Fluorine is unique chemical element which occurs naturally, but is not an essential nutrient for plants. Fluoride toxicity can arise due to excessive fluoride intake from a variety of natural or manmade sources. Fluoride is phytotoxic to most plants. Plants which are sensitive for fluorine exposure even low concentrations of fluorine can cause leave damage and a decline in growth. All vegetation contains some fluoride absorbed from soil and water. The highest levels of F in field-grown vegetables are found up to 40 mg kg-1 fresh weight although fluoride is relatively immobile and is not easily leached in soil because most of the fluoride was not readily soluble or exchangeable. Also, high concentrations of fluoride primarily associated with the soil colloid or clay fraction can increase fluoride levels in soil solution, increasing uptake via the plant root. In soils more than 90 percent of the natural fluoride ranging from 20 to 1,000 g g-1 is insoluble, or tightly bound to soil particles. The excess accumulation of fluorides in vegetation leads to visible leaf injury, damage to fruits, changes in the yield. The amount of fluoride taken up by plants depending on the type of plant, the nature of the soil, and the amount and form of fluoride in the soil should be controlled. Conclusively, fluoride is possible and long-term pollution effects on plant growth through accumulation of the fluoride retained in the soil.
There are increasing social pressures on the agricultural use of salt-affected reclaimed tideland (RTL) for the cultivation of other crops except for rice. Crop suitability for RTL has conventionally been evaluated using soil salinity alone without consideration of soil texture and water salinity. In this study, the suitability of 10 crops for 12 RTLs under national government's management was evaluated using soil and water salinity as well as soil texture. The crops include barley (both cereal and forage) (hordeum vulgare), wheat (triticum eastivum), paddy rice (oryza sativa), maize (forage) (zea mays), beet (beta vulgaris), celery (apium graveolens), spinach (spinacia oleracea), broccoli (brassica oleracea var. italic), and tomato (solanum lycopersicum). The results showed that barley and wheat are most suitable winter crops for all RTLs and beet, celery, and maize are more suitable than others as summer crops. The suitability of rice, which is widely cultivated in all RTLs, was not as high as expected in some RTLs, suggesting that it may be possible to consider other crops as alternative summer crops to rice. By using not only soil salinity but also soil texture and water salinity as parameters for crop suitability evaluation, it was possible to recommend suitable crops for each RTL of which soil texture and soil and water salinity differ.
Bacillus subtilis SA-15 is a plant growth-promoting bacterium isolated from non-farming soil. We aimed to identify lipopeptides produced by B. subtilis SA-15 and evaluate the control efficacy of B. subtilis SA-15 against large patch disease caused by Rhizoctonia solani AG 2-2 (IV) in zoysiagrass (Zoysia japonica). Bacillus subtilis SA-15 inhibited mycelial growth of R. solani AG 2-2 (IV) in vitro and produced fengycin A and dehydroxyfengycin A, which are antifungal compounds. Fengycin A and deghydroxyfengycin A inhibited R. solani mycelial growth by 30.4 and 63.2%, respectively. We formulated B. subtilis SA-15 into a wettable powder and determined its control efficiency against large patch in a field trial. The control efficacy was 51.2–92.0%. Moreover, when B. subtilis SA-15 powder was applied together with half the regular dose of the fungicide pecycuron, the control efficacy was 88.5–100.0%. These results indicate that B. subtilis SA-15 can be used to control soil-borne diseases, including large patch caused by R. solani, because of lipopeptide production. The use of this bacterium can also reduce the amount of fungicide needed, providing an eco-friendly management option for turfgrass.
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