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Remote Sensing-Informed Variable-Rate Nitrogen Management of Wheat and Corn

Agronomic and Groundwater Outcomes

^a Dep. of Agron., 209A Waters Hall, Univ. of Missouri, Columbia, MO 65211
^b Dep. of Soil Science, North Carolina State Univ., Raleigh, NC 27695-7619
^c Dep. of Crop Science, North Carolina State Univ., Raleigh, NC 27695-7620
^d Dep. of Statistics, North Carolina State Univ., Raleigh, NC 27695-8203

View larger version (37K): [in a new window]   Fig. 1. (a) Daily precipitation from June 2001 to August 2003 and (b) actual (January 2001–July 2003; bars) and 30-yr-average (1974–2003; line) monthly precipitation at the study site.

View larger version (47K): [in a new window]   Fig. 2. Comparisons of N applied, grain yield or aboveground biomass (forage), harvest N ratio, and surplus N for three N management treatments in a wheat–soybean–corn rotation from 2001 to 2003. Mean values are shown above the columns. Bars indicate +1 SE. Different letters above the bars indicate significant differences among estimated treatment means at the 0.05 probability level. RYE = uniform Realistic Yield Expectation N management; FA = remote sensing-informed, uniform, field-average N management; SS = remote sensing-informed, site-specific, variable-rate N management.

View larger version (63K): [in a new window]   Fig. 3. Nitrogen management treatment effects on groundwater NO3–N concentrations sampled biweekly from March 2001 to July 2003 at (a) 0.9- to 1.8-m, (b) 1.8- to 2.7-m and (c) 2.7- to 3.7-m depths. RYE = uniform Realistic Yield Expectation N management; FA = remote sensing-informed, uniform, field-average N management; SS = remote sensing-informed, site-specific, variable-rate N management. Different letters above bars indicates significant differences among the estimated treatment means at the 0.05 probability level. For cases where 0.05 < p < 0.10, the actual p value of the comparison is shown. The reference line is at 10 mg NO3–N L–1.

View larger version (37K): [in a new window]   Fig. 4. (a) Mean shallow groundwater NO3–N concentration averaged over the 0.9- to 1.8-, 1.8- to 2.7-, and 2.7- to 3.7-m depths and (b) field-average shallow water table depth measured from July 2001 to July 2003. Bars indicate (a) ±1 or (b) +1 SE. Tile drainage lines are at 1-m depth.