Combined appilcation of controlled-release nitrogen fertilizer and water-soluble fertilizer to reduce N₂O emission in greenhouse soil

Objectives Controlling N₂O emission is an important task in nitrogen management during crop production. Under drip irrigation condition, we studied the mechanism of controlled release fertilizer reducing N₂O emission, and the possibility of reducing total nitrogen input through replacement of basal applied urea by controlled-release fertilizer.

Methods A micro-plot field experiment was conducted inside greenhouse for consecutive three years, using tomato cultivar of 'Shengshihuihuang' as test material. 40% of nitrogen were basal applied before transplanting and 60% were top dressed with drip irrigation. Five treatments included no nitrogen input control (CK), routine N rate with urea basal applied (N 440 kg/hm², U), 20% less N input with urea basal applied (N 376 kg/hm², –20%U), routine N rate with controlled-release fertilizer basal applied (N 440 kg/hm², CRU) and 20% less N input with CRU basal applied (N 376 kg/hm², –20%CRU). Within the 15 days of basal application, soil gas samples were collected every day, within 8 days of each topdressing, the gas sample were collected every other days and collected three times, and the N₂O emission flux was measured by static box-chromatography method. Soil samples were collected at the 40, 80 and 120 days after transplanting, and soil physical and chemical properties were measured using conventional methods, and the number of related microbe and functional genes were measured by real-time fluorescence quantitative method. At harvest, the tomato yields were investigated and the nitrogen contents were determined.

Results Compared with U treatment, CRU treatments postponed the appearance of peak N₂O emission after basal fertilization from 8–13 days to 28–32 days, and significantly reduced peak emission flux. After topdressing, the peak emission occurred in 3–5 days in all treatments, while the two CRU treatments reduced the peak N₂O emission flux. Under the same amount of N input, the CRUs significantly reduced N₂O emission flux and NO₃^– accumulation in soil during basal and topdressing fertilizer stages. The total soil N₂O emission was significantly reduced by 24.8% in CRU treatment, and by 22.1% in –20%CRU treatment during the whole growing season; the content of NH₄⁺-N and NO₃⁻-N and the number of AOA amoA, AOB amoA and nirK were significantly reduced, the number of nirS was also reduced during growing season. Compared with U treatment, the yield and economic benefit of tomato were significantly increased in CRU treatment, and the yield in –20%U treatment was not changed significantly, while the economic benefit were increased.

Conclusions Replacing urea with controlled-release fertilizer as basal fertilizer could significantly delay the appearance of peak N₂O emission and emission intensity at the early stage of tomato growth, and reduce more than 20% of total N₂O emission during the whole growth period. The reason for it is the decreased NH₄⁺-N and NO₃⁻-N contents and the number of microbial related to nitrification and denitrification in soil. The total nitrogen fertilizer input could be properly reduced if use slow-release fertilizer as basal fertilizer in tomato under drip irrigation.