Soil organic carbon (SOC) in agroecosystems is regulated by crop rotation and soil disturbance. We assessed crop sequence and tillage effects on SOC dynamics and storage using natural 13C abundance of corn (Zea mays L.) and soybean [Glycine max (L.), Merr.]. Treatments consisted of tillage: moldboard plow (MP), chisel plow (CP), and no‐tillage (NT); and crop sequence: continuous corn (CC), continuous soybean (SS), and alternating corn–soybean (CS). Soil samples were collected after 14 yr in each treatment and in fallow alley‐ways and were analyzed for SOC, δ13C, bulk density, and pH. Tillage by crop sequence interactions occurred as treatments with MP and SS as well as fallow averaged 135 Mg SOC ha−1 (0‐ to 45‐cm depth), while CP treatments with corn (CC and CS) and NT with CC averaged 164 Mg SOC ha−1 Crop sequence effects on SOC (0‐ to 45‐cm depth) occurred when tillage was reduced with CP and NT averaging 15% greater SOC in CC than SS. In addition to less C inputs than CC, SS accelerated rates of SOC decomposition. Tillage effects on SOC were greatest in CC where CP had 26% and NT 20% more SOC than MP, whereas SOC in SS was similar across tillage treatments. Up to 33% of the greater SOC under CC for CP and NT, compared with MP, occurred below tillage operating depths. Substantial losses of SOC were estimated (1.6 Mg SOC ha−1 yr−1) despite lowering SOC decay rates with reduced tillage and high levels of C inputs with CC.

Corn's (Zea mays L.) stover is a potential nonfood, herbaceous bioenergy feedstock. A vital aspect of utilizing stover for bioenergy production is to establish sustainable harvest criteria that avoid exacerbating soil erosion or degrading soil organic carbon (SOC) levels. Our goal is to empirically estimate the minimum residue return rate required to sustain SOC levels at numerous locations and to identify which macroscale factors affect empirical estimates. Minimum residue return rate is conceptually useful, but only if the study is of long enough duration and a relationship between the rate of residue returned and the change in SOC can be measured. About one third of the Corn Stover Regional Partnership team (Team) sites met these criteria with a minimum residue return rate of 3.9±2.18 Mg stover ha −1 yr −1 , The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the US Department of Agriculture or the Agricultural Research Service of any product or service to the exclusion of others that may be suitable. The USDA is an equal opportunity provider and employer.

Corn (Zea mays L.) stover was identified as an important feedstock for cellulosic bioenergy production because of the extensive area upon which the crop is already grown. This report summarizes 239 site-years of field research examining effects of zero, moderate, and high stover removal rates at 36 sites in seven different states. Grain and stover yields from all sites as well as N, P, and K removal from 28 sites are summarized for nine longitude and six latitude bands, two tillage practices (conventional vs no tillage), two stover-harvest methods (machine vs calculated), and two crop rotations {continuous corn (maize) vs corn/soybean [Glycine max (L.) Merr.]}. Mean grain yields ranged from 5.0 to 12.0 Mg ha−1 (80 to 192 bu ac−1). Harvesting an average of 3.9 or 7.2 Mg ha−1(1.7 or 3.2 tons ac−1) of the corn stover resulted in a slight increase in grain yield at 57 and 51 % of the sites, respectively. Average no-till grain yields were significantly lower than with conventional tillage when stover was not harvested, but not when it was collected. Plant samples collected between physiological maturity and combine harvest showed that compared to not harvesting stover, N, P, and K removal was increased by 24, 2.7, and 31 kg ha−1, respectively, with moderate (3.9 Mg ha−1) harvest and by 47, 5.5, and 62 kg ha−1, respectively, with high (7.2 Mg ha−1) removal. This data will be useful for verifying simulation models and available corn stover feedstock projections, but is too variable for planning site-specific stover harvest. Abstract Corn (Zea mays L.) stover was identified as an important feedstock for cellulosic bioenergy production because of the extensive area upon which the crop is already grown. This report summarizes 239 site-years of field research examining effects of zero, moderate, and high stover removal rates at 36 sites in seven different states. Grain and stover yields from all sites as well as N, P, and K removal from 28 sites are summarized for nine longitude and six latitude bands, two tillage practices (conventional vs no tillage), two stoverharvest methods (machine vs calculated), and two crop rotations {continuous corn (maize) vs corn/soybean [Glycine max (L.) Merr.]}. Mean grain yields ranged from 5.0 to 12.0 Mg ha −1 (80 to 192 bu ac −1 ). Harvesting an average of 3.9 or 7.2 Mg ha −1 (1.7 or 3.2 tons ac −1 ) of the corn stover resulted in a slight increase in grain yield at 57 and 51 % of the sites, respectively. Average no-till grain yields were significantly lower than with conventional tillage when stover was not harvested, but not when it was collected. Plant samples ( ) 7:528-539 DOI 10.1007 collected between physiological maturity and combine harvest showed that compared to not harvesting stover, N, P, and K removal was increased by 24, 2.7, and 31 kg ha −1 , respectively, with moderate (3.9 Mg ha −1 ) harvest and by 47, 5.5, and 62 kg ha −1 , respectively, with high (7.2 Mg ha −1 ) removal. This data will be useful for verifying simulation models and available corn stover feedstoc...

