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Fluid Journal : Fluid Journal 2002-2004
1 Fluid Journal Winter 2002 Summary: Summary: Summary: Summary: Summary: Calcium availability is es- sential in the biochemistry of plants and, as we are learning, in the nitrogen fertilizer efficiency of surface-applied urea. We should not confuse the role of important soil amendments such as lime or gypsum with the need of soluble cal- cium by high-value crops. Both are extremely important in soil fertility and plant nutrition and complement each other. Calcium fertilization of many crops is frequently confused with lime or gyp- sum soil amendments. Many believe application of these minerals to soils sufficiently supplies the calcium re- quirement of crops. Unfortunately, the role of calcium in plant nutrition is of- ten eclipsed by interest in macronutri- ents or specific micronutrients. Many overlooked and is only considered when deficiency disorders influence the economic threshold of produce quality and value. However, we know that cal- cium 1) is a multifunctional nutrient in the physiology of crop plants and 2) in the soluble form influences availability and uptake. Nitrogen-use efficiency of urea-containing fertilizers is also in- creased with soluble calcium sources such as calcium nitrate. Classical visual symptoms in calcium deficient plants include 1) death of growing points, 2) abnormally dark green foliage, 3) premature shedding of blossoms and buds, and 4) weakened stems. Our focus in this article will primarily address the importance of calcium in cell wall structure and crop production. Calcium's function Cell wall strength and thickness are increased by calcium addition. Calcium is a critical part of the cell wall that pro- duces strong structural rigidity by form- ing cross-links within the pectin polysaccharide matrix. With rapid plant growth, the structural integrity of stems that hold flowers and fruit, as well as the quality of the fruit produced, is strongly coupled to calcium availability. Solubility helps Many fruit and tuber crops such as apple and potato have a very narrow window for calcium uptake. Ninety per- Dr. G. W. Easterwood Calcium's Role In Plant Nutrition Research shows soluble calcium fertilizer plays vital role in production of high-quality crops. cent of the calcium taken up by potato tubers or apple fruit occurs within a four- to six-week period after bloom for apple or during budding for potato. Up- take can be enhanced by applying cal- cium in the soluble form (i.e., calcium nitrate or calcium chloride, either of which is immediately available for up- take). With many rapidly growing crops, insoluble sources will not provide adequate calcium fertility. Disease reduction Many fungi and bacteria invade and infect plant tissue by producing en- zymes that dissolve the middle lamella. Enzymes responsible for dissolving the middle lamella include polyglacturonases and pectolytic en- zymes such as pectate transeliminase. Increasing tissue calcium content as- tonishingly lowers polyglacturonase and petolytic enzyme activity from times, calcium fertilization has been Table 1. Bean tissue calcium content effect on bacterial pathogen infection. Ca content Polyglacturonase Pectate Erwinia (%) activity transeliminase severity * 0.68 62 7.2 4 1.60 48 4.5 4 3.40 21 0 0 * 4 = complete decay of plants in 6 days. 0 = no symptoms The medullary tissue of the tuber contains at least 200 ppm Ca.
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