Abstract:

【Objective】 The effects of N content in soil on the physiological and biochemical indexes, amount of dry-matter accumula, tissue water content, boll load per unit leaf in cotton were studied in the field. 【Method】 The physiological characters of the leaves on stem , amount of dry-matter accumulation and tissue water content of the above-ground cotton plants, boll load per unit leaf was studied under different N levels (low level, 0 kg?hm-2, middle level, 189.50 kg?hm-2, high level, 395.0 kg?hm-2). 【Result】 The turning point from bloom to senescence is at the later full boll stage. The results showed that there was a negative correlation between nitrogen and the cotton premature senescence. Compared to mid-nitrogen and high-nitrogen treatments, under the condition of low nitrogen, the content of Chl. and dissolvable protein, photosynthetic rate, the amount of dry-matter accumulation and the activities of SOD and POD all decreased. But the content of MDA and boll load per unit leaf increased. It was concluded that cotton had a faster senescence under low nitrogen treatment. However, the efficiency of nitrogen decreased with the increase of nitrogen (from middle N level to high N level). 【Conclusion】N content in soil affects the cotton senescence remarkably. Low-nitrogen decreased the physiological characteristics of leaves, and protmoted the senescence; mid-nitrogen and high-nitrogen delay aging.

Key words: cotton, nitrogen, leaf senescence, physiological effect