical red soil in South China was investigated through batch adsorption and column experiments, and initial pH and carbonate concentration were considered of the high-sulfate background electrolyte solution. Results demonstrated that U adsorption isotherms followed the Freundlich model. The adsorption of U to red soil significantly decreased with the decrease of the initial pH from 7 to 3 in the absence of carbonate, protonation-deprotonation reactions controlled the adsorption capacity, and lnCs had a linear relationship with the equilibrium pH (pHeq). In the presence of carbonate, the adsorption was much greater than that in the absence of carbonate owing to the pHeq values buffered by carbonate, but the adsorption decreased with the increase of the carbonate concentration from 3.5 to 6.5 mM. Additionally, the breakthrough curves (BTCs) obtained by column experiments showed that large numbers of H+ and CO32- competed with the U species for adsorption sites, which resulted in BTC overshoot (C/C0 > 1). Numerical simulation results indicated that the BTCs at initial pH 4 and 5 could be well simulated by two-site chemical non-equilibrium model (CNEM), whereas the BTCs of varying initial carbonate concentrations were suitable for one-site CNEM. The fractions of equilibrium adsorption sites (f) seemed to correlate with the fractions of positively charged complexes of U species in solution. The values of partition coefficients (kd') were lower than those measured in batch adsorption experiments, but they had the same variation trend. The values of first-order rate coefficient (ω) for all BTCs were low, representing a relatively slow equilibrium between U in the liquid and solid phases. In conclusion, the mobility of U in the red soil increased with the decrease of the initial pH and with the increase of the initial carbonate concentrations.

Construction and evaluation of pedotransfer functions for saturated hydraulic conductivity in the granite red soil regions of southern China

亚热带典型红壤侵蚀区人类活动对植被覆盖度及景观格局的影响

Reforestation of Pinus massoniana alters soil organic carbon and nitrogen dynamics in eroded soil in south China

Perennial energy crops (PECs) such as Miscanthus spp. and switchgrass (Panicum virgatum L.) may have particular influence on microbial communities and their functions in soil organic carbon (C) utilization and mineralization (Cm). In this study, long‐term effects of PECs on Cm and soil hydrolase activities were examined in bulk and rhizosphere soils of Miscanthus and switchgrass grown on a red soil in South China. Long‐term cultivation (10 years) of PECs led to increases in soil organic C (SOC) and the absolute Cm of bulk and rhizosphere soils. Total Cm was correlated with dissolved organic C and dissolved organic nitrogen (N) in red soils. The specific Cm in bulk soils of switchgrass and Miscanthus were decreased by 11.73% and 20.67% comparing with the control group, respectively. Cultivation of PECs led to a relatively high C/N ratio. There was a difference in priming effect on activities of β‐glucosidase (BG), leucine amin peptidase, N‐acetyl‐β‐glucosaminidase (NAG), and phosphatase between rhizosphere and bulk soils. Compared with the control without PECs, BG activity did not change significantly in bulk soils of PECs, whereas NAG activity decreased significantly. Soil microorganisms were generally limited by soil C and phosphorus (P) in the red soil. The C and P limitations were significantly linearly related with relative Cm (p < 0.05). Phosphorus limitations in microbial communities were lower with PECs than in the control, indicating that cultivation of PECs could provide an optimal nutrient environment for both plants and microorganisms. Thus, long‐term cultivation of PECs increased SOC content but decreased specific Cm rates. However, because C and P limitations remain for plants and soil microbial communities, optimum fertilization is also necessary for sustainable growth of PECs on red soils.

