Closing the N-Use Efficiency Gap to Achieve Food and Environmental Security

Abstract

To achieve food and environmental security, closing the gap between actual and attainable N-use efficiency should be as important as closing yield gaps. Using a meta-analysis of 205 published studies from 317 study sites, including 1332 observations from rice, wheat, and maize system in China, reactive N (Nr) losses, and total N2O emissions from N fertilization both increased exponentially with increasing N application rate. On the basis of the N loss response curves from the literature meta-analysis, the direct N2O emission, NH3 volatilization, N leaching, and N runoff, and total N2O emission (direct + indirect) were calculated using information from the survey of farmers. The PFP-N (kilogram of harvested product per kilogram of N applied (kg (kg of N)(-1))) for 6259 farmers were relative low with only 37, 23, and 32 kg (kg of N)(-1) for rice, wheat, and maize systems, respectively. In comparison, the PFP-N for highest yield and PFP-N group (refers to fields where the PFP-N was within the 80-100th percentile among those fields that achieved yields within the 80-100th percentile) averaged 62, 42, and 53 kg (kg of N)(-1) for rice, wheat, and maize systems, respectively. The corresponding grain yield would increase by 1.6-2.3 Mg ha(-1), while the N application rate would be reduced by 56-100 kg of N ha(-1) from average farmer field to highest yield and PFP-N group. In return, the Nr loss intensity (4-11 kg of N (Mg of grain)(-1)) and total N2O emission intensity (0.15-0.29 kg of N (Mg of grain)(-1)) would both be reduced significantly as compared to current agricultural practices. In many circumstances, closing the PFP-N gap in intensive cropping systems is compatible with increased crop productivity and reductions in both Nr losses and total N2O emissions.

Factors Affecting Nitrogen Use Efficiency and Grain Yield of Summer Maize on Smallholder Farms in the North China Plain

“…Previous surveys of the PFP N of maize found values of 32 kg kg −1 [65] and 43 kg kg −1 [31]. We obtained a slightly higher PFP N of maize in smallholder farmers' fields of 49.1 kg kg −1 .…”

Evaluating four nitrous oxide emission algorithms in response to N rate on an irrigated corn field

“…7B). The relationships between N 2 O emissions and N rate were shown experimentally in the literature as nonlinear, such as in US Corn Belt (McSwiney and Robertson, 2005;Hoben et al, 2011) and in the North China Plain (Cui et al, 2013(Cui et al, , 2014b, or as linear, such as in Northern Colorado corn field Halvorson et al, 2008Halvorson et al, , 2014. The different relationships between N 2 O emissions and N rates may be related to the weather variations across seasons (such as 2003 versus 2004e2006 in the current study) and the excessive N application rates to crop N requirement, such as in North China Plain where exponential increase of N 2 O emissions was mainly related to the high soil N surplus caused by over-applied high N rate up to about 400e500 kg N ha À1 per crop (Cui et al, 2013(Cui et al, , 2014a.…”

Nitrogen use efficiency in modern wheat cultivars

“…The mineral N fertilizer represents a significant cost in wheat production and may cause negative impacts on the environment through leaching and N 2 O emissions (Cui et al 2014). Management practices to help farmers increase productivity and reduce production costs should be studied to ensure agricultural sustainability (Kaneko et al 2010).…”