Corn (Zea mays L.) stover removal for biofuel production is expected to increase in the near future. Previous research suggests stover removal is best suited to continuous corn (CC) cropping systems with reduced tillage. However, grain yields in reduced tillage CC systems in the Upper Midwest can be reduced because of cool soil temperatures restricting early-season growth. Field experiments were conducted over 3 yr at two locations in southern Minnesota with medium-and fine-textured soils to assess the agronomic responses of CC to stover removal, tillage system, and fertilizer N rate. Stover removal and/or tillage increased soil temperature by as much as 4°C, and differences among treatments generally existed until canopy closure. Corn emergence was 6% greater with stover removal in no-tillage (NT), but was not affected by stover removal in chisel-tillage (CT) and strip-tillage (ST). Stover removal increased normalized difference vegetative index (NDVI) at the eight leaf collar stage (V8) by 20 and 13% in NT and ST, respectively, but had no effect on NDVI in CT. Stover removal decreased the economically optimum N rate (EONR) by >12 and >19 kg N ha -1 in NT and ST, respectively, and increased grain yield at the EONR by 7, 9, and 6% in CT, NT, and ST, respectively. These results indicate stover removal can improve short-term agronomic productivity of moderate-to high-yielding CC on productive soils in the Upper Midwest.

Year‐to‐year consistency of crop yields within a farm field is needed to use grain yield monitor data for site‐specific management decisions such as yield goals for fertilizer recommendations. A 5‐yr study was conducted from 1991 to 1995 to determine whether patterns of corn (Zea mays L.) grain yields are similar over a number of years and whether grain yields from one or more years can be used to predict grain yields for subsequent years. The experimental site was located at the Northern Cornbelt Sand Plain Management Systems Evaluation Area near Princeton, MN. The research area was 4.4 acres with soils mapped as three variants of the Zimmerman fine sand (mixed, frigid, argic, Udipsamment) and a Cantlin loamy fine sand (sandy, mixed, frigid, typic, Udipsamment). Continuous corn was grown from 1990 through 1995 after alfalfa (Medicago saliva L.) from 1981 through 1989. Cultural practices were applied uniformly to the 4.4 acre site each year. The 4.4 acres were divided into 60 grid cells (50 ft. by 60 ft.) and grain yields, corrected to 15.5% moisture, were determined by hand harvesting an area (two rows 20 ft. long) within each of the 60 grid cells. Differences between highest and lowest continuous corn grain yields in the research area were 72 bu/acre in 1991, 44 bu/acre in 1992, 45 bu/acre in 1993, 51 bu/acre in 1994, and 57 bu/acre in 1995. Grain yields were not spatially consistent from year to year. Areas with better grain yields were not consistent from year to year, and conversely, poor production areas were not found in similar locations each year. Only 4 to 42% of the grain yield variability for a given year is accounted for by a knowledge of the grain yields from a previous year. The lack of grain yield stability as measured by ranked correlations on a sandy soil raises serious questions for the potential for use of this information. The data indicate that the use of grain yield maps for fertilizer recommendations on a site specific basis may not be possible or may require a much longer term database than the normally recommended 5 yr, unless there is a construct of inputs that explains the grain yield patterns each year. Research Question With variable rate technology it is possible to make changes in the application of crop production inputs on the go. Fertilizer recommendations are often adjusted for yield goal. Therefore, it is important to have some measure of consistent yield patterns across a landscape. Are differences in yields across a field consistent over time? Can measured differences in yield be used to established more realistic yield goals? Literature Summary Growers usually know that certain areas of their production fields produce more yield than others. Until recently, the technology to measure and locate the variability of yields has not been available. Yield goals have been used to develop fertilizer recommendations in the Upper Midwest. Before the development of yield monitoring technology, yield goals were usually based on production information from entire fields. Now yield goals ...