Abstract:

Appropriate reduction of nitrogen fertilization is an important way to deal with serious nitrogen loss and low fertilizer-nitrogen use efficiency in field ecosystem in China.However,it is unclear whether reducing nitrogen fertilizer input can maintain the yield of densely planted cotton after oil.Taking the post oil direct seeding cotton field in Dongting Lake area as the research object,compare the yield,photosynthetic characteristics of main stems and leaves,nitrogen use efficiency and other differential characteristics of cotton under two-year nitrogen fertilizer reduction and deep application,and analyze the feasibility of nitrogen fertilizer reduction and deep application,so as to provide a scientific basis for the formulation of fertilization management measures in direct seeding cotton fields after oiling.From 2018 to 2019,the deep application test of nitrogen fertilizer reduction was carried out in Maowan base of Hunan Institute of Cotton Science,Changde City,Hunan Province.Five nitrogen fertilizer application treatments(0,90,180,270,360 kg/ha)and two deep application treatments(5,15 cm)were set up.Samples were taken during the main growth period of cotton to measure the net photosynthetic rate,soluble sugar and starch content of functional leaves of main stems,the aboveground plant biomass and NPK content of each part.To study the effects of deep application of nitrogen fertilizer reduction on the yield,photosynthetic characteristics,aboveground plant biomass,NPK accumulation and distribution of densely planted cotton after oil.With the increase of N-fertilizer application rate,the Pn,soluble sugar and starch content of functional leaves of cotton main stem and the accumulation of NPK in cotton plant increased first and then decreased in the middle and late stages,all of which were the highest at 270 kg/ha;the apparent utilization rate of nitrogen fertilizer,agronomic utilization rate,partial productivity and production efficiency are opposite;in addition,under the same nitrogen application rate,the indicators of deep 15 cm treatment were higher than that of shallow 5 cm treatment.Reasonably reducing the amount of nitrogen fertilizer combined with deep application treatment is conducive to the accumulation and balance of biomass in vegetative and reproductive organs of cotton plants,as well as the absorption and distribution of nitrogen,phosphorus and potassium,so as to promote the improvement of yield and quality.Based on the dense planting mode after oiling,it is recommended that the amount of nitrogen applied to cotton should be 180-224 kg/ha and the depth of fertilization should be 15 cm.

Key words: Cotton, Nitrogen fertilizer, Fertilization depth, Photosynthetic characteristics, Yield, Nitrogen utilization efficiency