1,721,012 research outputs found
?????? ?????? ?????, ?????????? ??????? ???????????? C??????? ???????????? ???? ?????? ????????? (Assessment of the level of risk associated with mercury pollution of the northern industrial zone of the city of Pavlodar)
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Bad project evaluation and planning - the reason for the apparent poor performance of irrigation schemes
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Gypsum applications to aggregated saline sodic clay topsoils
No full textGypsum application was highly efficient as a treatment for reducing amounts of exchangeable sodium and inhibiting clay dispersion in highly structured saline-sodic clay topsoils.Phosphogypsum, applied to the surfaces of aggregates in soil columns treated with simulated rainfall, was dissolved efficiently by frequent intermittent 'rainfall'. The calcium released by dissolution displaced sodium on the exchange complex within soil aggregates ranging from 7.5 mm to 45 mm in diameter. Of the applied calcium, 64–74% was transferred to ion exchange sites; however, almost one-third of this adsorbed calcium displaced exchangeable magnesium.Comparison of three gypsum treatments, phosphogypsum, rock gypsum, and a saturated gypsum solution (representing a top dressing of highly soluble gypsum), showed that the effectiveness of calcium uptake on the exchange complex followed the order: rock gypsum < saturated solution < phosphogypsum, but differences were small.Application of phosphogypsum caused a 90% reduction in the total amount of dispersed clay released in column leachates, and decreased the maximum clay concentration in the effluents by at least 80%, when compared to soils leached without gypsum treatment.<br/
Effect of different cultural-practices upon the major diseases of dark fire-cured tobacco in Malawi
No full textPriming and discarding the bottom six leaves of dark fire-cured tobacco, increased the incidence of leaf damage caused by Alternaria longipes and Cercospora nicotianae. The stem rot Erwinia carotovora also caused more damage in primed than in unprimed tobacco. Leaving 18 leaves upon the plant as opposed to 15, decreased the incidence of A. longipes and C. nicotianae in tobacco from the top of the plant (leaves 13-15). At the recommended spacing of 0.9 0.9 m, applying a balanced fertilizer did not cause any increase in fungal damage to the leaf, but it did cause an increase in infection when applied at a spacing of 0.9 1.2 m. Decreasing plant populations and increased levels of applied fertilizer both increased the incidence of E. carotovora infection
Water pathways in higher plants II. water pathways in boots
No full textThe technique for studying the pathways of water movement described, in the first paper of this series has been applied to the transpiration stream in the roots of higher plants. Free space is confined to the cell walls except in flooded tissue where intercellular spaces are also included. Errors involved in free-space estimates are discussed and free-space volumes of 5.4 per cent have been obtained for wheat root cortex and 4.1 per cent for carrot xylem parenchyma. The main water-absorbing regions of roots begin immediately behind the elongating zone, where the first xylem elements are fully differentiated, and end when the endodermis undergoes secondary wall development. In the cortex the transpiration stream is located mainly in the cell wall. Calculations indicate that the symplastic pathway is of only minor importance in transpiring plants. At the endodermis the free-space pathway is blocked by the Casparian strip and all water and solute entering the stele must pass through the lumen of the endodermal cells. The permeability of individual endodermal cells varies considerably both between cells of the same species and between those of different species. Once inside the endodermis, the transpiration stream returns to the cell-wall pathway until it reaches the xylem vessels where it enters the lumen of the mature xylem elements
Development of an empirical-statistical hydrological model relating climate and flows. (In Portuguese)
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