Abstract:

The target of this study was to seek methods of nutrition diagnosis of cotton at different growth and development stages by chlorophyll SPAD values of upper leaves of cotton plant. The experiment was carried out to study the dynamic change of first leaf to forth leaf from top of cotton main stem during the whole growth period with two early cultivars (CCRI 36, CCRI 50) and two mid-maturing cultivars (CCRI 41, SCRC 28), at the same time the impact of different nitrogen and phosphorus fertilizer rates on chlorophyll SPAD values of the main stem function leaves of SCRC 28 were studied. The results showed that chlorophyll SPAD values of the main stem leaves of two early cultivars had same rule during the whole period, chlorophyll SPAD values of first leaf from top were lower than those of second leaf from top, second leaf from top were lower than third leaf from top, third leaf from top were lower than forth leaf from top, the same rule appeared in two mid-maturing cultivars before full-boll stage, but the order of chlorophyll SPAD values of upper four leaves was irregular after full-boll stage. The chlorophyll SPAD values of forth main stem leaf from top could be looked upon as the reference value of nutrient diagnosis before boll opening stage, difference value of chlorophyll SPAD values of first or second main stem leaf from top of early cultivars between about 10 days before boll opening stage and 10 days after boll opening stage could be looked upon as the reference value of degree of aging of cotton plant, difference value of chlorophyll SPAD values of third main stem leaf from top of mid-maturing cultivars between about 15 days before boll opening stage and 15 days after boll opening stage could be looked upon as the reference value of degree of aging of cotton plant. In the experiment, the chlorophyll SPAD values of main stem functional leaves had significant difference between the treatment with amount of net nitrogen more than 270 kg/hm2 and the treatment with no nitrogen, the treatment with much more nitrogen had more higher chlorophyll SPAD values of main stem functional leaves during boll opening stage. The treatment with amount of net phosphorus pentoxide at 120 kg/hm2 had more higher chlorophyll SPAD values of main stem functional leaves during boll opening stage, on the contrary, when amount of net phosphorus pentoxide was more than 120 kg?hm2-, chlorophyll SPAD values declined.