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Experiments were conducted for thirty representative surface and subsurface soils collected from different physiographic units and moisture regimes in southern Iran to assess factors affecting K pools distribution and potassium release rate, using two organic and inorganic extractants and their association to mineralogy and some physical and chemical properties in calcareous soils. Mineralogical analysis indicated that illite, smectite, chlorite and palygorskite were the main clay minerals in the studied soils. The highest content of illite and smectite was observed in the piedmont plain (P.P) units, whereas that of smectite in Lowland (L.L) unit was higher than in soils of alluvial fans (A.F). It seems that the P.P unit which is in more stable landform position contains larger amounts of all K compounds due to higher clay and illite contents. The exchangeable, non-exchangeable (NEK), structural, and total potassium were found to be significantly and positively correlated to the clay content, cation exchange capacity, and the contents of illite, smectite, and vermiculite minerals, while a negative correlation as observed between the mentioned K forms and the calcium carbonate (CaCO3) content. The cumulative rate of K release to 0.01 M CaCl2 and oxalic acid was examined for a period of 1200 h, ranging within 104–286 and 87–233 mg kg–1 for the surface soil and 98–241 and 82–211 mg kg–1 for the subsurface soil samples, respectively. The percentage of non-exchangeable K released varied greatly between the different units and moisture regimes. Higher values of NEK release were observed for P.P followed by A.F, and L.L units. Considering the obtained values of the highest amount of potassium compounds as well as the release values in the piedmont plain physiographic unit and the xeric moisture regime as well as the Alfisols, the results confirm that in addition to physicochemical and mineralogical properties, physiographic units and soil moisture regimes also play a key role in nature and in spatial distribution of different forms of potassium. [ABSTRACT FROM AUTHOR]

The potassium supplying capacity of the waste mica powder (WMP) was evaluated through chemical and biological means. Four different size fractions of the WMP were studied in laboratory by different chemical extractants. At the same time, experiment of the plant growth was conducted in pot using K-deficient soil. The K release from the WMP by different extractants followed an increasing trend with an increase in the fineness of the particles. The highest K release was recorded by boiling 1 M HNO3 (376.4–1726.4 mg kg−1) followed by 1 M ammonium acetate (33.5–226.5 mg kg−1), 0.01 M citric acid (31.6–158.3 mg kg−1) and water (12.0–112.0 mg kg−1) irrespective of the various size fractions. Significantly, higher cumulative K release from the WMP in successive extraction was recorded with 1 M boiling HNO3 that predicts its slow-release property. The K release by different extractants was correlated significantly and positively with the biomass yield and K uptake by plants. 1 M boiling HNO3 extractable K showed higher correlation values with the biomass yield and K uptake. Therefore, it suggests that the extractant might be a better indicator of K supplying capacity of the WMP. The plant intervention was able to extract 32.8% of total K from the WMP simultaneously improving the exchangeable and non-exchangeable K pool in soil. These above-mentioned results conclude that plants can get access to a significant amount of K from the WMP and it could be an effective source of K in highly weathered tropical soils under K deficiency. [ABSTRACT FROM AUTHOR]

Aims: In Alfisols, potassium (K) deficiency limits productivity, as these soils are poor in K-bearing minerals such as mica. As nutrient management practices greatly influence K nutrition of crops especially in the longer term, we evaluated the effects of 27 (1978-2004) years of cropping fingermillet ( Eleusine coracana G.) under different manure and mineral fertilizer treatments on K release, balance and yield sustainability on K deficient Alfisols in the semi-arid tropical region of southern India. Methods: Fingermillet (variety: PR-202) was grown each year under rainfed conditions with 5 different nutrient management treatments: control (no amendment), 10 Mg ha farm yard manure (FYM), 10 Mg ha FYM +50 % NPK, 10 Mg ha FYM +100 % NPK and 100 % NPK. Potassium release characteristics in the soil profile were determined using 1 N boiling HNO (strong extracting solution), 0.01 M HCl (medium extracting solution) and 0.01 M CaCl (mild extracting solution). Results: Continuous cropping of Alfisols for 27 years resulted in a decrease in K supplying capacity due to soil K depletion through crop K uptake. In soils without K addition, inherent soil supply could not meet the K requirement of fingermillet; thus, a negative K balance following 27 years of cropping affected K nutrition of the crop in all the treatments. As a result, the highest sustainable yield index (SYI) was observed using an integrated nutrient supply (combined application of nutrients from organic and inorganic sources), and the lowest index was obtained without K additions. Conclusion: For balanced nutrient management in cereal production systems, K nutrition needs urgent attention in the K deficient Alfisol region of southern India. Addition of any amount of organic manures available at field level offers an alternative strategy for maintaining soil K fertility to improve and sustain crop productivity. [ABSTRACT FROM AUTHOR]

