[Diagnosis method of cotton water status based on infrared thermal imaging].

Canopy temperature is one of promising signals for evaluating crop water status. The infrared thermal imager can provide real-time temperature distributions over larger areas with high spatial resolution. The main factors (the observation orientation, angle and distance) controlling the accuracy of measuring canopy temperature with the infrared thermal imaging were investigated in a cotton field. Moreover, the correlation relationships between the crop water stress index (CWSI), which was observed using different methods, and soil water content (SWC), leaf water potential (LWP), and stomatal conductance (g(s)) of cotton in different water treatments were analyzed. Results indicated that the CWSI, which was measured in the opposite direction of the sun with the observation angle of 45°, was in good correlation with LWP, g(s) and SWC, indicating it was a suitable observing method of canopy temperature. The canopy temperature gradually decreased with the increasing observation distance, so the calibration was necessary for long-distance measurement. By analyzing the relationship between the temperature at the dry/wet reference surface and the canopy temperature, we developed a suitable and simplified model of CWSI for cotton in the North China Plain.

[Effects of girdling on growth, yield and water use efficiency of cotton].

An experiment with girdling applied on the main stem and fruit branch during the early or flourishing stage of flowering and boll-setting was conducted to investigate the effects of different girdling treatments on the growth, yield and water use efficiency (WUE) of cotton. The results showed that compared with the control (CK), leaf area index (LAI) of girdling treatments reduced significantly and the maximum LAI of girdled cotton occurred 5-15 days in advance. Girdling reduced the shedding rate of squares and bolls significantly, and the shedding rate of squares and bolls with girdling applied on the main stem at the flourishing stage was 15.8% lower than that of CK. In contrast with CK, the seed-cotton yield and WUE increased by 24.4% and 26.7% with girdling applied on the main stem at the flourishing stage, and increased by 13.9% and 16.7% with girdling applied on the fruit branch at the early stage, respectively. However, the girdling on the fruit branch at the flourishing stage improved the seed-cotton yield and WUE insignificantly. The seed-cotton yield with girdling on the main stem at the early stage had not significant difference and its WUE reduced slightly compared with CK. It has been concluded that the girdling applied on the main stem at the flourishing stage of flowering and boll-setting could effectively reduce the abscission rate of squares and bolls, improve yield and WUE significantly, and realize the effective unity of high production and water-saving.