Continuous Corn Research Articles

Tillage and crop succession effects on soil microbial metabolic activity and carbon utilization in a clay loam soil

Soil microorganisms play important roles in nutrient cycling and ecosystem functioning. Knowledge on the responses of soil microbial metabolic characteristics to agricultural practices is critical to better understand soil microbial processes in agroecosystems. The study aimed to explore the responses of soil microbial metabolic activities and their carbon utilization under different tillage and crop succession systems in a 12-year field experiment in a clay loam soil of Jilin Province, China. This experiment was set up in a split-plot design with four replicates including no-tillage (NT) and conventional tillage (CT) as main plots and continuous corn (CC) and corn-soybean succession (CS) treatments as subplots. Soil samples were collected from 0 to 5 cm and 5–15 cm depths. The results showed that compared with CT, NT increased soil organic carbon, soil microbial biomass carbon, basal respiration and microbial coefficient at 0–5 cm depth. Greater basal respiration was observed under CC than under CS at both depths. Compared with NTCC, NTCS decreased microbial functional diversity at 0–5 cm depth and increased microbial metabolic quotient at 5–15 cm depth. Redundancy analysis indicated that crop succession management induced the changes in soil microbial carbon utilization. Compared with other soil environmental factors, NO3−-N and soil moisture significantly affected soil microbial metabolic activities. No significant correlation was found between microbial carbohydrate utilization and soil organic carbon in this study. Structural equation modeling analysis suggested that corn-soybean succession practice could stimulate the consumption of aromatic acids, which indirectly affected the accumulation of soil organic carbon.

Perennialization and Cover Cropping Mitigate Soil Carbon Loss from Residue Harvesting.

While the US Midwest is expected to serve as a primary feedstock source for cellulosic biofuel production, the impacts of residue harvesting on soil organic carbon (SOC) may greatly limit sustainable production capacity. However, viable feedstock production could be realized through adoption of management practices and cropping systems that offset residue-harvest-induced SOC losses. Sequestration of SOC can be enhanced by increasing the duration of crop soil cover through cover or double cropping or cultivation of dedicated perennials. However, assessing the efficacy of such options across sites and over long periods is experimentally challenging. Hence, we use the Environmental Productivity Integrated Climate (EPIC) model to provide such an assessment. Model-data integration was used to calibrate and evaluate model suitability, which exhibited reasonable effectiveness through of 0.97 and 0.63 for SOC stock and yield, respectively. Long-term simulations indicate considerable capacity for offsetting SOC loss. Incorporating rye ( L.) into continuous corn ( L.) and corn-soybean [ (L.) Merr.] systems offset the SOC losses induced by harvesting 21.2 and 38.3% of available stover, respectively. Similarly, converting 20.4% of corn-soybean land to miscanthus ( × J.M. Greef & Deuter ex Hodkinson & Renvoize) or 27.5% of land to switchgrass ( L.) offset the SOC impacts of harvesting 60% of stover from the remaining corn-soybean lands. These responses indicate that adoption of such measures would sizably affect the life cycle consequences of residue-derived biofuels and expand estimates of sustainable cellulosic feedstock production capacity from the US Midwest.

Soil Carbon Response to Projected Climate Change in the US Western Corn Belt.

The western US Corn Belt is projected to experience major changes in growing conditions due to climate change over the next 50 to 100 yr. Projected changes include increases in growing season length, number of high temperature stress days and warm nights, and precipitation, with more heavy rainfall events. The impact these changes will have on soil organic carbon (SOC) needs to be estimated and adaptive changes in management developed to sustain soil health and system services. The process-based model CQESTR was used to model changes in SOC stocks (0-30 cm) of continuous corn ( L.) and a corn-soybean [ (L.) Merr.] rotation under disk, chisel, ridge, and no-tillage using projected growing season conditions for the next 50 yr. Input for the model was based on management and harvest records from a long-term tillage study (1986-2015) in eastern Nebraska, and model output was validated using measured changes in SOC from 1999 to 2011 in the study. The validated model was used to estimate changes in SOC over 17 yr under climatic conditions projected for 2065 under two scenarios: (i) crop yields increasing at the observed rate from 1971 to 2016 or (ii) crop yields reduced due to negative effects of increasing temperature. CQESTR estimates of SOC agreed well with measured SOC ( = 0.70, < 0.0001). Validated model simulated changes in SOC under projected climate change differed among the three soil depths (0-7.5, 7.5-15, and 15-30 cm). Summed over the 0- to 30-cm depth, there were significant three-way interactions of year × rotation × yield ( = 0.014) and year × tillage × yield ( < 0.001). As yield increased, SOC increased under no-tillage continuous corn but was unchanged under no-tillage corn-soybean and ridge tillage regardless of cropping system. Under chisel and disk tillage, SOC declined regardless of cropping system. With declining yields SOC decreased regardless of tillage or cropping system. These results highlight the interaction between genetics and management in maintaining yield trends and soil C.

