Baseline measurements of field sites are necessary before imposing contrasting treatments in long-term studies. In preparation for the Long-Term Agroecosystem Research Network – Croplands Common Experiment, we imposed business-as-usual (BAU) cropping practices on two 20 ha fields near Mandan, North Dakota, USA. We sought to quantify potential differences between fields for a suite of agronomic and environmental attributes. For three years (2016–2018), both fields were planted to a spring wheat (Triticum aestivum L.) – corn (Zea mays L.) – soybean (Glycine max L.) rotation under no-till management. We used eddy covariance techniques for continuous monitoring of field-level carbon, water, and heat fluxes in conjunction with periodic in-field measurements (n=10 per field) of aboveground biomass (AGB), leaf area index (LAI), and canopy height (CHt).
Results/Conclusions
Daily net ecosystem exchange (NEE) for carbon, evapotranspiration (ET) and sensible heat flux (H) were similar between fields. Likewise, patterns of in-field attributes during the growing season for each crop were similar for both fields. Annual sums of NEE (mean ± se, g C m-2 yr-1) across crops were near equilibrium with the atmosphere and comparable between fields (11 ± 42 versus −28 ± 68) despite differences between fields in annual NEE for corn (2017). Additionally, both annual ET (mean ± se, mm yr-1) and daily H (mean ± se, W m-2) across crops did not differ between fields, with values of 400 ± 16 versus 435 ± 29 mm yr-1 and 19.8 ± 1.9 versus 19.9 ± 2.4 W m-2, respectively. However, AGB, maximum LAI, and CHt were different between fields at the end of growing season in soybean (2018). Stratification of the flux footprint into 12 wind sectors and 6 radii indicated that variations of Landsat-NDVI between fields were correlated through an upwind distance of 120 to 150 m from the eddy covariance sensors (R2: 0.50, 0.83, 0.61 for wheat, corn, soybean, respectively). We will map the variations of in-field attributes using Landsat-NDVI.