关键词: 棉花; 壳聚糖; 黄腐酸; 海藻酸; 氮素利用率

Abstract:

[Objective] Excessive application of nitrogen fertilizer is a common phenomenon in cotton production. The effects of nitrogen reduction combined with biostimulants on cotton growth and nitrogen utilization were studied to provide theoretical basis for optimal nitrogen management, reducing nitrogen use and improving nitrogen efficiency. [Methods] In this study, field experiments were carried out in two seasons, with a series of nitrogen levels combined with various biostimuli applied in the experimental field. Nitrogen application setup includes the standard quantity of nitrogen fertilizer (360 kg·hm^-2, N₁), the reduction of 20% (288 kg·hm^-2, N_0.8) and the reduction of 40% (216 kg·hm^-2, N_0.6). The biostimulant application setup includes no stimulant (0 g·kg^-1, S₀), fulvic acid (0.12 g·kg^-1, F), chitosan (0.1 g·kg^-1, C), alginic acid (0.24 g·kg^-1, A). Cotton dry matter accumulation, chlorophyll content, soluble protein content, root morphology, cotton yield, total nitrogen uptake and utilization efficiency in plants among the above-mentioned conditions were analyzed. [Results] Appropriate amount of nitrogen reduction combined with chitosan, fulvic acid and alginic acid promotes the growth of cotton, increases the yield and the use efficiency of nitrogen fertilizer. Cotton plant height, dry weight, chlorophyll content, soluble protein content, yield, and total nitrogen uptake reached the maximum in the 40% nitrogen reduction plus chitosan treatment. During the initial flowering stage to peak boll-setting stage, the soluble protein content in bolls from 40% nitrogen reduction plus chitosan treatment was 41.41% higher than the control, and the number of cotton buds and bolls, the single boll weight and the yield of seed cotton was 7.85, 6.79 and 46.47 g, which were significantly increased by 19.69%, 23.39%, and 37.92% compared with the control. The 40% reduction in nitrogen combined with chitosan had the largest total nitrogen uptake during the cotton harvest period, which was 11.06 g per plant, 142.37% higher than the control. The partial factor productivity of nitrogen fertilizer, the agronomic efficiency of nitrogen, and the recovery efficiency of applied nitrogen were increased by 37.93%, 247.87%, 77.53% compared with the control. Nitrogen reduction by 20% combined with fulvic acid treatment had the greatest improvement in root morphology. The root surface area, root length, root volume, average diameter, root tip number, and branch number increased by 63.56%, 28.96%, 305.74%, 103.22%, 100.16%, 105.69% than the control, respectively. The combined application of 20% nitrogen reduction plus alginic acid significantly increased cotton boll weight and boll number, and improved seed cotton yield and nitrogen use efficiency compared with N_0.8S₀ fertilizer application. [Conclusions] Appropriate nitrogen reduction combined with chitosan, fulvic acid and alginic acid can promote cotton plant height and chlorophyll content, optimize the accumulation of dry matter in different organs and maximize the transportation of soluble protein from vegetative organs to buds and bolls, promote nitrogen fertilizer accumulation at maturation stage, and increase boll weight and the number of bolls, and eventually increase yield and nitrogen fertilizer use efficiency.

Key words: cotton; chitin; humic acid; alginic acid; nitrogen utilization