| Soil culture, pot experiment and field experiment were conducted to study the characteristics of soil exchangeable potassium, calcium and magnesium content, the effect of combined application of potassium, calcium and magnesium fertilizer on growth, physiological process and quality of flue-cured tobacco, and suitable ratio of potassium, calcium and magnesium in flue-cured tobacco plant on the condition of the climate and soil in fujian.Soil culture results showed soil exchangeable potassium, calcium and magnesium content had increased significantly after different combined applications of potassium, calcium and magnesium fertilizer were applied. Soil exchangeable potassium and magnesium content raised at first, and it got down following time gone, as well as exchangeable calcium content was adverse to exchangeable potassium and magnesium contents. After potassium fertilizer was applied, soil exchangeable potassium increased obviously, as well as soil exchangeable magnesium decreased, which showed magnesium activities got lowlier if the concentrations of potassium in soil were added, soil exchangeable calcium also decreased with raising potassium fertilizer. After calcium fertilizer was applied, soil exchangeable calcium increased significantly whereas soil exchangeable magnesium decreased. Soil exchangeable potassium was higher than that of CK treatment at first, which was lower than that of CK treatment after 90 days yet in soil culture. It was found that soil exchangeable magnesium was higher apparently than that of CK treatment, and soil exchangeable potassium was higher than that of CK treatment too, whereas soil exchangeable calcium decreased a litter after magnesium fertilizer wasapplied.Pot experiment was carried out to study the effect of combined application fertilizer of potassium, calcium and magnesium on physiological metabolism. The results showed K2Ca1Mg (f) treatment ratio of chla/chlb was high, the content of malondialdehyde (MDA) and activities of superroxide dismutase (SOD), peroxidase (POD) and catalase (CAT) was still low during first bloom, which indicated that suitable combined application fertilizer of potassium, calcium and magnesium kept the balance of active oxygen metabolism in flue-cured tobacco leaves, and reduced the lipid peroxide and prolonged the aging of leaves. Chlorophyll and carotene of the K3Ca2Mg (j) treatment were low, and the content of MDA increased, SOD and POD activities increased too, as long as the activity of CAT reduced, which broke the balance of active oxygen metabolism in flue-cured tobacco leaves.Potassium, calcium and magnesium are important nutrients for flue-cured tobacco .The deficiency of them will cause yield and quality to decease. Pot experiment results showed significant interaction among potassium, calcium and magnesium. The leaves uptake of others was contained with the addition of anyone of three nutrients. Different combined application fertilizer of potassium, calcium and magnesium had significant effect on the nutrients content and total uptake of nutrients. Soil exchangeable potassium, calcium and magnesium content increased greatly after potassium, calcium or magnesium fertilizer was applied .The research indicated it was gained high biomass on the condition that application ratio of potassium, calcium and magnesium was 1 : 1.05: 0.16, and the yield was 19.17 percent higher than CK treatment. Field experiment result showed yield and the ratio of high quality tobacco was increased remarkably on the condition that the ratio of potassium, calcium and magnesium in plant was 1:0.54:0.07, which werel97.2kg.acre-1 and 57.97 percent. The results of potassium, calcium and magnesium content analysedshowed the contents of potassium and calcium were normal; magnesium content was lower to normal level, which suggested it be needed to increase magnesium fertilizer. The yield and quality were not increased significantly if the addition of potassium fertilizer was beyond plant need. It was suggusted that a optimum application...
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