Can knowledge‐based N management produce more staple grain with lower greenhouse gas emission and reactive nitrogen pollution? A meta‐analysis

Abstract

Knowledge-based nitrogen (N) management, which is designed for a better synchronization of crop N demand with N supply, is critical for global food security and environmental sustainability. Yet, a comprehensive assessment on how these N management practices affect food production, greenhouse gas emission (GHG), and N pollution in China is lacking. We compiled the results of 376 studies (1166 observations) to evaluate the overall effects of seven knowledge-based N management practices on crop productivity, nitrous oxide (N O) emission, and major reactive N (Nr) losses (ammonia, NH ; N leaching and runoff), for staple grain (rice, wheat, and corn) production in China. These practices included the application of controlled-release N fertilizer, nitrification inhibitor (NI) and urease inhibitor (UI), higher splitting frequency of fertilizer N application, lower basal N fertilizer (BF) proportion, deep placement of N fertilizer, and optimal N rate based on soil N test. Our results showed that, compared to traditional N management, these knowledge-based N practices significantly increased grain yields by 1.3-10.0%, which is attributed to the higher aboveground N uptake (5.1-12.1%) and N use efficiency in grain (8.0-48.2%). Moreover, these N management practices overall reduced GHG emission and Nr losses, by 5.4-39.8% for N O emission, 30.7-61.5% for NH emission (except for the NI application), 13.6-37.3% for N leaching, and 15.5-45.0% for N runoff. The use of NI increased NH emission by 27.5% (9.0-56.0%), which deserves extra-attention. The cost and benefit analysis indicated that the yield profit of these N management practices exceeded the corresponding input cost, which resulted in a significant increase of the net economic benefit by 2.9-12.6%. These results suggest that knowledge-based N management practice can be considered an effective way to ensure food security and improve environmental sustainability, while increasing economic return.

Enhanced‐efficiency fertilizers are not a panacea for resolving the nitrogen problem

“…The tradeoff of NI in increasing NH 3 emission, as reported previously (Qiao et al., ; Xia et al., ), was present for all cropping systems and varied from a low of 13% in grassland to a high of 28% in dryland systems (Figure a). The net result, in terms of aggregated N‐loss reduction, was 52, 6, and 7 kg/ha for grassland, dryland, and paddy systems (Table S11).…”

Simultaneous quantification of N2, NH3 and N2O emissions from a flooded paddy field under different N fertilization regimes

“…Overall, the lower N 2 emissions during the TF and PIF periods gradually outweighed the higher emissions during the BF period (Figure S7), resulting in lower cumulative N 2 emissions for the IA treatment compared with the SA treatment over the entire rice‐growing season (Figure ). These results also indicate that reducing the basal N fertilizer proportion but increasing the proportion to the later (tillering and panicle initiation) growth stages of rice, has high potential to further reduce the N 2 and NH 3 emissions from flooded paddy fields as this crop N demand and N supply is better synchronized (Xia, Lam, et al, ).…”

“…Compared with the incorporation method, surface applied N requires a longer time to diffuse into soils and participate in nitrification–denitrification processes, thereby decreasing N 2 emissions during the BF period (Xia, Lam, et al, ). Nevertheless, the incorporation of basal N fertilizer into the soil can gradually enhance root activity during the early stages of rice growth (Zhang et al, ).…”

“…Quantifying N 2 emissions from flooded paddy fields is therefore an essential prerequisite for the development of improved N management to increase fertilizer N use efficiency (Wang et al, ; Zistl‐Schlingmann et al, ). In addition to N 2 emission, ammonia (NH 3 ) emission is another major gaseous N loss pathway in paddy fields, which, in contrast to N 2 emissions, has been well studied during the past two decades (Xia, Lam, et al, ; Zhao et al, ). Overall, in a 3‐year paddy rice field experiment in southern China, Zhao et al () estimated, using a 15 N tracer method, that the emission of N 2 and NH 3 represented 51.9% of the fertilizer N broadcast on the soil surface, whereas the loss of N via hydrological pathways (e.g., N leaching and runoff) only accounted for 7.4%.…”

Evaluation of the Agronomic Impacts on Yield-Scaled N2O Emission from Wheat and Maize Fields in China

“…Therefore, integrating assessment on both N 2 O emissions and crop yield is essential in optimizing cropping practices. Although many studies have evaluated the impact and mitigation potential of cropping practices on N 2 O emission [15][16][17][18][19][20][21][22], few studies have been linked to crop yield [23][24][25]. Recent studies suggest that comprehensive assessments of cropping practices per unit yield (yield-scaled) rather than land area (area-scaled) could benefit sustainable intensification of cropping practices and policy selection with a trade-off of N 2 O emission mitigation and food security [23,24,26].…”