Short Corn Rotations Do Not Improve Soil Quality, Compared with Corn Monocultures

Compared corn–corn–corn vs. corn–corn–soybean vs. corn–soybean rotations on their effects on soil properties after 12 yr. Locations were correctly identified by canonical discriminant analyses (CDA) rules based on measured soil properties. Regardless of location, soil attributes did not differ under short corn rotations and corn–corn–corn systems. Soil attributes contrasted most between corn and soybean phases of the corn–soybean rotation. Short‐duration summer annual crop rotations are widely used in the Midwest, but their long‐term impact on soil quality has not been thoroughly examined. Our goal was to compare soil properties under long‐term use of the most common crop rotations around Illinois, and to identify soil quality indicators for rotations in the state. Crop rotations of continuous corn (Zea mays L.) (CCC), corn–soybean [Glycine max (L.) Merr.] (CS), and corn–corn–soybean (CCS) were arranged in a randomized complete block design (RCBD), with three or four replications at each of six locations, with all phases present each year for 12 yr. We measured 21 soil properties on the surface soil and 18 properties at four successive depths, rendering a total of 126 and 504 observations available for the multivariate statistical analyses, including principal component analyses (PCA) and canonical discriminant analysis (CDA) in both data sets. We found that our discriminant rules based on the measured soil properties correctly identified the location of origin of the soil samples in 98% of cases, representing &lt;2% error rates for the cross‐validation results at each location. Crop rotations, on the other hand, did not affect any of the soil properties evaluated, results further confirmed by our CDA analyses that showed high error rates for classification. Though these short corn rotations make economic sense, they behave similarly to corn monocultures from the soil quality standpoint, compromising the sustainability of our current agricultural systems and highlighting the need to increase temporal and spatial diversification.

A Modeling Framework to Evaluate the Impacts of Future Climate on Soil Organic Carbon Dynamics.

Soil organic C (SOC) is significantly affected by changes in climate that control the physical, chemical, and biological processes in the soil. Simulating the impacts of future climate on SOC is challenging due to the limited availability of soil and climate variables required to properly simulate future SOC dynamics. The main objective of this study was to develop a modeling framework to quantify the impacts of future climate on SOC dynamics. The framework was developed for the Model for Nitrogen and Carbon in Agro-Ecosystems (MONICA) using the data collected from three University of Illinois Crop Science Research Centers. Projected precipitation and air temperature, collected from 32 global circulation models, were used to estimate the climate variables and cropping operation schedules required as inputs in MONICA. Six corn ()-soybean [ (L.) Merr.] rotation scenarios were considered in the simulations. Results showed that the total SOC in the upper 30 cm of the soil was expected to decrease from 43 to 70% in 2015 to 2075, with an uncertainty range of 13 to 16% due to the variation in climate prediction. The SOC in corn-soybean rotation schemes did not vary significantly from that of continuous corn scheme. The ability of a model to simulate realistic results depends significantly on the reliability of input data used to parameterize the model. A methodology that comprehensively estimates the impacts of future climatic conditions on SOC allows for realistic model results that can be used as a basis for environmental options, leading to a sustainable agro-production system.