The influence of hypoosmotic shock on the solute content of growing Escherichia coli K-12 cells was investigated at 37°C. Within 20 s after the shock the cells had released most of their osmolytes K, glutamate and trehalose. This release was specific and not due to rupture of the cell membrane, since under these conditions i) the cells neither lost protein nor ATP, ii)[C]-labeled sucrose did not enter the cytoplasm from the periplasm, and iii) except for their glutamate and aspartate level, which decreased, the amino acid pool of alanine, lysine and arginine of the cells remained approximately constant. Within a minute after the shock the cells started to reaccumulate parts of their previously released glutamate, aspartate and K, but not trehalose and resumed growth within 10 min after the shock. Experiments with K-transport mutants showed that none of the genetically-identified K transport systems is involved in the K-release process. Reaccumulation of K took place via the uptake systems TrkG and TrkH. The possibility is discussed that the exit of solutes after hypoosmotic shock occurs via several stretch-activated channels, which each allow the release of a specific osmolyte. [ABSTRACT FROM AUTHOR]

The autonomic receptors of the rat sublingual gland were characterized by radioligand binding and by specific functional responses involving the release of K and the generation of cyclic AMP in vitro. Both muscarinic cholinergic and alpha-adrenergic receptors were present in moderately high density in the sublingual gland, as judged by the binding of the specific radioligands H-QNB and H-clonidine ( B in pmol/g tissue=18.4±2.4 and 9.9±1.3, respectively). By contrast, although alpha and beta-adrenergic receptors were detected, they were not present in large numbers. The B (pmol/g tissue) for the binding of H-prazosin and H-DHA were, respectively, 3.2±0.6 and 3.6±0.4. Stimulation of muscarinic cholinergic receptors with carbamylcholine (2×10 M) caused a net release of K from sublingual slices incubated in an enriched, oxygenated Krebs Ringer bicarbonate medium of 35±7% after 10 min of incubation. Norepinephrine, phenylephrine, clonidine and isoproterenol did not induced K release from the slice preparation, but actually reduced the basal or unstimulated release of K. As in the submandibular and parotid glands, the release of K from sublingual slices had two components, a passive efflux and an active uptake which depended on the activation of an ouabain-sensitive Na, K ATPase. The release of K was also dependent on the presence of Ca (2.7 mM) in the incubation medium. Stimulation of beta-adrenergic receptors with isoproterenol (10 M) caused a 9-fold increase in the content of glandular cyclic AMP (from 4.0±0.6 to 36.0±2 pmol/mg/10 min). A similar increase was observed with norepinephrine (10 M) in the presence of phentolamine (10 M). Clonidine at concentrations of 10 and 10 M reduced the cyclic AMP content to below basal levels. The rat sublingual gland has functional cholinergic receptors and can release K in vitro in the presence of cholinergic agents. In contrast to the other major salivary glands, it has a low density of alpha-adrenergic receptors and fails to release K upon stimulation with alpha-agonists. The functional significance of a low density of beta-adrenergic receptors is still unclear, although there is a definite glandular cyclic AMP response upon stimulation with isoproterenol. Abundant alpha-adrenergic receptors in the sublingual gland are apparently negatively coupled to adenylate cyclase. [ABSTRACT FROM AUTHOR]

Amylase and K release were measured in slices obtained from innervated and sympathetically denervated rat parotid glands. Amylase release induced by noradrenaline was found to be increased after chronic denervation. The postjunctional component of supersensitivity to noradrenaline was evidenced by an increase in the maximal response to this agonist. The maximal response of denervated glands was blocked by propranolol 10 M. On the other hand, chronic denervation did not modify the α-adrenoceptor-mediated response, K release, either in the presence or in the absence of ouabain. It is concluded that, after sympathetic denervation, postjunctional supersensitivity develops for the β-adrenoceptor-mediated but not for the α-adrenoceptors-mediated effects of noradrenaline. [ABSTRACT FROM AUTHOR]