Effects of nitrogen application on growth and nitrogen accumulation of cotton under shading condition

【Objectives】 Late maturation is often happened in cotton intercropped with fruit, which causes lower pre-frost lint percentage, the yield is declined seriously. Reasonable nitrogen fertilizer topdressing could regulate and control the growing process of cotton, optimize accumulation and distribution of biomass and nitrogen in organs. The study will provide theory basis for reasonable nitrogen application for the intercropping cotton. 【Methods】 The cotton cultivar was Zhangmain 49, the feild experiment was performed with split plot design. The main areas were 50% shading (S50) and not shading (CK). The split areas were N1 (earlier topdressing), N2 (normal topdressing) and N3 (more proportion of earlier topdressed nitrogen than N1). Total nitrogen was 320 kg/hm2, half of them was topdressed with irrigation. The details of topdrossing date and amont was listed in Table 1. Effects of the nitrogen application on dynamic accumulation characteristics of biomass and nitrogen under the shading were studied.【Results】 Compared with CK, the theoretical maximum biomass and growth rates of the vegetative organs were higher, while the theoretical maximum biomass, growth rates and growth eigenvalues of reproductive organs biomass were smaller under half shadding. The rapid accumulation of total nitrogen arose 5-8 d in advance, boll number, boll weight and lint percentage were reduced significantly, lint yield was reduced by 35.61% in average under the shading of 50%. Under the 50% shading, the start and finish of the rapid growth rates of the vegetative and reproductive organs under N1 were ahead, and the theoretical maximum biomass of the reproductive organs were in order of N1N2N3. The theoretical maximum nitrogen accumulation, the lasting days of rapid nitrogen accumulation and growth eigenvalues are the largest in N1, which was bonefited to the net absorption, the net transfer of nitrogen and contribution to the fiber nitrogen for vegetative organs, and the lint yield is higher than those of N2 and N3 by 18.90% and 29.07%. Under CK, the maximum growth rates and growth eigenvalues of aboveground vegetative organs biomass of N2 are the largest, and the theoretical maximum of nitrogen accumulation, the lasting days of the rapid nitrogen accumulation and growth eigenvalues were the largest, too. Boll number and boll weight were the highest, and the lint yield is 13.03% and 23.67% higher than those of N1and N3. 【Conclusions】 In condition of 50% shading, the ealier nitrogen topdressing (N1), namely, beginning at the full budding stage (in the middle and last ten days of June), ending before the full boll stage (in the first ten days of August), could improve the eigenvalues of the rapid growth period under the shading, increase cotton biomass and nitrogen accumulation significantly, be helpful to net nitrogen absorption, net transfer and contribution to the cotton fiber in vegetative organs, and increase boll number per plant, boll weight and yield finally.