Legacy effects of land use on soil nitrous oxide emissions in annual crop and perennial grassland ecosystems

Land use conversions into and out of agriculture may influence soil-atmosphere greenhouse gas fluxes for many years. We tested the legacy effects of land use on cumulative soil nitrous oxide (N2 O) fluxes for 5yr following conversion of 22-yr-old Conservation Reserve Program (CRP) grasslands and conventionally tilled agricultural fields (AGR) to continuous no-till corn, switchgrass, and restored prairie. An unconverted CRP field served as a reference. We assessed the labile soil C pool of the upper 10cm in 2009 (the conversion year) and in 2014 using short-term soil incubations. We also measured insitu soil N2 O fluxes biweekly from 2009 through 2014 using static chambers except when soils were frozen. The labile C pool was approximately twofold higher in soils previously in CRP than in those formerly in tilled cropland. Five-year cumulative soil N2 O emissions were approximately threefold higher in the corn system on former CRP than on former cropland despite similar fertilization rates (~184kg N·ha-1 ·yr-1 ). The lower cumulative emissions from corn on former cropland were similar to emissions from switchgrass that was fertilized less (~57kg N·ha-1 ·yr-1 ), regardless of former land use, and lowest emissions were observed from the unfertilized restored prairie and reference systems. Findings support the hypothesis that soil labile carbon levels modulate the response of soil N2 O emissions to nitrogen inputs, with soils higher in labile carbon but otherwise similar, in this case reflecting land use history, responding more strongly to added nitrogen.

No-till and cropping system diversification improve soil health and crop yield

The performance of no-till (NT) in temperate regions may be enhanced through the integration of additional conservation practices such as cover cropping and crop rotations. This study assessed the long-term impacts of continuous (20+ years) NT in comparison to plow-till (PT) management on soil properties and corn (Zea mays L.) yields in New York. The effects of tillage were assessed in combination with different cropping systems (24 years corn monoculture vs. 12 years corn monoculture; and with or without interseeded cover crops) on three soil textures: clay loam, loamy sand and silt loam. We measured four soil biological indicators - organic matter (OM), active carbon (ActC), respiration (Resp) and protein (Prot); four soil physical indicators - available water capacity (AWC), water stable aggregation (WSA), penetration resistance (PR) and water infiltration rate (InfRate); soil chemical indicators (plant available nutrients, pH and total N), and corn yield. Soil managed under long-term NT showed the most favorable soil biological, physical and chemical conditions for plant development, with higher levels of OM, Prot, Resp, WAS, total N, P and Zn, and InfRate. Benefits of introducing a grass-legume cover crop mixture into the cropping system were evident after 4 years for OM, Prot, Resp, AWC, Fe and Zn. Cover crop effects were greater under NT than PT, and additive to the NT benefits. On the clay loam soil, the effects of a 6-year interruption of continuous corn production with a perennial grass crop were still discernable with several soil health indicators 12 years after resuming corn production under NT. The better soil conditions under NT resulted in higher corn yields in both the loamy sand and silt loam soils, but not the clay loam. Our study shows that long-term NT can be viable in temperate regions, promoting significant improvement in soil health and crop yield and that these benefits are enhanced when NT is combined with crop rotation (perennial grass) and cover crops.

Exploring the Relationships between Greenhouse Gas Emissions, Yields, and Soil Properties in Cropping Systems

Relationships between greenhouse gas emissions, yields, and soil properties are not well known. Utilizing two datasets from long-term cropping systems in Illinois, USA, our we aim to address these knowledge gaps. The objective of this study was to explore the relationships between the physical and chemical properties and greenhouse gas (GHG) emissions of soil, and cash crop yields over a four-year time-period and following 15 years of treatment implementation in Illinois, USA. The experimental layout was a split-plot arrangement involving rotation and tillage treatments in a randomized complete block design with four replications. The studied crop rotations were continuous corn [Zea mays L.] (CCC), corn-soybean [Glycine max (L.) Merr.] (CS), continuous soybean (SSS), and corn-soybean-wheat [Triticum aestivum L.] (CSW), with each phase being present for every year. The tillage options were chisel tillage (T) and no-tillage (NT). We used an array of multivariate approaches to analyze both of our datasets that included 31 soil properties, GHG emissions (N2O, CO2, and CH4) and cash crop yields. The results from our analyses indicate that N2O emissions are associated with a low soil pH, an increased Al concentration, the presence of soil nitrate throughout the growing season, an increase in plant available water (PAW) and an increased soil C concentration. Likewise, soil CO2 respiration was correlated with low pH, elevated Al concentrations, low Ca, increased PAW, higher levels of microbial biomass carbon (MBC), and lower water aggregate stability (WAS). Emissions of CH4 were associated with increased levels of MBC. Lastly, the yield index (YdI) was correlated with lower levels of soil Ca and available P and lower values of WAS. The association between high YdI and lower WAS can be attributed to tillage, as tillage lowers WAS, but increases yields in highly productive cropping systems in the Midwest.

