A component of the USDA ARS Long-Term Agroecosystem Research (LTAR) network is a Common Experiment standardized across all sites. This collection contains all standardized protocols for the biophysical metrics collected in the Common Experiment.

Long-term research is essential for guiding the development of agroecosystems to meet escalating production demands in a manner that is environmentally sound and socially acceptable. Research must integrate biophysical and socioeconomic factors to provide geographically scalable knowledge that involves stakeholders across the research-education-extension-policy spectrum. In response to this need, the Long-Term Agroecosystem Research (LTAR) network developed a "Common Experiment," which seeks to develop and disseminate multi-region, science-based information to enable implementation of visionary agricultural innovations while simultaneously promoting food security, well-being, environmental quality, and climate adaptation and mitigation. The core design of the Common Experiment contrasts prevailing and alternative/aspirational production systems, with the latter including novel innovations hypothesized to advance sustainable intensification in locally appropriate ways. Treatments in the Common Experiment represent a diversity of production systems under cropland, grazing land, and integrated crop/grazing land management. Where possible, treatments are evaluated at multiple spatial scales (e.g., from plot to enterprise) and are designed to evolve over the course of the experiment with stakeholder input. A common assessment framework guides data collection for the experiment and is complemented by metric-specific protocols and an emerging data management infrastructure. Currently, there are large differences among sites in the application of the experimental framework and degree of stakeholder engagement; differences largely grounded in pragmatic issues related to land access, site expertise, and resource availability. The full potential of the LTAR Common Experiment may be realized with strategic investments in network capacity.

Climate smart agricultural practices have received considerable attention recently for their potential for climate change mitigation through sequestering atmospheric carbon. Despite the enthusiasm for climate smart practices, there is limited evidence they are more effective at removing carbon from the atmosphere and storing it in the soil than current practices. We hypothesized that a field with aspirational (ASP) practices (i.e., no-till corn-soybean-wheat-hay rotation with cover crops) would accumulate more soil organic carbon (SOC) versus a business-as-usual (BAU) field (i.e., conventional-tillage, corn-soybean-soybean rotation). We used deep soil cores (1 m) to assess changes in soil organic carbon (Delta SOC) between 2016 and 2022 for the two fields and compare with estimates based on eddy covariance calculation of Delta SOC. We found that the ASP field had Delta SOC that was positive, and larger than the BAU field. Both the soil sample method (Delta SOCSS) and the eddy covariance method (Delta SOCEC) agreed on this point, but the magnitude of Delta SOC was much larger when estimated with soil samples (Delta SOCSS was 1.9 +/- 1.7 % yr(-1) and-0.7 +/- 1.3 % yr(-1) at ASP and BAU, respectively) than with eddy covariance (Delta SOCEC was 0.80 +/- 0.09 % yr(-1) and 0.12 +/- 0.06 % yr(-1) at ASP and BAU, respectively). Finally, we used the continuous measurements of carbon fluxes from the eddy covariance towers to examine how conservation practices (cover crops, no-till, or expanded crop rotation) led to increased carbon storage. We found that unharvested cover crops add carbon to the soil that offsets net carbon losses that otherwise reduce soil carbon storage when the field is fallow. No-till and expanded crop rotations also affect the carbon budget of the agroecosystems. Results from this study illustrate the value of conservation practices in a changing climate and the value of eddy covariance measurements for assessing climate smart practices.

Winter cover crop performance metrics (i.e., vegetative biomass quantity and quality) affect ecosystem services provisions, but they vary widely due to differences in agronomic practices, soil properties, and climate. Cereal rye (Secale cereale) is the most common winter cover crop in the United States due to its winter hardiness, low seed cost, and high biomass production. We compiled data on cereal rye winter cover crop performance metrics, agronomic practices, and soil properties across the eastern half of the United States. The dataset includes a total of 5,695 cereal rye biomass observations across 208 site-years between 2001–2022 and encompasses a wide range of agronomic, soils, and climate conditions. Cereal rye biomass values had a mean of 3,428 kg ha−1, a median of 2,458 kg ha−1, and a standard deviation of 3,163 kg ha−1. The data can be used for empirical analyses, to calibrate, validate, and evaluate process-based models, and to develop decision support tools for management and policy decisions.

