A Spatiotemporal Assessment of County-Level Agronomic and Environmental Indicators for Maize Production in the US Midwest.

Achieving efficient and environmentally sustainable agricultural systems is a key issue for the US Midwest, the world’s largest maize producer. However, few studies have linked yield performance at the county-scale with resource use efficiency and environmental indicators using multi-criteria analysis to advance sustainable intensification efforts for this region. The objectives of this study were to i) benchmark US Midwest corn production performance using county-level agronomic and environmental indicators based on publicly available data, ii) evaluate the spatial and temporal variation of these indicators from 1995-2012, and iii) analyze the effects of climate and edaphic variables on selected indicators. We calculated the following indicators for Illinois, Indiana, and Iowa: yield gaps (Yg) (defined as average field-level yields subtracted from the 90^th percentile of yields using a previously published database), yield stability (defined by two variables, minimum yield potential (Myp) across an environmental index and coefficient of variation (Cv)), water productivity (Wp), nitrogen partial productivity (Npp), and nitrogen surplus (Ns) (defined as nitrogen inputs minus nitrogen harvested in grain). Preliminary results show that average values of Yg ranged from 13 to 35%, Myp from 1.8 to 8.5 Mg ha^-1, Wp from 9.7 to 17 kg mm^-1, Npp from 28.6 to 81 kg corn kg^-1 N, and Ns up to 42 kg ha^-1. Except for Npp, all the variables increased from the period 1995-1999 to 2008-2012 across the study region: Yg (7%), Wp (11%) and Ns (5%). We evaluated the effect of soil organic carbon, available water in the root zone, and precipitation during 80-120 days after planting on Yg and Myp with geographically weighted regressions (GWR). Fitted GWR models showed that predictor variables had a significant effect on the indicators depending on geographic regions (R2 of GWR models ranged from 0.43 to 0.88 for Yg and 0.67 to 0.88 for Myp). The results of this study are among the first to relate sustainability metrics such as the resiliency of crop yields in the US Midwest with other agronomic and environmental goals, while also assessing how environmental factors influence these indicators.