A Systems Modeling Approach to Forecast Corn Economic Optimum Nitrogen Rate.

Historically crop models have been used to evaluate crop yield responses to nitrogen (N) rates after harvest when it is too late for the farmers to make in-season adjustments. We hypothesize that the use of a crop model as an in-season forecast tool will improve current N decision-making. To explore this, we used the Agricultural Production Systems sIMulator (APSIM) calibrated with long-term experimental data for central Iowa, USA (16-years in continuous corn and 15-years in soybean-corn rotation) combined with actual weather data up to a specific crop stage and historical weather data thereafter. The objectives were to: (1) evaluate the accuracy and uncertainty of corn yield and economic optimum N rate (EONR) predictions at four forecast times (planting time, 6th and 12th leaf, and silking phenological stages); (2) determine whether the use of analogous historical weather years based on precipitation and temperature patterns as opposed to using a 35-year dataset could improve the accuracy of the forecast; and (3) quantify the value added by the crop model in predicting annual EONR and yields using the site-mean EONR and the yield at the EONR to benchmark predicted values. Results indicated that the mean corn yield predictions at planting time (R2 = 0.77) using 35-years of historical weather was close to the observed and predicted yield at maturity (R2 = 0.81). Across all forecasting times, the EONR predictions were more accurate in corn-corn than soybean-corn rotation (relative root mean square error, RRMSE, of 25 vs. 45%, respectively). At planting time, the APSIM model predicted the direction of optimum N rates (above, below or at average site-mean EONR) in 62% of the cases examined (n = 31) with an average error range of ±38 kg N ha−1 (22% of the average N rate). Across all forecast times, prediction error of EONR was about three times higher than yield predictions. The use of the 35-year weather record was better than using selected historical weather years to forecast (RRMSE was on average 3% lower). Overall, the proposed approach of using the crop model as a forecasting tool could improve year-to-year predictability of corn yields and optimum N rates. Further improvements in modeling and set-up protocols are needed toward more accurate forecast, especially for extreme weather years with the most significant economic and environmental cost.

Long-term crop rotation and tillage effects on soil greenhouse gas emissions and crop production in Illinois, USA

Two of the most important agricultural practices aimed at improving soil properties are crop rotations and no-tillage, yet relatively few studies have assessed their long-term impacts on crop yields and soil greenhouse gas (GHG) emissions. The objective of this study was to determine the influence of tillage and crop rotation on soil GHG emissions and yields following 15 years of treatment implementation in a long-term cropping systems experiment in Illinois, USA. The experimental design was a split-plot RCBD with crop rotation as the main plot: (continuous corn [Zea mays L.] (CCC), corn-soybean [Glycine max (L.) Merr.] (CS), continuous soybean (SSS), and corn-soybean-wheat [Triticum aestivum L.] (CSW); with each phase of each crop rotation present every year) and tillage as the subplot: chisel tillage (T) and no-tillage (NT). Tillage increased the yields of corn and soybean. Tillage and crop rotation had no effect on methane (CH4) emissions (p = 0.4738 and p = 0.8494 respectively) and only rotation had an effect on cumulative carbon dioxide (CO2) (p = 0.0137). However, their interaction affected cumulative nitrous oxide (N2O) emissions significantly (p = 0.0960); N2O emissions from tilled CCC were the greatest at 6.9 kg-N ha−1-yr−1; while emissions from NT CCC (4.0 kg-N ha−1-yr−1) were not different than both T CS or NT CS (3.6 and 3.3 kg-N ha−1−yr−1, respectively). Utilizing just a CS crop rotation increased corn yields by around 20% while reducing N2O emissions by around 35%; soybean yields were 7% greater and N2O emissions were not affected. Therefore results from this long-term study indicate that a CS rotation has the ability to increase yields and reduce GHG emissions compared to either CCC or SSS alone, yet moving to a CSW rotation did not further increase yields or reduce N2O emissions.