Understanding the relationship between water and production within and across agroecosystems is essential for addressing several agricultural challenges of the 21st century: providing food, fuel, and fiber to a growing human population, reducing the environmental impacts of agricultural production, and adapting food systems to climate change. Of all human activities, agriculture has the highest demand for water globally. Therefore, increasing water use efficiency (WUE), or producing 'more crop per drop', has been a long-term goal of agricultural management, engineering, and crop breeding. WUE is a widely used term applied across a diverse array of spatial scales, spanning from the leaf to the globe, and over temporal scales ranging from seconds to months to years. The measurement, interpretation, and complexity of WUE varies enormously across these spatial and temporal scales, challenging comparisons within and across diverse agroecosystems. The goals of this review are to evaluate common indicators of WUE in agricultural production and assess tradeoffs when applying these indicators within and across agroecosystems amidst a changing climate. We examine three questions: (1) what are the uses and limitations of common WUE indicators, (2) how can WUE indicators be applied within and across agroecosystems, and (3) how can WUE indicators help adapt agriculture to climate change? Addressing these agricultural challenges will require land managers, producers, policy makers, researchers, and consumers to evaluate costs and benefits of practices and innovations of water use in agricultural production. Clearly defining and interpreting WUE in the most scale-appropriate way is crucial for advancing agroecosystem sustainability.

Controlled drainage (CD) is a valuable management practice for reducing drainage volume and nutrient loss, but its impact on corn (Zea mays L.) production is not completely understood. The objectives of this study were to investigate the regional effect of CD on corn grain yield compared to free drainage (FD), investigate the factors influencing corn yield response to CD, provide management recommendations for optimizing corn yield under CD, and identify future research needs for corn production on poorly drained soils with subsurface drainage systems. This synthesis included data collected from 13 field sites where corn was planted under both FD and CD in six U.S. Midwestern states and North Carolina totaling 55 site-years of data from 2006 to 2017. On average, there was no statistically significant difference in corn grain yield between CD (10.62 Mg/ha) and FD (10.53 Mg ha−1). However, 42% of the dataset indicated that CD either increased or decreased corn yield by 4% or more compared to FD. Further analysis was conducted on this subset of data in order to evaluate underlying factors (i.e., weather conditions during the season, soil type, and drainage system design and management) influencing corn yield response to CD. Results of this analysis showed that CD was effective in alleviating plant stress caused by mild to moderate drought conditions and subsequently increased corn grain yield by 4–14% in 12 site-years. In contrast, CD reduced corn grain yield by 4–10% during wet growing seasons (6 site-years). Variability in growing season precipitation has been identified as a key factor influencing corn grain yield under CD, and more active management or CD system automation is recommended. General recommendations are provided for managing manually operated CD systems in the U.S. Midwest to improve growing season water management and corn yield. Additional research to develop technologically advanced water management systems for crop production on poorly drained soils is needed in order to adapt to changing weather patterns.

Abnormal ear development in corn (Zea mays L.) has been reported for more than 100 years. More recently, in 2016, widespread abnormal multiple ears per stalk node (herein termed as multi-ears), barbell ears, and short husks were reported in cornfields located in the western and central Corn Belt (Illinois, Iowa, Nebraska, and Kansas), Eastern Colorado, and the Texas Panhandle region in the United States. Little was known about the underlying causes of these abnormalities. A literature review examining conditions potentially affecting corn ear formation, yield, and abnormal ears was conducted. Several abnormal ear symptoms appear to be formed by stress conditions such as extreme weather, limited solar radiation, and responses to plant growth regulators. The accumulation of these effects can result in the abortion of primary ears and the development of secondary abnormal ears, which has been a hypothesis for the last 15 years. Whether or not primary ear abortion is one of the factors for abnormal ears remains a valid question. Abnormal ears can be understood as the result of an "expression triangle": susceptible genetics, conducive environmental conditions, and unfavorable management practices. Together, these factors can interact and cause abnormal ears and lower yields. Active knowledge gaps include the environmental and physiological pathways to abnormal ears, their impact on grain quality and yield, their effect on other processes such as dry-down and harvest ease, and an in-depth understanding of differing genetics, environment, and management.

