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

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

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

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

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

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

Cumulative biomass production.

<p>A, B: total plant biomass of wheat, and faba bean; C, D: shoot biomass of wheat, and faba bean; E, F: root biomass of wheat, and faba bean. iso: isolated plants; mono: monocropped plants; inter: intercropped plants. Open and solid circles, open triangles indicate the mean of actual data at each sampling. All values represent means±SE (n = 3). Curves are derived from the logistic equation using the mean of three replicates.</p

Instantaneous rate of biomass production (A, C, E), and instantaneous rate of nitrogen (N) uptake (B, D, F).

<p>A, B: total rate of biomass production and N uptake by wheat and faba bean of different planting systems. C, D: shoot growth rate and instantaneous per capita N uptake by shoot of wheat and faba bean. E, F: root growth rate and instantaneous per capita N uptake by root of wheat and faba bean. iso w: isolated wheat; mono w: monocropped wheat; iso f: isolated faba bean; inter w: intercropped wheat; inter f: intercropped faba bean.</p

Reducing carbon: phosphorus ratio can enhance microbial phytin mineralization and lessen competition with maize for phosphorus

<div><p>We tested the hypothesis that reducing the carbon (C):Phosphorus (P) ratio in rhizosphere soil would reduce bacterial competition with the plant for P from phytin, which would then increase phytin use efficiency for the plant. A three-factor pot experiment was carried out to study the effect of inoculation with a phytin-mineralizing bacterium, <i>Pseudomonas alcaligenes</i> (PA), on maize P uptake from phytin. Two levels of organic P, two levels of inorganic P, and three different PA inoculation treatments were used. When maize plants were grown in low available P soil with phytin, PA transformed soil P into microbial biomass P, which caused competition for available P with plant and inhibited plant uptake. When 5 mg P kg⁻¹ as KH₂PO₄ was added, inoculation with PA increased soil acid phosphatase activity which enhanced the mineralization rate of phytin. PA mobilized more P than it immobilized in microbial pool and enhanced plant P uptake. We conclude that the decreased C:P ratio by adding small amount of inorganic P in the rhizosphere could drive phytin mineralization by the bacteria and improve plant P nutrition.</p></div

Times and rates of maximum instantaneous biomass production and nitrogen uptake by wheat and faba bean estimated by a logistic model (Eqn 1).

<p>Note: A logistic model was fitted separately to the mean of three replicates of total plant, shoot and root. Iso indicates isolated plants; Mono indicates monocropped plants; Inter indicates intercropped plants.</p><p>Times and rates of maximum instantaneous biomass production and nitrogen uptake by wheat and faba bean estimated by a logistic model (Eqn 1).</p