Effect of time, form and concentration of nitrogen application on Chinese cabbage tipburn.
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概要
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In summer Chinese cabbage cultivation, both tipburn and internal rot are very serious problem which are generally thought to be caused by calcium deficiencies attributable to a variety of environmental, physiological or nutritional factor.<BR>It was confirmed by a series of the sand culture experiments at AVRDC, that NH<SUB>4</SUB>-N toxicity, rather than calcium deficiency was a more direct cause of tipburn in summer grown Chinese cabbage. Calcium deficiency, which was considered a cause of tipburn, was brought about by water stress due to root damage by NH<SUB>4</SUB>-N toxicity. Therefore, under the following conditions tipburn and internal rot become a serious hazard in the tropics: 1) Poorly drained soils, 2) Soils with a high water table, 3) After heavy rain, especially at head formation initiation.<BR>The head formation stage is the most sensitive period to tipburn; hence, NH<SUB>4</SUB>-N should be avoided at this stage. An optimum ratio of ammonia to nitrate is necessary to get maximum yield. At the early stage, NH<SUB>4</SUB>-4 is superier to NO<SUB>3</SUB>-N in accelerating plant growth, thereby, NH<SUB>4</SUB>-N application is preferable; however, the ratio of NH<SUB>4</SUB>N to NO<SUB>3</SUB>-N should be gradually reduced until one week before head formation, after which, NO<SUB>3</SUB>-N must be the sole source of nitrogen.<BR>To minimize both tipburn and internal rot in Chinese cabbage, management which eliminates excess soil moisture rapidly and decreases nitrogen supply to plants are recommended for its summer cultivation.
- 日本熱帯農業学会の論文
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