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Greenhouse experiments with tomato were conducted in the years 2004-2006. The aim was to study the effect of nutrient solution pH on the availability of phosphorus in soilless culture of tomato. Tomato plants were grown on mats made of shredded rye straw, and on slabs of peat and rockwool. The plants were fertilized with a standard nutrient solution of different pH: 4.5, 5.0, 5.5, 6.0 and 6.5. Such different pH levels of the nutrient solution used in soilless culture modified the pH of the root growth zone. This effect was more evident in rockwool than in the organic media (especially straw). The phosphorus content in the root zone was closely associated with the pH value of the supplied nutrient solution and the kind of growing medium. Considerably lower concentrations of phosphorus were recorded in the organic media (straw, peat) than in rockwool. As the pH level of the nutrient solution increased, so did the pH of the root zone, whereas the amount of available P-PO4 decreased. The course of these changes was similar in all the substrates. However, the dynamics of the changes was weaker in the organic media. With an increase in the pH of the nutrient solution, the average phosphorus content in tomato leaves decreased. The P-PO4 concentration was higher in the leaves of tomato plants growing in rockwool compared to those in the organic media. A significantly higher marketable yield was obtained from tomato plants cultivated in rockwool than in the organic media. For all the growing media, the highest yield of tomatoes was obtained after feeding the plants with the nutrient solution of pH 5.5.
Soil phosphorus (P) availability and fractions are influenced to a large extent by land use and cover changes. Inorganic P (IP) and organic P (OP) fractions in surface soils (0–20 cm) under typical vegetation types, including subalpine coniferous forests, alpine shrubs, and alpine shrub-meadows, near the alpine timberline of the eastern Tibetan Plateau of China, were measured by a modified Hedley fraction method. The results showed that OP is the dominant soil P fraction and the main source of available P in alpine soils near the timberline. Soil organic carbon, total nitrogen, and total P contents were higher in subalpine coniferous forests than in alpine shrubs and alpine shrub-meadows. Concentrations of soil labile P (the sums of Resin–IP, NaHCO3–IP, and NaHCO3–OP) were higher in subalpine coniferous forests than in alpine shrubs and alpine shrub-meadows, an observation that may be partially ascribed to the presence of deep litter layers generated by trees. Concentrations of soil labile and moderately organic P (NaHCO3–OP and NaOH–OP) in subalpine coniferous forests were also greater than in alpine shrubs and alpine shrub-meadows. Greater amounts of soil stable OP (extracted by concentrated HCl and cHCl–OP) were accumulated in alpine shrub-meadows compared to alpine shrubs or subalpine coniferous forests. The reduced availability of OP may be attributed mainly to increasing recalcitrant soil organic matter input in alpine shrub-meadows and alpine shrubs. Concentrations of IP associated with Ca minerals and parent materials (extracted by diluted HCl and HCl–IP, and extracted by concentrated HCl and cHCl–IP, respectively) were lower in subalpine coniferous forests, indicating that coniferous forests are more likely to use recalcitrant IP than alpine shrubs and alpine shrub-meadows. In this alpine region, land cover changes from subalpine coniferous forests to alpine shrubs and alpine shrub-meadows near the alpine timberline could decrease soil P conservation, availability, and supplementation.
The effect of inoculating single cultures of plant growth-promoting rhizobacteria (PGPR) on development of white beans seedling (Phaseolus vulgaris) was analyzed. Five PGPR were isolated from the rhizosphere of Okra plants and were assessed for abilities to solubilise phosphate and produce indole acetic acid (IAA). The phosphate solubilising index ranged from 6-10 while the concentration of IAA ranged from 17.48mg/l to 27.43mg/l. Serratia sp. produced the highest concentration of IAA (27.43mg/l) and had the highest solubilisation index (10mm). Bacillus sp. produced the least amount of IAA (17.48mg/l) while Staphylococcus sp. had the least solubilisation index (6mm). The highest percentage germination of 83.3% was observed in the seedling inoculated with Bacillus sp. The effect of PGPR on root and shoot elongation was studied hydroponically for 7 days. Significant increases (P< 0.05) in root elongation were observed.. The highest seedling root length (18.47cm) and shoot length (19.17cm) were observed with inoculation of Staphylococcus sp. and Bacillus sp. respectively. The use of these bacteria as bio-inoculants could be a sustainable practice to facilitate nutrient supply to white beans seedlings.
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