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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. [ABSTRACT FROM AUTHOR]

Electrolytes have been verified as a vital internal factor controlling soil aggregate stability (SAS). Several reports have focused on whether potassium promotes or demotes SAS and have shown contradictory results in different soils and clay mineralogy. Only a few studies have investigated such an effect on a soil-plant system, even though this information is critical for soil management practices to maintain soil structural stability. This research studied the dynamics of SAS as influenced by potassium in a soil-plant system. Corn as a test plant was grown on Haplic Acrisols (Typic Paleustults) in a greenhouse. The potassium adsorption ratio (PAR), cation ratio of structural stability (CROSS), and SAS were recorded on the day before planting (day 0), the day of planting (day 1), days 10, 20, 30, and the day of harvesting (day 55) at the tasseling stage. The corn growth, biomass, and potassium uptake were also examined. The relationship between soil and plant parameters was statistically tested. The results showed the existence of SAS dynamics caused by soil potassium change, with agreement among the responses for PAR, CROSS, and plant uptake. Within 24 h of soil treatment with potassium, the SAS move rapidly from 74% to 96%. It remained steady at 96–97% when the corn was in the vegetative stage and then fell significantly (α = 0.05) to 88% when the corn was in the tasseling stage, where the potassium uptake was maximized. The results implied that SAS is a sensitive index of soil physical quality associated with potassium, especially for tropical kaolinitic soils. [ABSTRACT FROM AUTHOR]

Physical quality and chemical fertility of lateritic soils under different types of land use were assessed and tested for their relationship. Six land-use types that have been continuously applied to similar lateritic soils (Plinthic Paleustults) were included in this study. These types of land use are (1) dry dipterocarp forest, (2) 6-year sugarcane, (3) and (4) 6-year rotating forage/sugarcane, (5) 6-year rubber plantation, and (6) 6-year mixed legume-maize cropping. The soil water retention curves and available water capacity were determined as well as S-index, a single indicator of soil physical quality, was estimated by using the parameters of the van Genuchten equation. Relevant fertility parameters were also analyzed to evaluate the fertility level. The results showed that all selected types of land use influenced the physical status and chemical fertility of lateritic soils. Dry dipterocarp forest and rubber plantation enhanced the S-index of 0.044 and 0.047, respectively, which were higher than those soils influenced by other agricultural practices (0.034–0.039). The good physical quality, as indicated by S-index, is significantly correlated (p < 0.05) with increasing available potassium and positively correlated with available phosphorus, base saturation percentage, and available water capacity. Our results imply that S-index is a useful indicator of soil physical quality associated with chemical fertility for Thai lateritic soils. [ABSTRACT FROM AUTHOR]

Improving soil aggregate stability (SAS) is important for crop production and environmental protection. Here we aim to quantify the effects of potassium (K) on SAS and to examine SAS as a function of potassium adsorption ratio (PAR) and cation ratio of soil structural stability (CROSS). The soils were treated with the incremental K and analyzed for their aggregate stability, clay dispersion, PAR, and CROSS. The influence of K on SAS, therefore, was tested statistically and fitted functionally. The results showed that K decreased clay dispersion and improved SAS. Also, SAS as a function of PAR fit an inverse exponential regression. Based on the coefficients of determination (R2) of the obtained functions, SAS can be explained by PAR with the accuracy above 94%. Increasing CROSS according to K also caused higher SAS, implying that K is considered as a flocculating inducer for kaolinitic tropical soils. [ABSTRACT FROM AUTHOR]