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 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. In this study, we firstly compare the maize and soybean planted area from cropland data layer (CDL) with NASS area statistics over the CONUS during 2008-2018, and evaluate the interannual changes of planted and harvested area based on the two datasets. Secondly, we investigate the relationship between grain production and gross primary production (GPP) simulated by Vegetation Photosynthesis Model (VPM) at national and county scales. Finally, we evaluate the linear regression models between grain production and cumulated GPPVPM over time at 8-day resolution. We found strong spatial-temporal consistency between CDL and NASS datasets in maize and soybean planted areas. Maize and soybean planted areas increased by mid-2010s, largely driven by markets and international trade. Severe summer drought in 2012 had little impact on soybean planted and harvested area and maize planted area, but substantially reduced maize harvested area. and grain production. Annual county-level GPPVPM had strong linear relationship with NASS grain production for maize and soybean. The Harvest Index, defined as the ratio between grain production and GPPVPM (HIGPP_VPM), 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 cumulated GPPVPM (GPPVPM_CUM) over time at 8-day resolution showed that by the end of July, GPPVPM_CUM accounted for ~90% of variance in maize and soybean grain production, which was approximately two months before farmers started to harvest. This study clearly shows that VPM and GPPVPM data are useful for monitoring and in-season forecasting of maize and soybean grain production in the CONUS.