Net Primary Production of U.S. Midwest Croplands From Agricultural Harvest Yield Data

Abstract

We studied crop harvested yield, as recorded in national agricultural statistics, to estimate net primary production (NPP) in agricultural regions where most of the land area is sown with a few, well-studied crops. We estimated the magnitudes and interannual variations in NPP in croplands in the U.S. Midwest using crop area and yield data obtained from the U.S. National Agricultural Statistics Service (NASS). Total NPP, including estimates of the above-and belowground components, was calculated from harvested-yield data by (1) conversion from reporting units of yield of the crop product (usually in volume) to mass, (2) conversion from fresh mass to dry mass, (3) estimation of aboveground yield using crop harvest indices, defined as the ratio of economic product (e.g., grain) dry mass to plant aboveground dry mass, and (4) estimation of belowground yield as a function of aboveground biomass. This approach is applied to corn, soybean, sorghum, sunflower, oats, barley, wheat, and hay in Illinois, Indiana, Iowa, Wisconsin, Michigan, Minnesota, North Dakota, and Ohio for 1992, and in Iowa for 1982 through 1996. Many counties in the eight states had Ͼ70% coverage of these crops. In Iowa, corn and soybean accounted for Ͼ50% of the land area in most counties. County-level NPP in 1992 ranged from 4 Mg·ha Ϫ1 ·yr Ϫ1 biomass (ϫ0.5 in terms of carbon) in North Dakota, Wisconsin, and Minnesota to Ͼ17 Mg·ha Ϫ1 ·yr Ϫ1 in central Iowa, Illinois, and Ohio. Areas of highest NPP were dominated by corn and soybean cultivation. NPP for counties in Iowa varied among years by a factor of 2, with the lowest NPP in 1983 (which had an unusually wet spring), in 1988 (which was a drought year), and in 1993 (which experienced floods). A sensitivity analysis, conducted by varying harvest index and root:shoot ratio by 10-50%, indicated that the limit of accuracy of the method is ϳ1 Mg·ha Ϫ1 ·yr Ϫ1 .

The human carbon budget: an estimate of the spatial distribution of metabolic carbon consumption and release in the United States

“…Methods have been developed for estimating carbon uptake by agricultural crops Lobell et al 2002;Prince et al 2001). These methods can be used to estimate carbon uptake at the county level within the US.…”

Multi-scale evaluation of light use efficiency in MODIS gross primary productivity for croplands in the Midwestern United States

“…To exclude regions with sparse agriculture, our analysis was confined to counties with at least 10% of the total area planted in corn and soybean (661 counties were analyzed). Following methods outlined in previous agricultural studies (Prince et al, 2001;Reeves et al, 2005), we translated the reported grain productions to annual GPP. The translation takes equations that are analogous to the allometric equations for forest biomass estimation as follows:…”

The potassium paradox: Implications for soil fertility, crop production and human health

“…In the case of the unfertilized (NA-series) subplots, crop K removal was intensified by the harvest of corn or oats stover until 1967, estimated at 331 kg K ha − 1 for continuous corn, 310 kg K ha − 1 for the corn-oats rotation, and 256 kg K ha − 1 for the corn-oatshay rotation. To account for K removal in these residues, a harvest index of 0.5 was assumed for both crops [29][30][31][32] , and a K concentration of 13.5 (corn) or 15 (oats) kg Mg − 1 of dry matter 33 .…”

“…The importance of non-exchangeable and mineral K for plant uptake is by no means unique to micaceous clays, which are subject to biological weathering in the rhizosphere [91][92][93][94] (see also supplemental references [28] and [31] for the online version of the paper). Sand-and siltsized muscovite and biotite can also be a major source of plant-available K, as demonstrated conclusively by Mengel et al 83 in studies with 14 loess-derived Alfisols.…”