Carbon and Nitrogen Content of Soil Organic Matter and Microbial Biomass under Long-Term Crop Rotation and Tillage in Illinois, USA

Crop rotation and tillage alter soil organic matter (SOM) dynamics by influencing the soil environment and microbes carrying out C and N cycling. Our goal was to evaluate the effect of long-term crop rotation and tillage on the quantity of C and N stored in SOM and microbial biomass. Two experimental sites were used to evaluate four rotations—continuous corn (Zea mays L.) (CCC), corn-soybean (Glycine max [L.] Merr.) (CS), corn-soybean-wheat (Triticum aestivum L.) (CSW), and continuous soybean (SSS), each split into chisel tillage (CT) and no-till (NT) subplots. The CSW rotation increased soil organic carbon (SOC) content compared to SSS; SSS also reduced total nitrogen (TN) compared to other rotations. Levels of SOC and TN were 7% and 9% greater under NT than CT, respectively. Rotation did not affect microbial biomass C and N (MBC, MBN) while tillage reduced only MBN at 10–20 cm compared to NT, likely related to dispersion of N fertilizers throughout the soil. Despite the apparent lack of sensitivity of microbial biomass, changes in SOC and TN illustrate the effects of rotation and tillage on SOM dynamics. The inclusion of crops with high C: N residues and no-till use both support higher C and N content in the top 20 cm of the soil.

Ecosystem carbon exchange on conversion of Conservation Reserve Program grasslands to annual and perennial cropping systems

Land use changes into and out of agricultural production may substantially influence ecosystem carbon (C) balance for many years. We examined ecosystem C balances for eight years after the conversion of 22 year-old Conservation Reserve Program (CRP) grasslands and formerly tilled agricultural fields (AGR) to annual (continuous no-till corn) and perennial (switchgrass and restored prairie) cropland. An unconverted CRP field (CRP-Ref) was maintained as a historical reference. Ecosystem C balance was assessed using adjusted net ecosystem carbon exchange (NEEadj) calculated by adding C removed in harvested biomass to NEE measured using eddy covariance method. The cumulative NEEadj of the corn and perennial systems on former CRP fields showed that these systems were a net C source to the atmosphere over the 8-year period while on former AGR fields, the perennial systems were net C sinks and the corn system near-neutral. The CRP-Ref was near neutral until a drought year when it became a net source. The corn system on the CRP field will likely reach a new lower soil C equilibrium at least 14 years after conversion but will never regain the C lost upon conversion under current no-till management with residue partially removed. On the other hand, the perennial systems could fully regain in ∼14 years the C lost following conversion. The cumulative NEEadj of the corn systems exhibited a higher C emission than did the perennial systems within the same land use histories, reflecting the dominant role of crop type and management in agricultural ecosystem C balance. Results suggest that converting croplands to grasslands results in immediate C gains whereas converting grasslands to croplands results in permanent (no-till corn with partial residue removal) or temporary (perennial herbaceous crops) net C loss to the atmosphere. This has a significant implications for global climate change mitigation where biomass production from annual and perennial crops is promoted to avoid fossil-fuel C emissions (biofuel) or to remove CO2 from the atmosphere (bioenergy C capture and storage).

Early accumulation of active fraction soil carbon in newly established cellulosic biofuel systems

We examined relative changes in soil C pools shortly after the establishment of six perennial and two annual bioenergy cropping systems that differed in diversity (monoculture vs. polyculture). Perennial systems included two monocultures (switchgrass, Panicum virgatum; and miscanthus, Miscanthus×giganteus) and four polycultures including hybrid poplar (Populus sp.)+herbaceous understory; mixed native grasses, successional vegetation, and restored prairie. Two annual systems included no-till continuous corn (Zea mays) and rotational corn (corn-soybean (Glycine max)-canola (Brassica napus)). Each crop was planted in a full factorial design at both a moderate fertility Alfisol and a high fertility Mollisol site. Relative differences in active, slow, and passive C pools in surface soils, where C changes are most likely to be detected early, were evaluated with 322-day laboratory incubations followed by acid hydrolysis to infer different pools from exponential decay curves. Five years post-establishment, active C pools under perennial polycultures at the Alfisol site were up to twice those under annual and perennial monocultures, and followed the order hybrid poplars (696±216μgCg−1 soil, n=5 replicate blocks)≈native grasses (656±155)≈restored prairie (638±44)>early successional (500±54)≫continuous corn (237±68)≈rotational corn (180±n.a.). Active C pools in perennial monocultures were similar to those in continuous corn: switchgrass (274±29)≈miscanthus (299±9). In contrast, differences in active C pools among crops at the more fertile Mollisol site were not detectable except for greater pools in the restored prairie and rotational corn systems. At both sites, slow and passive C pools differed little among systems except that slow pools were greater in the poplar system. That diversity rather than perenniality itself led to greater active C pools suggests that polycultures might be used to accelerate soil C accumulation in bioenergy and other perennial cropping systems.

