Abstract: It is urgent and necessary to provide the technology of economic application on fertilizers for nutrition improvement of Bt cotton and cotton production in coastal saline soil in the Yellow River Delta. The experiments were conducted with Bt cotton cultivar SCRC28 in coastal saline soil in the Yellow River Delta, Shandong province. The effects of different amounts and ratios of N, P and K, and N and P fertilizers on nutrient (N, P and K) assimilation, Na⁺ assimilation, net photosynthetic rate (P_n), dry matter accumulation and lint yield of Bt cotton were investigated in three types (low, middle and high levels of salinity) of coastal saline field. The results showed that nutrient uptake of Bt cotton in the treatments of NP, NPK especially, in low, middle and high levels of salinity field was significantly higher than that in corresponding controls. And the Na⁺ uptake of cotton in the same treatments was significantly lower than that in corresponding controls. Nutrient use efficiency in agronomy(NUEa) of cotton in the NPK treatment in low, middle and high levels of salinity field was the highest among the three treatments. NUEa of Bt cotton in the NPK treatment in low, middle and high levels of salinity field was 0.20, 1.95, and 2.07 kg lint kg^–1 N, 0.87, 8.35, and 8.71 kg lint kg^–1 P, and 0.26, 2.89, and 3.77 kg lint kg^–1 K, respectively. The coordination of N, P and K fertilizers could maintain the highest leaf area, chlorophyll content and P_n among the three treatments in low, middle and high levels of salinity field, respectively. The biomass yield and lint yield of Bt cotton in the NPK treatment in low, middle and high levels of salinity field were also the highest among the three treatments, respectively. The lint yield in the NPK treatments in low, middle and high levels of salinity field was 2.53%, 28.67% and 30.47% higher, respectively, than that in corresponding controls. And the fertilization effects in middle and high levels of salinity field were obviously better than those in low level of salinity field. Further analysis indicated, rational fertilizer application, according to the classification of soil salinity, was an effective way to alleviate nutrition obstacles of saline soil, improve cotton nutrition, and enhance the NUEa and cotton yield in coastal saline fields.

Key words: Bt cotton, Saline soil, N,P and K fertilizer, NUEa, Fertilization effects