Mechanisms of biochar effects on thermal properties of red soil in south China

Understanding the underlying mechanism of soil carbon (C) and nitrogen (N) accumulation is of great significance for soil C sequestration and climate change mitigation, as well as soil fertility improvement. The objective of this study was to evaluate the response of C and N accumulation in aggregates and fine soil particles to long-term mineral fertilizer and manure application. Five treatments from a long-term experiment with double maize cropping were examined in this study, i.e., (1) no fertilizer (control); (2) mineral nitrogen, phosphorus, and potassium application (NPK); (3) doubled application rate of the NPK (2NPK); (4) pig manure alone (M); and (5) mineral NPK fertilizers and manure combination (NPKM). By using physical particle-sized fractionation, we analyzed soil organic carbon (OC) and total nitrogen (N), and δ13C of OC in bulk soil and aggregates (53–2000 μm) and, coarse silt-sized fraction (5–53 μm), fine silt-sized fraction (2–5 μm), and clay-sized fraction (< 2 μm) under those five treatments. Fertilizer application for 24 years, particularly M and NPKM treatments, significantly increased the concentration and proportion of OC and total N associated with aggregates and clay-sized fraction as compared with control. Manure application significantly increased the proportion of OC by 6.6–7.8 points in aggregates, whereas it was by 22.6–25.0 points in clay-sized fraction. Clay-sized fraction-associated C and N showed a non-linear response to C and N accumulation in bulk soil, contributing approximately 47% and 69% to soil OC and total N, respectively. Moreover, the mass proportion of aggregates and the mass ratio of aggregates to fine soil particles increased significantly with C accumulation in fine silt-sized and clay-sized fraction. Organic carbon and total nitrogen accumulation in soil clay-sized particles play important role in soil C and N sequestration in red soil. Our results also suggested that C accumulation in fine soil particles might benefit soil aggregation in intensive cropping system of South China.

Plantation type and age strongly influence the quantity of carbon stored in forest ecosystems. The marked increase in total ecosystem carbon stock achieved over time by the Eucalyptus and Acacia plantations has confirmed that the afforestation of degraded soils can contribute positively to carbon sequestration. Reforestation has been widely conducted to restore and protect the eroded red soil in south China in recent decades. The question as to whether the content of soil organic carbon (SOC) can be boosted by establishing plantations of fast-growing tree species remains unresolved. We addressed whether the afforestation of degraded soils can contribute positively to carbon sequestration, and whether the accumulation of SOC is more effective under a nitrogen fixing species such as Acacia than under Eucalyptus. Here, a study was undertaken to measure the quantity of total ecosystem carbon (TEC) accumulated by plantations of both Eucalyptus and Acacia spp. in the Pearl River Delta region of southern China. The quantity of TEC increased significantly with stand age in both plantation types (P < 0.05). The largest single component of TEC was SOC, with stand age having a considerable effect on both SOC and overall biomass. The accumulation of SOC in the top 100 cm of the soil profile was higher under Acacia than under Eucalyptus (P < 0.05). In terms of carbon sequestration, the afforestation of Eucalyptus and Acacia represent an effective forest management practice. The accumulation of SOC is more effective under Acacia than under Eucalyptus.

Rapid industrial development in the old northeastern industrial region of China resulted in Hg pollution. A series of batch experiments were conducted to assess the adsorption/ desorption and transfer of Hg (II) within typical black soil in this region and typical red soil in south China as a comparison: both are typical soils in China. It was found that both soils had high affinity for Hg (II) and the absorbed amount was more than 95% of the added. Hg (II) adsorption isotherms were well fitted with the Langmuir and Freundlich equations. The affinity of Hg (II) for black soil was three times higher than that of red soil. Results demonstrated that soil organic matter had an important role in Hg (II) adsorption. Fifty-three and twenty-eight percent of the maximum sorption amount for Hg (II) was contributed by organic matter for black soil and red soil, respectively. Kinetic studies showed that Hg adsorption on both soils was characterized by a biphasic pattern, with a fast step followed by a slow step. Black soil completed 90% of total Hg (II) adsorption in 34 min and reached equilibrium in 321 min, compared to 91 min and 630 min on red soil, respectively.

A detailed study on the solution chemistry of red soil in South China is presented. Data are collected from two simulated column-leaching experiments with an improved setup to evaluate the effects of atmospheric N deposition (ADN) composition and ADN flux on agricultural soil acidification using a (15)N tracer technique and an in situ soil solution sampler. The results show that solution pH values decline regardless of the increase of the NH4(+)/NO3(-) ratio in the ADN composition or ADN flux, while exchangeable Al(3+), Ca(2+), Mg(2+), and K(+) concentrations increase at different soil depths (20, 40, and 60 cm). Compared with the control, ADN (60 kg per ha per year N, NH4(+)/NO3(-) ratio of 2 : 1) decreases solution pH values, increases solution concentrations of NO3(-)-N, Al(3+), Ca(2+) and Mg(2+) at the middle and lower soil depths, and promotes their removal. NH4(+)-N was not detected in red soil solutions of all the three soil layers, which might be attributed to effects of nitrification, absorption and fixation in farmland red soil. Some of the NO3(-)-N concentrations at 40-60 cm soil depth exceed the safe drinking level of 10 mg L(-1), especially when the ADN flux is beyond 60 kg ha(-1) N. These features are critical for understanding the ADN agro-ecological effects, and for future assessment of ecological critical loads of ADN in red soil farmlands.

