Spatial-temporal dynamics of maize and soybean planted area, harvested area, gross primary production, and grain production in the Contiguous United States during 2008-2018

Abstract:

The United States of America ranked first in maize export and second in soybean export among the countries in the world. Accurate and timely data and information on maize and soybean production in the Contiguous United States (CONUS) are important for food security at the regional and global scales. There is a need to better understand the spatial-temporal dynamics of maize and soybean production in the CONUS under changing climate, land use, and market. In this study, we evaluate the interannual dynamics of maize and soybean planted area and harvested area in the CONUS during 2008-2018. We find the increases of maize and soybean planted areas in mid-2010s, driven by markets and international trade. The results also show that severe summer drought in 2012 had little impacts on soybean planted and harvested areas and maize planted area, but it substantially reduced maize harvested area and grain production. We use the Vegetation Photosynthesis Model (VPM), the Crop Data Layer (CDL), climate, and image data to estimate 8-day gross primary production (GPP) of maize and soybean in the CONUS during 2008-2018 (GPP_VPM). Annual GPP_VPM (GPP_{VPM_Year}) had strong linear relationships with maize and soybean grain production from the agricultural statistic data at the county scale. The Harvest Index, defined as the ratio between grain production and GPP_VPM (HI_{VPM_GPP}), ranged from 0.25 (2012) to 0.36 for maize and from 0.13 to 0.15 for soybean. The linear regression models between grain production and cumulative GPP_VPM (GPP_{VPM_acc}) over time at 8-day resolution show that by the end of July, GPP_{VPM_acc} accounted for ~90% of variance in maize and soybean grain production during 2008-2018 at the county scale, which was approximately two months before farmers started to harvest maize and soybean. Our findings suggest that the VPM and GPP_VPM data product are useful tools and data for farmers, decision makers, stakeholders and the public.