The relationship between collared leaf number and growing degree days (GDD) is crucial for predicting maize phenology. Biophysical crop models convert GDD accumulation to leaf numbers by using a constant parameter termed phyllochron (°C-day leaf−1) or leaf appearance rate (LAR; leaf oC-day−1). However, such important parameter values are rarely estimated for modern maize hybrids. To fill this gap, we sourced and analyzed experimental datasets from the United States Corn Belt with the objective to (i) determine phyllochron values for two types of models: linear (1-parameter) and bilinear (3-parameters; phase I and II phyllochron, and transition point) and (ii) explore whether environmental factors such as photoperiod and radiation, and physiological variables such as plant growth rate can explain variability in phyllochron and improve predictability of maize phenology. The datasets included different locations (latitudes between 48° N and 41° N), years (2009–2019), hybrids, and management settings. Results indicated that the bilinear model represented the leaf number vs. GDD relationship more accurately than the linear model (R2 = 0.99 vs. 0.95, n = 4,694). Across datasets, first phase phyllochron, transition leaf number, and second phase phyllochron averaged 57.9 ± 7.5°C-day, 9.8 ± 1.2 leaves, and 30.9 ± 5.7°C-day, respectively. Correlation analysis revealed that radiation from the V3 to the V9 developmental stages had a positive relationship with phyllochron (r = 0.69), while photoperiod was positively related to days to flowering or total leaf number (r = 0.89). Additionally, a positive nonlinear relationship between maize LAR and plant growth rate was found. Present findings provide important parameter values for calibration and optimization of maize crop models in the United States Corn Belt, as well as new insights to enhance mechanisms in crop models.

This paper describes a multi-site and multi-decadal dataset of artificially drained agricultural fields in seven Midwest states and North Carolina, USA. Thirty-nine research sites provided data on three conservation practices for cropland with subsurface tile drainage: saturated buffers, controlled drainage, and drainage water recycling. These practices utilize vegetation and/or infrastructure to minimize off-site nutrient losses and retain water in the landscape. A total of 219 variables are reported, including 90 field measurement variables and 129 management operations and metadata. Key measurements include subsurface drain flow (206 site-years), nitrate-N load (154 site-years) and other water quality metrics, as well as agronomic, soil, climate, farm management and metadata records. Data are published at the USDA National Agricultural Library Ag Data Commons repository and are also available through an interactive website at Iowa State University. These multi-disciplinary data have large reuse potential by the scientific community as well as for design of drainage systems and implementation in the US and globally.

Drainage water recycling (DWR) involves capture, storage, and reuse of surface and subsurface drainage water as irrigation to enhance crop production during critical times of the growing season. Our objectives were to synthesize 53 site-years of data from 1996 to 2017 in the midwestern United States to determine the effect of DWR using primarily subirrigation on corn (Zea mays L.) grain yield and yield variability and to identify precipitation factors at key stages of corn development (V1-V8, V9-VT, R1-R2, R3-R4, and R5-R6) that correlated to an increase in yield with DWR. A generalized additive model was used to quantify and characterize the relationship between precipitation and corn grain yield during corn development stages and to determine if that relationship differed between DWR and free drainage (FD). Corn yield response to precipitation was generally similar between DWR and FD, except during the critical period of V9-R2, in which DWR was more resilient to precipitation extremes than FD. Drainage water recycling was generally more responsive than FD in years with low and normal precipitation (<181 mm). When precipitation was low (27-85 mm) from V9 to R2, DWR had higher yields (77% of the site-years evaluated), with an average yield increase of 3.6 Mg ha(-1) (1.2-7.5 Mg ha(-1)). Overall, FD had 28% greater yield variability than DWR. Additional research is needed on DWR impacts on different soils and locations throughout this region to improve the stability of corn yields and to develop automated DWR systems for enhancing efficiency of water management with increasing climate variability.