The influence of crop rotation on corn total biomass production

Agriculture in the Midwest region of the United States is based on intensive corn (Zea mays L.) production that provides food, feed, and fuel. Crop rotation is a vital management option for improved yield and environment preservation. Three rotation systems—continuous corn (CC), corn–soybean (Glycine max [L.] Merr.; CS), and corn–soybean–wheat (Triticum aestivum L.; CSW)—were selected to study their effects on grain yields and carbon (C) and nitrogen (N) accumulation and partitioning within corn grain, stover, and cob plant components. The experiment was conducted at three pre-established crop rotation experiments located at three sites in Wisconsin. Biomass sampling was performed in four consecutive years (2011 to 2014). Analysis of variance showed differences in location for most variables, an effect of crop rotation on stover biomass and stover C, and an interaction effect between location and rotation on soybean grain yield. Averaged across years and locations, final corn and soybean grain yield increased with rotation complexity where corn in the CSW rotation had 15% and 8% greater yield than CC and CS rotation, respectively. Overall, the biomass distribution among corn plant parts was 52%, 41%, and 7% for grain, stover, and cob, respectively. Stover and cobs harvested from corn grown in monoculture produced approximately 11% (0.54 Mg C ha−1) less C than corn grown in either CS or CSW rotation. Across rotations, the accumulation of N in plant tissues was not significantly different. However, these results show that crop rotation can increase grain yield and biomass C and partially offset the difference in soil C, which is expected to be greater under CC.

Economic Performance of Crop Rotations in the Presence of Herbicide‐Resistant Giant Ragweed

Core Ideas Crop rotations containing alfalfa produced the greatest economic net return.Crop rotations with alfalfa stochastically dominated all other crop rotations.Alfalfa improves control of herbicide‐resistant giant ragweed while providing substantial economic net return. Economic assessment of alternative crops and crop rotations helps farmers determine those most appropriate for their farms. The objective of this research was to evaluate the economic net return and associated financial risk for crops and crop rotations common to the midwestern United States, based on two 3‐yr experiments in southern Minnesota where herbicide‐resistant giant ragweed (Ambrosia trifida L.) was present. Crop rotations included corn (Zea mays L.), soybean [Glycine max L. (Merr.)], wheat (Triticum aestivum L.), and alfalfa (Medicago sativa L.). Crop rotations were continuous corn (CCC), soybean–corn–corn (SCC), corn–soybean–corn (CSC), soybean–wheat–corn (SWC), soybean–alfalfa–corn (SAC), and alfalfa–alfalfa–corn (AAC). Average crop yields during the study period were utilized along with average prices received and estimated production costs for each crop in Minnesota during this period to evaluate economic net return. Average net return of the SWC, SCC, CCC, CSC, SAC, and AAC rotations was US$11, $170, $247, $258, $368, and $919 ha–1 yr–1, respectively. The AAC rotation was stochastically dominant to all other crop rotations for risk‐averse decision makers. One or 2 yr of alfalfa stochastically dominated corn, soybean, and wheat, regardless of crop rotation, largely due to more stable alfalfa prices over the study period coupled with above‐average yield and lower production costs. These results confirm that rotations containing alfalfa have the potential to provide a substantial economic net return to farmers while mitigating the risk of herbicide‐resistant giant ragweed (Ambrosia trifida L.) infestations.

