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Drought is a significant abiotic stress that alters plant physiology and ultimately affects crop productivity. Among essential plant nutrients, potassium (K) is known to mitigate the deleterious effect of drought on plant growth. If so, K addition or inoculation of potassium solubilizing microorganisms (KSMs) that are tolerant to drought should promote plant growth during water stress. Therefore, in this study, K solubilizing Aspergillus violaceofuscus and Bacillus licheniformis, isolated from saxicolous environments, were tested for their capacity to tolerate drought using different molecular weights (~4000, 6000, and 8000 Da), and concentrations (0, 250, 500, 750, 1000, and 1250 mg/L) of polyethylene glycol (PEG) under in vitro conditions. The results showed that high concentrations (750 and 1000 mg/L) of PEG with different molecular weight considerably improved bacterial cell numbers/fungal biomass and catalase (CAT) and proline activities. Moreover, the ability of KSMs alone or in combination to impart drought tolerance and promote plant growth in the presence and absence of mica (9.3% K2O) supplementation was tested in Alfisol and Vertisol soil types under greenhouse conditions. The results revealed that the tomato plants inoculated with KSMs individually or dually with/without mica improved the physiological and morphological traits of the tomato plants under drought. Generally, tomato plants co-inoculated with KSMs and supplemented with mica were taller (2.62 and 3.38-fold) and had more leaf area (2.03 and 1.98-fold), total root length (3.26 and 8.86-fold), shoot biomass (3.87 and 3.93-fold), root biomass (9.00 and 7.24-fold), shoot K content (3.08 and 3.62-fold), root K content (3.39 and 2.03-fold), relative water content (1.51 and 1.27-fold), CAT activity (2.11 and 2.14-fold), proline content (3.41 and 3.28-fold), and total chlorophyll content (1.81 and 1.90-fold), in unsterilized Alfisol and Vertisol soil types, respectively, than uninoculated ones. Dual inoculation of the KSMs along with mica amendment, also improved the endorrhizal symbiosis of tomato plants more than their individual inoculation or application in both soil types. These findings imply that the A. violaceofuscus and B. licheniformis isolates are promising as novel bioinoculants for improving crop growth in water-stressed and rainfed areas of the tropics in the future.

Rice productivity in acid sulfate soils are frequently limited due primarily to strong acidity, low phosphorus (P) availability and metal toxicity. A recent study has documented that the use of sodium bentonite (NaB), non-hazardous material uses in natural gas pipeline construction, could be a promising soil amendment for mitigating major concerns experiencing in acid sulfate soils. Here we examined the effects of NaB and dolomite (DL) on dynamics in dissolved contents of both nutrient and associated elements in an acid sulfate soil and rice yield from paddy field in natural gas pipeline Rights-of-Way. The results demonstrated that the NaB and DL utilization significantly alleviated soil acidity and metal (Al, Fe, and Mn) toxicity (α = 0.05). Both soil amendments also significantly improved readily available P. Nonetheless, the soil NaB incorporation did elevate soluble sodium and did plummet soluble K, Ca, and Mg. Therefore, appropriate ratios and amounts of the K, Ca, and Mg along with N fertilizers are indisputable needed to maintain the nutrient balance when applying NaB as a soil amendment. Our finding implies that combined use of NaB and DL are suggested to soil amendment and could alleviate nutrient imbalance as compared to the sole NaB utilization.