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Net Biome Productivity of Irrigated and Rainfed Maize–Soybean Rotations: Modeling vs. Measurements

^a Dep. of Renewable Resources, Univ. of Alberta, Edmonton, AB, Canada T6G 2E3
^b Dep. of Agronomy and Horticulture, Univ. of Nebraska, Lincoln, NE 68583-0915
^c School of Natural Resources, Univ. of Nebraska, Lincoln, NE 68583-0728

View larger version (22K): [in this window] [in a new window]   Fig. 1. (a) Recorded solar radiation and air temperature (Ta); (b) recorded precipitation, irrigation, and vapor pressure deficit (D); and (c) measured (symbols) vs. modeled (lines) water content of the Tomek soil at 0.10 m () (Table 1) during DOY 218–227 (6–15 August) 2002 at Mead, NE.

View larger version (26K): [in this window] [in a new window]   Fig. 2. (a) Canopy stomatal conductance (gc), (b) latent heat fluxes (LE), and (c) CO2 fluxes measured (squares) or gap-filled (diamonds) and modeled (lines) over irrigated and rainfed soybean during DOY 218–227 (6–15 August) 2002 at Mead, NE. Positive and negative values denote downward and upward fluxes, respectively.

View larger version (21K): [in this window] [in a new window]   Fig. 3. (a) Recorded solar radiation and air temperature (Ta); (b) recorded precipitation, irrigation, and vapor pressure deficit (D); and (c) measured (symbols) vs. modeled (lines) water content of the Tomek soil at 0.10 m () (Table 1) during DOY 221–230 (9–18 August) 2003 at Mead, NE.

View larger version (25K): [in this window] [in a new window]   Fig. 4. (a) Canopy stomatal conductance (gc), (b) latent heat fluxes (LE), and (c) CO2 fluxes measured (squares) or gap-filled (diamonds) and modeled (lines) over irrigated and rainfed maize during DOY 221–230 (9–18 August) 2003 at Mead, NE. Positive and negative values denote downward and upward fluxes, respectively.

View larger version (33K): [in this window] [in a new window]   Fig. 5. Response of CO2 fluxes to solar radiation (a, c) measured and (b, d) modeled over irrigated and rainfed (a, b) soybean during DOY 200–250, 2002 and (c, d) maize during DOY 195–255, 2003, when LAI > 2.5.

View larger version (21K): [in this window] [in a new window]   Fig. 6. Daily net ecosystem productivity (NEP) of irrigated and rainfed (a) soybean in 2002 and (b) maize in 2003 calculated from gap-filled eddy covariance fluxes (symbols) and modeled (lines) at Mead, NE. Vertical lines indicate periods shown in Fig. 1–4.

View larger version (23K): [in this window] [in a new window]   Fig. 7. Soil CO2 effluxes measured (symbols) and modeled (lines) in irrigated and rainfed (a) soybean in 2002 and (b) maize in 2003. Negative values denote upward fluxes.

View larger version (14K): [in this window] [in a new window]   Fig. 8. Aboveground total and reproductive phytomass measured (symbols) and modeled (lines) in irrigated and rainfed (a) soybean in 2002 and (b) maize in 2003 at Mead, NE.

View larger version (9K): [in this window] [in a new window]   Fig. 9. Soil + litter C of irrigated and rainfed maize–soybean rotations modeled to depths of 0.2 and 2 m under repeating 4-yr weather sequences (2001–2004) recorded at Mead, NE.