Ten‐Year Assessment Encourages No‐Till for Corn Grain and Stover Harvest

Core Ideas No‐till with 35% stover removal met corn grain yield, income, and soil protection goals. Profitability for no‐till and chisel plow systems were equal due to lower machinery costs. Cost‐efficient stover harvest is essential for bio‐economy development. Developing a bio‐economy by harvesting crop residues from highly productive corn (Zea mays L.) cropping systems requires science‐based management decisions to maintain or enhance grain yield and soil, water, and air resources. Which tillage and stover harvest practices are best for accomplishing these goals? Continuous corn grain yield response to either no‐till or chisel plowing with two stover harvest rates (3.4 or 5.1 Mg ha−1 yr−1) was evaluated for 10 yr in central Iowa. Each tillage and stover removal combination was replicated four times. Year‐to‐year variation affected grain yield more than tillage practice (0.2 Mg ha−1) or stover removal (0.1 Mg ha−1). Grain yields were not statistically different (p = 0.33) between tillage systems. Including machinery costs made return on investment for chisel plow and no‐till equivalent even though no‐till yields were numerically lower. Net stover income per megagram was US$2 to $4 greater at the 3.4 versus 5.1 Mg ha−1 harvest rate because of more efficient harvesting. Among the four practices, no‐till with 3.4 Mg ha−1 stover harvest met multiple goals, including providing acceptable corn grain yields, positive net income per megagram stover, and sufficient residues to protect the soil.

In situ infiltration as influenced by cover crop and tillage management

Water is usually the most limiting factor in agricultural grain crop production. Various agricultural management practices, such as tillage and use of cover crops, have the potential to influence water infiltration into soil. This study was conducted on a Waldron silt loam (fine, smectitic, calcareous, mesic Aeric Fluvaquents) soil to evaluate the influence of cover crop and tillage management on in situ infiltration. The field site included three replicate blocks in a randomized complete block design with each plot measuring 21.3 m (69.9 ft) length and 12.2 m (40 ft) width. The two treatment factors included cover crop at two levels (cereal rye [Secale cereale] cover crop [CC] versus no cover crop [NC]) and tillage at two levels (moldboard plow tillage [Till] versus no-tillage [NT]). Continuous corn (Zea mays L.) was grown. Infiltration rates were measured in all the treatments using a Mariotte system with single-ring infiltrometers during the 2014 and 2015 growing seasons. Water infiltration parameters were estimated using the Parlange and Green-Ampt infiltration equations. Parlange and Green-Ampt models appeared to fit measured data well with coefficient of variation ranging from 0.92 to 0.99. In 2014, the saturated hydraulic conductivity (KS) parameter value determined from the Parlange model was 30.4 mm h−1 (1.2 in hr−1) for NT, about 42% greater than Till. The KS parameter value determined from the Green-Ampt model was 25.9 mm h−1 (1 in hr−1) for NT, about 54% greater than Till. In 2015, the sorptivity (S) parameter value determined from the Parlange model was 38.6 mm h−0.5 (1.5 in hr−0.5) for CC, about 82% greater than NC. The S parameter value determined from the Green-Ampt model was 34 mm h−0.5 (1.3 in hr−0.5) for CC, about 90% greater than NC. Cover crop management can increase water infiltration, which can improve soil quality and enhance the sustainability of crop production systems.

Corn Residue Baling and Grazing Impacts on Soil Carbon Stocks and Other Properties on a Haplustoll

Core Ideas Corn residue baling reduced SOC stocks by 2.16 Mg ha–1 yr–1 compared with no removal after 3 yr. Baling increased erosion potential and reduced soil microbial biomass. Cattle grazing of corn residues did not generally affect soil properties. Baling and grazing effects on soil properties did not vary with irrigation and tillage system. Baling affected soil properties more than grazing regardless of irrigation and tillage. Baling and grazing of corn (Zea mays L.) residues are common practices in irrigated systems to meet the increasing demand for forage. Our understanding of how such practices affect soil properties under different tillage and irrigation levels is, however, still limited. This study assessed the impacts of corn residue baling and grazing on soil organic C (SOC) stocks, particulate organic matter (POM) concentration, soil microbial communities, sorptivity, and wind and water erosion potential under continuous corn managed with two irrigation (full and limited) and two tillage (no‐till and strip till) levels after 3 yr on a silt loam in the central Great Plains. On average, residue removal was 66% for baling and 24% for grazing. Baling reduced SOC stocks by 2.16 Mg ha–1 yr–1 for the 0‐ to 20‐cm depth compared with no residue removal, but residue grazing, irrigation, and tillage had no effects. Full irrigation decreased mean weight diameter (MWD) of wet aggregates by 19% compared with limited irrigation, attributed to Na accumulation. No‐till had lower wind‐erodible fraction and greater microbial biomass than strip till. Regardless of irrigation and tillage, baling increased wind‐erodible fraction by 43% and decreased MWD by 56%, POM concentration by 41%, sorptivity by 57%, and microbial biomass in the upper 5‐cm depth compared with grazing and no residue removal. Grazing increased POM concentration and actinomycete biomass compared with no residue removal. Overall, changes in soil properties due to baling were larger and more rapid than in most previous studies, while grazing had fewer effects on soil properties.

