Abstract: Flower and boll stage is a key period for lint yield and fiber quality. Studying the spatial and temporal variability of available nutrient in cotton field at flower and boll stage can provide theoretical base for exploring the physiological measurements to improve lint yield and fiber quality. The field experiments were carried out in 2004 at application levels of 0, 120, 240, 360, and 480 kg N ha^-1(marked N0, N1, N2, N3, N4 respectively), 185 kg P ha^-1 and 118 kg K ha^-1 in Anyang and Nanjing, the typical representatives for ecological regions in Yellow River Valley and the middle lower reaches of Yangtze River Valley in China. The results indicated that, in the process of growth, the content of soil alkali-hydrolyzable nitrogen in 0–60 cm soil layers of N0 treatment presented the trend of decreasing firstly and increasing then. While that of other treatments decreased firstly, increased after topdressing, decreased again, and increased after the beginning of boll opening. Soil available phosphorus and available potassium in 0–60 cm soil layers at two experimental locations presented the similar trends of decreasing firstly and increasing then. Soil available nutrient in 0–60 cm soil layers decreased with the deepening of the layer. Soil alkali-hydrolyzable nitrogen and available phosphorus in the same soil layer of N1, N2, N3, and N4 treatments in Nanjing presented the similar decreasing as the horizontal distance to cotton plant increased, and in N0 treatment, there was no significant variation in alkali-hydrolyzable nitrogen and available phosphorus contents. The spatial and temporal variability for soil alkali-hydrolyzable nitrogen was more significant in Nanjing than in Anyang. While for soil available phosphorus, it was more significant in Anyang than in Nanjing. Soil available potassium in 0–60 cm soil layers in Nanjing and in 20–60 cm soil layers in Anyang presented the similar decreasing with the increasing of horizontal distance to cotton plant, while that in 0–20 cm soil layers in Anyang increasing. As a result, at the nitrogen application level of 360 kg ha^-1 for Anyang and 240 kg ha^-1 for Nanjing, yield components were the relatively optimal, yield was the maximum and the fiber quality of length and strength was better. So, in order to increase lint yield and fiber quality, different ecological regions should follow the spatial and temporal variability of soil available nutrient in cotton field at flower and boll stage to confirm the optimal fertilizer level.

Key words: Flower and boll stage, Available nutrient, Spatial and temporal variability, Lint yield, Fiber quality