Effects of Substituting Synthetic Fertilizer with Organic Materials on Soil Organic Carbon Sequestration and Aggregate Size Distribution in Red Soil in South China

A metagenomic library consisting of 3,024 bacterial artificial chromosome clones was prepared in Escherichia coli DH10B with high-molecular-weight DNA extracted from red soil in South China. A novel cellulase gene with an open reading frame of 1,332 bp, cel5G, encoding an endo-β-1,4-glucanase was cloned using an activity-based screen. The deduced enzyme, Cel5G, belongs to the glycosyl hydrolase family 5 and shares <39% identity with endoglucanases in the GenBank database. cel5G was expressed in E. coli BL21, and the recombinant enzyme Cel5G was purified to homogeneity for enzymatic analysis. Cel5G hydrolyzed a wide range of β-1,4-, β-1,3/β-1,4-, or β-1,3/β-1,6-linked polysaccharides, amorphous cellulose, filter paper, and microcrystalline cellulose. Its highest activity was in 50 mM citrate buffer, pH 4.8, at 50°C. Cel5G is stable over a wide range of pH values (from 2.0 to 10.6) and is thermally stable under 60°C. It is highly tolerant and active in high salt concentrations and is stable in the presence of pepsin and pancreatin. The K (m) and V (max) values of Cel5G for carboxymethyl cellulose are 19.92 mg/ml and 1,941 μmol min(-1) mg(-1), respectively. These characteristics indicate that Cel5G has potential for industrial use.

Alteration of soil bacterial interaction networks driven by different long-term fertilization management practices in the red soil of South China

A laboratory experiment was performed to examine the impact of simulated acid rain (SAR) on nutrient leaching, microbial biomass, and microbial activities in a lateritic red soil in South China. The soil column leaching experiment was conducted over a 60-day period with the following six SAR pH treatments (levels): 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 and one control treatment (pH = 7). Compared with the control treatment, the concentrations of soil organic matter, total nitrogen, total phosphorus, total potassium, soil microbial biomass carbon (MBC), soil microbial biomass nitrogen (MBN), and average well color density (AWCD) in the Ecoplates were all significantly decreased by leaching with SAR at different pH levels. The decrease in MBC and MBN indicated that acid rain reduced the soil microbial population, while the decrease in AWCD revealed that acid rain had a negative effect on soil bacterial metabolic function. Soil basal respiration increased gradually from pH 4.0 to 7.0 but decreased dramatically from pH 2.5 to 3.0. The decrease in soil nutrient was the major reason for the change of soil microbial functions. A principal component analysis showed that the major carbon sources used by the bacteria were carbohydrates and carboxylic acids.

Considering the problems of high tillage resistance and high energy consumption in existing subsoiling shovels, the contour-fitting curve characteristics of the front paw toes of mole crickets were applied to the structural design of subsoiling shovels using bionic principles. Combined with the structure of an existing subsoiling shovel, three types of bionic subsoiling shovels were designed using bionic principles, aiming to reduce tillage resistance and energy consumption. In order to investigate their tillage effect, the microparameters of the red soil in South China were calibrated using EDEM 2020, and a corresponding discrete element soil model was established. The simulation conducted on the subsoiling process using both common and bionic subsoiling shovels, and the disturbance of the red soil by common and bionic subsoiling shovels, as well as the tillage resistance and kinetic energy experienced by subsoiling shovels, were studied. The results demonstrated that, compared with the common subsoiling shovel, the bionic subsoiling shovel 1 experienced a 5.31% reduction in tillage force, with a 4.01% reduction in tillage force at the shovel tip, a 7.15% reduction in tillage force at the shovel handle, and a 6.33% reduction in energy consumption. The bionic subsoiling shovel 2 experienced a 9.25% reduction in tillage force, with an 11.43% reduction in tillage force at the tip, a 5.49% reduction in tillage force at the handle, and a 10.58% reduction in energy consumption. The bionic subsoiling shovel 3 experienced a 6.55% reduction in tillage force, with a 5.87% reduction in tillage force at the tip and a 7.72% reduction in tillage force at the handle. Further verification has shown that the bionic subsoiling shovel has better resistance reduction and energy reduction effects.