Stability of Corn and Soybean Yield Ratios in Three Midwestern Environments

Core Ideas Corn/soybean yield ratios estimate species × environment interactions.County yields from Kentucky, Iowa, and Nebraska (1972–2015) were used.Cropping systems had a greater effect on average ratios than productivity level.Year‐to‐year variation in the ratio decreased as the productivity level increased.Yield ratios increased significantly in only 37% of the counties (mostly in Iowa) Developing cropping systems to maintain productivity in future environments will require a better understanding of crop species × environment interactions. The ratios of county corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] yields (corn/soybean) from three midwestern states (Kentucky [31 counties], Iowa [47 counties] and Nebraska [irrigated, 33 counties]) (1972 through 2015) were used to evaluate this interaction. Yield estimates (converted to a weight basis) were obtained from the National Agriculture Statistics Service. Average yield ratios were similar in Iowa (2.96) and Nebraska (3.00) in spite of higher yields in Nebraska. The highest average ratio (3.39) occurred in Kentucky counties where soybean double cropped after winter wheat (Triticum aestivium L.) predominated. Yield ratios were remarkably stable (low CVs) over time in high‐yield environments, but stability decreased as county productivity (estimated by average corn yield) decreased (CVs increased from ∼8 to 23%). The mean yield ratios in Kentucky and Nebraska decreased significantly as the proportion of continuous corn in a county increased. The largest yield ratios in non‐double crop counties in Kentucky were associated with a larger proportion of continuous soybean in the rotation. Yield ratios increased significantly (p &lt; 0.10) from 1972 to 2015 in only 37% of the counties (mostly in Iowa). The largest interactions between corn and soybean involved cropping systems and not fundamental physiological characteristics of these species. The consistency of mean yield ratios in rain fed and irrigated environments suggests that these crops may respond similarly to changes in precipitation.

Soil structural stability assessment with the fluidized bed, aggregate stability, and rainfall simulation on long-term tillage and crop rotation systems

The establishment of long-term tillage and crop rotations studies helps to investigate the cumulative effect and the long-term effect of management practices on soil properties, including those affecting soil health and water quality. In this study, a suite of techniques was used to evaluate the impact of a 28-year long-term tillage and crop rotations on soil structural stability parameters including soil cohesion, aggregate stability, and sediment loss. Fluidized bed experiments to estimate soil cohesion and aggregate stability tests were performed on samples collected from plots managed under chisel tillage (CT) and no-till practice (NT) and four rotations (continuous corn [Zea mays], CC; continuous soybean [Glycine max], BB; corn-soybean, CB; and soybean-corn, BC). At the same site, rainfall simulation experiments were conducted and sediment loss was correlated to fluidized bed and aggregate stability measurements. No-till practice had a positive effect on soil cohesion in the 0–15 cm soil layer; average pressure drop at fluidization (ΔPf) values were 30.8 Pa for NT and 17.0 Pa for CT and a higher proportion of stable macroaggregates was present under NT practice (51.4% vs. 28.9%). In the 15–30 cm soil layer, aggregate stability measurements mimicked those of the surface layer for each tillage practice and crop rotation. In this study, we found no correlation between fluidized bed results and aggregate stability tests. The soil organic carbon content correlated to macroaggregates (R2 = 0.56) and magnitude of cohesion (R2 = 0.51). Corn residues were associated with improved aggregation in both surface and lower soil layers with respectively 18% and 13% more aggregates than soybean residues. Rainfall simulation experiments conducted on the sample sites revealed tillage effect on sediment loss patterns consistent with aggregate stability and fluidized bed measurement results. Chisel-tilled fields yielded 20 times more sediment loss than no-till fields. The effect of corn residue on aggregate stability resulted in 380 and 6.7 kg ha−1 less sediment loss under conventional and no-till practices, respectively.