Increasing temperatures in the US Midwest are projected to reduce maize yields because warmer temperatures hasten reproductive development and, as a result, shorten the grain fill period. However, there is widespread expectation that farmers will mitigate projected yield losses by planting longer season hybrids that lengthen the grain fill period. Here, we ask: (a) how current hybrid maturity length relates to thermal availability of the local climate, and (b) if farmers are shifting to longer season hybrids in response to a warming climate. To address these questions, we used county‐level Pioneer brand hybrid sales (Corteva Agriscience) across 17 years and 650 counties in 10 Midwest states (IA, IL, IN, MI, MN, MO, ND, OH, SD, and WI). Northern counties were shown to select hybrid maturities with growing degree day (GDD°C) requirements more closely related to the environmentally available GDD compared to central and southern counties. This measure, termed “thermal overlap,” ranged from complete 106% in northern counties to a mere 63% in southern counties. The relationship between thermal overlap and latitude was fit using split‐line regression and a breakpoint of 42.8°N was identified. Over the 17‐years, hybrid maturities shortened across the majority of the Midwest with only a minority of counties lengthening in select northern and southern areas. The annual change in maturity ranged from −5.4 to 4.1 GDD year−1 with a median of −0.9 GDD year−1. The shortening of hybrid maturity contrasts with widespread expectations of hybrid maturity aligning with magnitude of warming. Factors other than thermal availability appear to more strongly impact farmer decision‐making such as the benefit of shorter maturity hybrids on grain drying costs, direct delivery to ethanol biorefineries, field operability, labor constraints, and crop genetics availability. Prediction of hybrid choice under future climate scenarios must include climatic factors, physiological‐genetic attributes, socio‐economic, and operational constraints.

Studies are limited that focus on change in concentration and accumulation of secondary and micronutrients in corn (Zea mays L.) plant fractions and across corn hybrid development periods. This research was conducted in 2007 and 2008 to evaluate the partitioning of secondary and micronutrients across vegetative and reproductive stages at the plant-fraction level for 1960- and 2000-era hybrids. Two popular hybrids for each era were grown, with measurement of nutrient concentration and content in several plant and grain fractions. Secondary and micronutrient concentrations in plant fractions were lower in 2000- than 1960-era hybrids with most nutrients, except ear shoots and tassels for certain nutrients. However, nutrient content was consistently greater in 2000-compared to 1960-era hybrids in the whole plant and fractions at most development stages, except tassels and ear shoots. In tassels, nutrient content was mostly smaller in 2000-era hybrids, but in ear shoots content was similar. The accumulation rates of most nutrients per growing degree day (GDD) were greater in the reproductive period for 2000-era hybrids, but similar among eras in the vegetative period. Remobilized nutrients from vegetative to reproductive components were similar between era hybrids, except Ca and Fe, and positive except Fe, Mn, and B. It is apparent that greater nutrient content in newer hybrids was driven mainly by associated nutrient uptake rates and greater dry matter (DM). Despite the greater nutrient content with the modern hybrids, removal with grain or stover harvest would still be small for S and micronutrients.

Thermal time (TT) is an agro‐climate index widely established and used in predicting plant development based on temperature. This index is a powerful tool for measuring multi‐faceted changes in temperature occurring from climate change. In the present study, TT was calculated for the entire frost‐free period and individual spring, summer, and fall seasons using growing degree day (GDD), general thermal index (GTI), crop heat unit (CHU), and heat stress degree day (HSDD) models for 1054 counties across 12 Midwest states on a daily basis from 1950 to 2017. The temporal trend for each county was fit with a linear regression model for percent change per year. During the frost‐free period, warming occurred in 260 to 489 counties with 0.06 to 0.34% gain per year dependent on model and county selected. Warming has occurred in northern and eastern counties primarily from gains in the fall season and partially from the spring. These TT gains are from additional calendar days from an expanded frost‐free period and secondarily from a change in maximum temperature (fall only). Heat stress (>30°C) during the frost‐free period has decreased for 212 counties in the west‐central region. Overall, the CHU model detected the most counties warming and had the lowest error particularly compared to the GDD model. Compared to 1950, some counties showed up to 1.2‐fold increase in frost‐free TT and are projected to 1.8‐fold by end of the 21st century. Current warming trends are related to projected TT trends such that adaptation planning can be guided by the trajectory from the past 68 yr. Core Ideas Northern and eastern counties in the Midwest have up to 1.2‐fold increase in frost‐free thermal time since 1950 while central and southern counties do not. The growing degree day model results in fewer counties detected and lower rates of warming compared to the general thermal index and crop heat unit models. The gain in thermal time is primarily from the fall season and secondarily from the spring.

