Feasibility assessment of bentonite drilling mud to improve the physical quality of loamy sand soil and water deficit of forest plant seedlings.

Spent drilling mud (DM), a co-product during horizontal directional drilling operations, needs proper disposal to comply with social and environmental sustainability awareness, with one option being its cost-effective reuse as a soil amendment. The possibility was investigated of DM applications to improve the physical quality of loamy sand soil. The soil was treated with increasing DM contents in a laboratory at volumetric DM-to-soil ratios of 0:100 (DM0, no DM), 25:75 (DM25), 50:50 (DM50), 75:25 (DM75), and 100:0 (DM100, no soil). The mixtures were analyzed for water retention, available water capacity, water storage capacity, S-index, soil aggregate stability (SAS), and chemical quality based on pH, effective electrical conductivity (ECe), sodium adsorption ratio (SAR), and exchangeable sodium percentage (ESP). The optimal ratio of DM and the control (DM0) in the batch experiment were selected for application to three species of forest plant seedlings in the field. The results showed that DM positively influenced soil physical qualities. The water retention increased (from 10 to 67%) with increasing DM, but the most suitable ratio was DM25, considering its water storage capacity deviated the least (1.4%) from the optimal value. DM25 also produced the highest S-index (0.081). The SAR data increased with the drilling mud application rate (1.1 to 10.9). However, the DM25 pH remained at 7.7, with an ECe of 2.5 dS m-1, a SAR of 7.0, and an ESP of 9.2, which were still favorable regarding soil structure, as indicated by no decrease in SAS with added drilling mud. In the field experiment, DM25 also decreased the water deficit of the three species of forest plant seedlings, suggesting a positive attribution to other relevant soil-plant systems. DM could be a feasible option to improve soil physical quality, but further long-term experiments are necessary before applying it as a soil amendment in real situations.Implications: With the demand in energy-driven economics, establishing national energy security nationwide in Thailand requires the installation capacity, transmission, and distribution pipelines. Horizontal directional drilling (HDD) operations are generally used to install underground pipelines, generating large amounts of drilling mud rich in sodium bentonite as a co-product. At present, drilling mud is becoming a more serious solid waste and has been raised in proper management. The best management practices are expected to reuse as a soil amendment, a cost-effective approach, for coarse-textured soils. Before any drilling mud application can be introduced to agriculture and the environment, we must clarify the optimal rate of drilling mud. This rate has to significantly improve soil physical quality associated with air-water capacity balance while minimizing the adverse effect of residual sodium to favor soil structure and sensitive plants.

Sulfur amendments to soil decrease inorganic arsenic accumulation in rice grain under flooded and nonflooded conditions: Insights from temporal dynamics of porewater chemistry and solid-phase arsenic solubility.

Rice cultivation under flooded conditions enhances arsenic (As) solubility and favors As accumulation in rice grain that poses an indisputable threat to human health worldwide. The reduction of sulfur may induce processes that decrease As solubility, but its impact on rice grain As species remains unresolved. Herein, we investigated the influence of sulfur (S)-containing materials, including chicken manure and elemental sulfur powder on As accumulation and speciation in rice grain as well as the dynamics of the porewater chemistry and solid-phase As solubility throughout the entire growth stage under continuous flooding and intermittent flooding conditions in pot experiments. The S amendments (200 mg S kg-1) to the soil significantly decreased inorganic As in rice grain under continuous flooding (~65% decrease) as well as under intermittent flooding (~70% decrease). The chicken manure amendment promoted sulfur reduction and enhanced dissolvable Mn, Fe, and As at an earlier growth stage. The sequential extraction results corroborated a decrease in the soluble and exchangeable As (F1) and an increase in residual As (F5) fractions in the S-amended treatments. Solubility data suggested that As adsorption onto Fe oxides was the primary mechanism controlling As solubility rather than the formation of AsFe sulfides. Porewater As, considered to represent the most bioavailable As fraction, failed to explain the grain As accumulation. The time-averaged concentration of oxalate-extractable As explained grain arsenite best, suggesting that poorly crystalline Fe oxides may be the primary dissolvable reactive phases that control As bioavailability in the soil-rice system. Our results suggest that the application of S-containing soil amendments can effectively decrease inorganic As accumulation in rice grains grown under the flooded conditions, which are most widely applied in paddy rice production.

Performances of the WEPP and WaNuLCAS models on soil erosion simulation in a tropical hillslope, Thailand.

Effective soil erosion prediction models and proper conservation practices are important tools to mitigate soil erosion in hillside agricultural areas. The Water Nutrient and Light Capture in Agroforestry Systems (WaNuLCAS) and Water Erosion Prediction Project (WEPP) models are capable tools in soil erosion simulation in the conventional and conservation cropping systems in hillslopes. We calibrated both the models in maize monocropping and simultaneously validated them in maize-chili intercropping with Leucaena hedgerow for nine rainfall events in 2010, with the aim to evaluate their performances in runoff and sediment prediction on a skeleton soil in a hillslope, Western Thailand. The results showed that the calibrated WaNuLCAS model poorly predicts runoff prediction in the validation. In contrast, the calibrated WEPP model had a better performance in runoff prediction in the validation. For sediment prediction, the calibrated WaNuLCAS model predicted sediment yield better than the calibrated WEPP model in the validation because the WEPP model shows more variability of the sediment yield in the calibration (5.84 kg m-2) than the WaNuLCAS (5.18 kg m-2). Thus, the WEPP model was more suitable for runoff prediction than sediment prediction in the monocropping system, whereas the WaNuLCAS model was better suited for sediment yield prediction than runoff prediction, especially in complex intercropping systems.