N fertilizer application rate, maize grain yield, N balance, and GHG emission intensity of N fertilizer use, N fertilizer production and other sources in different agro-ecological subregions.

a<p>n: number of observations.</p

Regional differences (±%) in N application rates, grain yield, and GHG emission intensity between the regional N management approach and farmers' practice in the 12 agroecological subregions.

<p>Regional difference (±%)  =  (regional approach minus farmers' practice)/farmers' practice ×100.</p

Establishing a Regional Nitrogen Management Approach to Mitigate Greenhouse Gas Emission Intensity from Intensive Smallholder Maize Production

<div><p>The overuse of Nitrogen (N) fertilizers on smallholder farms in rapidly developing countries has increased greenhouse gas (GHG) emissions and accelerated global N consumption over the past 20 years. In this study, a regional N management approach was developed based on the cost of the agricultural response to N application rates from 1,726 on-farm experiments to optimize N management across 12 agroecological subregions in the intensive Chinese smallholder maize belt. The grain yield and GHG emission intensity of this regional N management approach was investigated and compared to field-specific N management and farmers' practices. The regional N rate ranged from 150 to 219 kg N ha⁻¹ for the 12 agroecological subregions. Grain yields and GHG emission intensities were consistent with this regional N management approach compared to field-specific N management, which indicated that this regional N rate was close to the economically optimal N application. This regional N management approach, if widely adopted in China, could reduce N fertilizer use by more than 1.4 MT per year, increase maize production by 31.9 MT annually, and reduce annual GHG emissions by 18.6 MT. This regional N management approach can minimize net N losses and reduce GHG emission intensity from over- and underapplications, and therefore can also be used as a reference point for regional agricultural extension employees where soil and/or plant N monitoring is lacking.</p></div

Maize grain yield and fertilizer economic components of calculated net return across N rates using the regional N management approach indicated at the 2.05 price ratio (N price 4.87 yuan kg⁻¹ and maize price 2.37 yuan ha⁻¹) in the 12 agroecological subregions.

<p>In total, 1,726 N responses trials were used to estimate the regional N rate. The net return is the increase in yield times the grain price at a particular N rate, minus the cost of that amount of N fertilizer. The maximum return is the N rate at which the net return is greatest.</p

The number of on-farm experiments, maize yield without N, medium N rate, grain yield at the medium N rate and N rate, grain yield, GHG emission intensity of N fertilizer use, N fertilizer production and other sources for regional N management approach and field-specific N management.

a<p>n: number of observations.</p>b<p>Mean ± SD.</p>c<p>National values are computed from the regional values weighted by area. The regional weights are as follows:</p><p>NE1, 4.5%; NE2, 14.9%; NE3, 4.7%; NE4, 6.4%; NCP1, 25.6%; NCP2, 6.0%; NW1, 10.4%; NW2, 7.3%; NW3, 2.6%; SW1, 3.5%; SW2, 7.9%; SW3, 6.2%.</p

Maize production, N fertilizer consumption and total GHG emission between the regional N rate and farmers' practice in 12 agro-ecological subregions.

a<p>Different mean the different of maize production, N fertilizer consumption, and total GHG emission between regional N rate and farmer's practice.</p>b<p>National values are computed from the regional values weighted by area. The regional weights are as follows:</p><p>NE1, 4.5%; NE2, 14.9%; NE3, 4.7%; NE4, 6.4%; NCP1, 25.6%; NCP2, 6.0%; NW1, 10.4%; NW2, 7.3%; NW3, 2.6%; SW1, 3.5%; SW2, 7.9%; SW3, 6.2.</p

In-Season Root-Zone N Management for Mitigating Greenhouse Gas Emission and Reactive N Losses in Intensive Wheat Production

Although both the grain yields and environmental costs of nitrogen (N) fertilization are gaining more public and scientific debate, the complex linkages among crop productivity, N application rate, environmental footprints, and the consequences of improved N management are not well understood. We considered the concept of linking greenhouse gas (GHG) emission, reactive N losses, and N fertilizer application rates with crop productivity to determine the response of the GHG emission and reactive N losses to N surplus and further evaluated the potential to reduce these N environmental footprints by in-season root-zone N management. A meta-analysis suggested an exponential increase in the response of direct N₂O emissions and nitrate leaching to an increasing N surplus, while NH₃ volatilization increased linearly with an increasing N application rate for intensive wheat production in north China. The GHG emission and reactive N losses during N fertilizer application increased exponentially with an increasing N surplus. By pooling all 121 on-farm experimental sites, an in-season root-zone N management strategy was shown to reduce the N application rate by 61% from 325 kg N ha^–1 to 128 kg N ha^–1 compared to the farmers’ N practice, with no loss in wheat grain yield. As a result, the intensity of GHG emission and reactive N losses were reduced by 77% and 80%, respectively. The intensity of GHG emission and reactive N losses can be further reduced due to the improved N recovery and increased grain yield achieved by best crop management. In conclusion, N recovery efficiency and yield improvements should be used to reduce future agricultural N environmental footprints, rather than reducing the N application rate

Maize spike leaf N concentration as affected by three plant densities under the 70%ONR, ONR, and 130%ONR N-management schemes at the silking stage during the two-year study.

<p>Lower case letters indicate significant differences between treatments at the P< 0.05 level.</p

N fertilizer application rate (kg N ha⁻¹) of different N treatments applied at sowing, six-leaf (V6) and silking (VT) stages during the two-year study.

<p>The N treatments included a no N control (0 N), the optimal N rate based on in-season root zone N management (ONR), 70% ONR, 130% ONR, and farmers’ standard N practice (FNP).</p

Maize biomass, grain and straw N concentration, N uptake, and uptake efficiency at harvest in 2013 and 2014 for plant densities of 6.0, 7.5, and 9.0 plants m^–2, and all N treatments.

<p>N treatments included a no N control (0 N), optimal N rate based on in-season root zone N management (ONR), 70%ONR, 130%ONR, and farmers’ standard N practice (FNP).</p