As corn (Zea mays L.) hybrids change over time, and with increased use of different plant components for feed, bedding, and energy production, it is important to know macronutrient distribution within plants and how nutrient concentration and accumulation varies during plant development. This field study was conducted in 2007 and 2008 to evaluate dry matter (DM) biomass, macronutrient concentration, and macronutrient content in corn plant fractions (stalk, leaf, tassel, ear shoot, cob, and grain) across developmental stages with two hybrids from 1960 and 2000 eras. Concentrations of N, P, and K were generally lower in all plant fractions for the 2000 compared to 1960 era hybrids, except P concentration in stalks and grain and K concentration in leaves and ear shoots. In contrast, N, P, and K content was consistently higher in 2000 era hybrids for whole plants, leaves, and grain; a reflection of greater DM production. Nitrogen, P, K, and DM content in tassels was lower for 2000 than 1960 era hybrids. From the 1960s to 2000s, hybrid development brought about an increase in plant biomass and grain yield resulting in greater total nutrient content. However, macronutrient concentrations in vegetative plant fractions and grain decreased, thus moderating increase in plant total and grain nutrient content. This research shows the importance for analysis of newer hybrid vegetative and grain biomass on an ongoing basis to provide reliable estimates of macronutrient uptake patterns and removal with harvest of specific vegetative material and grain.

The future of agriculture will depend on how well we negotiate change and adapt. A changing climate is one of many drivers of change. Increased variability in distribution and timing of precipitation, along with changing temperatures, bring about greater volatility in global agricultural production and markets. Growing competition for water resources and increased water pollutants are altering the hydrology, biology, and chemistry of streams, lakes, and rivers. Concurrently, long-term productivity of agricultural lands is reduced in many row crop fields due to soil erosion, compaction, and nutrient depletion. Each growing season, a series of invasive species, diseases, and pests challenge the practices put in place to control them, requiring ever more intensive management by farmers. End users and consumers will continue to demand efficient and economical production while desiring more varied and resource-intensive diets, biofuel feedstocks, and food security as populations grow and developing countries gain wealth (Garnett et al. 2013; Bennett et al. 2014).

Core Ideas Evaluating corn dry matter and macronutrient accumulation patterns across era hybrids is necessary to understand changes in plant nutrient requirements and effects on accumulation timing and fertilization management. Era hybrids differed in dry matter and nutrient accumulation, with differences in nutrient content mainly related to dry matter production. Dry matter and P accumulation was linear, however, N and K accumulation slowed during the reproductive stages. Although the absolute dry matter production and nutrient content was greater with the most recent hybrids, relative to the maximum dry matter and N, P, and K content and the accumulation rate (cumulative growing degree unit‐based) remained the same across era hybrids. Results indicate that overall dry matter production and yield potential has been mainly responsible for changes in corn macronutrient requirements with development of new hybrids. Evaluating corn ( Zea mays L.) aboveground dry matter (DM) and macronutrient accumulation patterns across era hybrids is necessary to understand changes in plant nutrient requirements and effects on accumulation timing and fertilization management. Two popular hybrids for each of five era‐decades from 1960 to 2000 were grown in 2007 and 2008. Whole plant samples were collected at 10 development stages, with dry matter (DM), N, P, and K determined. Era hybrids differed in DM and nutrient accumulation, with differences in nutrient content mainly related to DM production. The 1960 to 1990 era hybrids were more similar in DM and nutrient content across development stages compared to the 2000 era hybrids which had the greatest content. Dry matter and P accumulation was linear (V6–R5 stages), however, N and K accumulation slowed during the reproductive stages. While the fraction of maximum plant content at R1 averaged 48, 71, 58, and 83% across hybrids for DM, N, P, and K, respectively; the ranges were 43 to 52% for DM (1990 and 1960), 64 to 78% for N (1990 and 1960), 55 to 60% for P (2000 and1960), and 69 to 93% for K (1990 and 1960). Although the absolute DM production and nutrient content was greater with the most recent hybrids, relative to the maximum DM, N, P, and K content and the accumulation rate, growing degree unit based, remained the same across era hybrids. This indicates that overall DM production and yield potential has been mainly responsible for changes in corn macronutrient requirements with development of new hybrids.

