Effects of dicyandiamide on nitrogen loss from cucumber planting soil in intensive greenhouse under different irrigation and nitrogen conditions

【Objectives】 The traditional management mode of greenhouse vegetables is under a large number of irrigation and fertilization. This mode not only affects quality and yield of vegetables, but also causes serious waste of resources and environmental pollution. Aiming at excessive application of nitrogen fertilizer and low nitrogen fertilizer utilization rate caused by unreasonable irrigation, nitrogen loss and other waste of resources and negative effects of environmental problems in greenhouse vegetable production were studied with focusing on nitrification inhibition effect and its mechanism of dicyandiamide (DCD) to select the best water and nitrogen management program for greenhouse cucumber production. 【Methods】 A field in-situ tracking experiment was carried out to determine N2O emission, ammonia volatilization loss, inorganic nitrogen in soil and other indicators during the greenhouse cucumber dressing. N2O gas samples were collected by enclosed static box method, and gas samples was analyzed by gas chromatography with Agilent GC6820.Ammonia volatilization samples were collected by closed chamber method, added 20 mL 2% boric acid solution into evaporating dish of 50 mL, and after 24 hours, absorption of ammonia in boric acid was titrated with standard sulfuric acid. Fresh soil samples were extracted with 1.0 mol/L KCl, and analyzed for NH+4-N and NO-3-N using continuous flow analysis (TRAACS 2000) in laboratory. 【Results】 Compared with the recommended water and nitrogen treatments ofⅠandⅡ, the applications of DCD with the recommended water and nitrogen treatments ofⅠandⅡcould reduce N2O emission by 42.1% and 64.1%, while the applications increase ammonia volatilization loss by 34.3% and 40.4% respectively. Soil NO-3-N and N2O flux, NH+4-N and ammonia volatilization loss in 0-10 cm soil layer are positively correlated. The traditional water and nitrogen treatment has large amounts of NO-3-N in 0-60 cm soil profiles, especially after the first two dressing. Based on the reduction of nitrogen, applying DCD helps reduce the NO-3-N accumulation, and nitrate leaching inhibitory effect is more obvious in 0-30 cm root zone. The N apparent loss in 0-30 cm soil layer and vegetables system of the traditional water nitrogen treatment is significantly higher than those of the other nitrogen treatments. Compared with the recommended water and nitrogen treatments ofⅠandⅡ, the applications of DCD with the recommended water and nitrogen treatments ofⅠandⅡcould reduce nitrogen surplus and loss rate of nitrogen. Compared with the traditional water and nitrogen management, cucumber yield and economic benefit are increased by 23.3% and 25560 yuan/ha respectively under the addition of DCD with the recommended water and nitrogen treatment Ⅱ(traditional water and nitrogen, N application rate was N 988.6 kg/ha and irrigation volume was 758.8 t/ha, the recommended water and nitrogen treatments of Ⅰ and Ⅱ, N application were N 709.4 and 746.9 kg/ha, and irrigation volume was 531.2 t/ha). 【Conclusions】Under this experimental condition, moderate reduction of nitrogen and water is feasible to satisfy the need of nitrogen for crop, reduce the surplus of nitrogen and increase the efficiency of nitrogen, and does not affect the output of crops. The DCD application(15% of the nitrogen rate)with recommended nitrogen Ⅱ under the controlled irrigation condition could not only reduce soil nitrogen surplus capacity, but also increase the economic benefit and environmental benefit effectively.