Objectives Replacing conventional urea with slow and controlled release urea (CRU) is an important way to harmonize high crop yields and N₂O emissions in farmland, however, the relevant research results are not always consistent. We summarized the comprehensive effects of slow and controlled release urea on wheat yield and N₂O emissions, as well as the key influencing factors through Meta analysis. The purpose is to provide a theoretical basis for optimizing nitrogen application strategies for wheat in different ecological regions.

Methods Literature, published across 2005 to July 2015, was searched in CNKI and Web of Science Data, using key words like controlled-release fertilizer, slow-release fertilizer, slow and controlled-release fertilizer, wheat, yield, N₂O, greenhouse gas. A total of 1458 papers were searched. Then the papers were refined using some criteria like ①containing CRU and common urea treatments at the same time; ②At least reported one wheat productivity index or N₂O emission; ③field experiment in mainland of China, were used to screen the qualified paper. At last, 91 papers were screened out, and 1311 pairs of data were extracted, including 535 for yield, 249 for nitrogen apparent use efficiency (NUE), 305 for nitrogen agronomic efficiency(NAE), 92 for biomass, 88 for production profit, and 42 for N₂O emission. Additionally, the application effects of CRU were analyzed under different climate, basic soil fertility, nitrogen application rate, and operation proportion.

Results In terms of the gross effect, replacing part of conventional urea with CRU significantly increased wheat yield (by 4.46%), NUE (by 12.20%), NAE (by 17.77%), and production profit (by 12.21%), and significantly reduced the total field N₂O emissions (-26.69%), however, there was no significant impact on the above ground biomass of wheat. Through relative significance analysis, it was found that the N application rate, the proportion of top dressing, and soil total N content were the key factors influencing the yield increasing effect of CRU. Overall, CRU exhibited better effect at decreased N fertilizer application rate, higher proportion of top dressing, and higher soil total N content. Moreover, CRU was recorded higher yield effect when the cumulative precipitation within wheat growing season is <450 mm, the planting density is ≤220 plants/m², and applied on wheat cultivars excluding weak gluten ones, In addition, the yield increasing effect of CRU is more pronounced when soils with low clay content and organic matter less than 20 g/kg. Under various conditions, CUR declined the total N₂O emissions from soil significantly, relative to conventional nitrogen fertilizer. The reduction of N₂O emission by CRU were particular pronounced when the substitution proportion of CRU>70%, soil organic matter content >20 g/kg, and soil clay content relatively high.

Conclusions Replacing partial conventional nitrogen fertilizer with CRU significantly increase nitrogen fertilizer utilization efficiency, wheat yield and production profit, and substantially reduce N₂O emissions in wheat fields. The application effect is closely related to climate conditions, cultivar types, application rate and methods, and soil properties. CRU are strongly recommended in areas with low precipitation during the wheat growing season, for medium, med-strong and strong gluten wheat cultivars, in sandy, loam, and clay loam soils, When replacing conventional nitrogen fertilizer with CRU, the total nitrogen application rate and planting density should be appropriately reduced. High proportion of CRU and top dressing is more conducive to coordinate high wheat yields and reduced N₂O emissions in wheat fields.