Core Ideas Three distinct site‐groupings resulted, with different recommended planting windows. Two planting windows were developed for each site‐grouping: 98–100% grain yield or 95–100% grain yield. The north‐central and northeast grouping had the earliest recommended planting window to maximize grain yield. Farmers use a suite of management practices to optimize corn (Zea mays L.) grain yield, including planting at appropriate times for their location. Research on planting dates across the years has tended to use categorical analysis and determination of recommendations by identifying a particular calendar date as optimum and setting yield decline relative to that. This approach was suitable given the experimental designs and number of sites available for analyses. An 18 site‐year Iowa dataset, however, that was constructed with planting dates on a sliding scale allowed regression analysis to be used instead of categorical analysis. This approach resulted in the construction of planting‐date recommendations as a window of time. Three distinct site‐groupings resulted for Iowa, which is different than previous statewide research: north‐central (NC) and northeast (NE); northwest (NW) and central (C); and southwest (SW) and southeast (SE). Two planting windows were developed for each site‐group based on the maximum yield on the response curve and a subtraction of 2 or 5% relative yield to develop yield windows of 98–100% or 95–100%, respectively. The response curves for each site‐grouping identify locations that exhibit a stronger grain‐yield response to planting date, especially in the northern and southern locations. The NC–NE grouping had the earliest 98–100% planting window (12–30 April) whereas the NW–C grouping (15 April–9 May) and SW–SE grouping (17 April–8 May) were later.

Two maize lines grown in Iowa with planting dates between early to mid-April and late May to June in 2008 and 2009 were used to examine how planting date of maize affects kernel characteristics. Planting the maize lines in late May and June (after optimum planting period) resulted in smaller granular-sizes and amylose contents of starch for both lines but larger proportions of short amylopectin branch-chains for the 37Y14 maize and no change to the length of the B73 amylopectin. Gelatinization and pasting properties did not consistently change with planting dates and their response varied across maize lines and planting years. Enzymatic hydrolysis rates of the starches increased with later planting dates. The ethanol yield calculated on a dry-kernel-mass basis was not significantly affected by maize planting dates, whereas the ethanol yield per unit of maize-planting area decreased with plantings done in late May and June because of reduced grain yield inherent with late plantings.

Drained lands, which include some of the most productive lands in the world, can experience both water excess and water deficit within a year. Storing drained water within the landscape could increase the sustainability of water for agriculture, particularly as intense rainfall and prolonged summer drought continue to increase under future climate change. A team of researchers and extension specialists from nine states are currently working towards a vision of transforming the process of designing and implementing agricultural drainage to include storage through the use of controlled drainage, saturated buffers, and drainage water recycling (i.e. capture, storage, and reuse). Field research data from experimental drainage sites from across the U.S. Corn Belt have been brought together in a database to support synthesis and modeling to determine economic and environmental impacts of drainage water storage. Results from this effort will extend the strategies and tools to agricultural producers, the drainage industry, watershed managers, agencies, and policy makers, and educate the next generation of engineers and scientists to design drainage systems that include water storage in the landscape.

Corn ( Zea mays L.) N use is of continued interest due to agronomic performance and environmental issues. This 2‐yr study evaluated era hybrid response to fertilizer nitrogen (FN) rate in a factorial arrangement of one popular hybrid per five decades (1960–2000 eras) and five N rates (0–224 kg N ha −1 ). An additional hybrid per era was grown at 168 kg N ha −1 . Hybrid productivity and nitrogen use efficiency (NUE) increased across the eras, but not between the 1980 and 1990 eras. Grain yield (GY) increased 65% and total plant biomass 43%, however, total plant nitrogen uptake (PNU) increased only 19% and across N rates was only higher for the 2000 era. At the agronomic optimum nitrogen rate (AONR), there was a linear GY increase of 0.13 Mg ha −1 yr −1 and GY N response of 0.091 Mg ha −1 yr −1 , indicating considerable genetic gain. There was no trend in AONR across eras. For plant N status measures, SPAD readings decreased and canopy index values increased across eras. All NUE measures indicated significant improvement in NUE. The apparent nitrogen recovery efficiency (NRE) at N rates near the AONR of each era, however, was not highest for the most recent eras. Harvest index (HI), grain nitrogen harvest index (GNHI), and fraction of total PNU accumulated by R1 were the same among eras. The grain nitrogen concentration (GNC), however, was 24% lower for the 2000 compared to the 1960 era. Corn hybrid development across the 50‐yr period improved productivity and NUE, but not the AONR.