Matt Liebman

• Iowa State University

Diversified cropping systems offer a chance to mitigate environmental impacts of conventional agriculture, but effects on soil organic carbon (SOC) sequestration and nitrogen (N) dynamics remain debated. We integrated a 20-year field experiment and laboratory measurements with three stable-isotope-enabled mechanistic models to examine SOC stocks an...

Though corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] are widely grown and readily accepted into commodity markets and biofuel facilities, heavy reliance on seeds of those two crops for bioenergy production has been linked to environmental degradation, including nutrient discharge to water, and to constraints on food production. Alternativ...

Various soil health indicators that measure a chemically defined fraction of nitrogen (N) or a process related to N cycling have been proposed to quantify the potential to supply N to crops, a key soil function. We evaluated five N indicators (total soil N, autoclavable citrate extractable N, water-extractable organic N, potentially mineralizable N...

Various soil health indicators that measure a chemically defined fraction of nitrogen (N) or a process related to N cycling have been proposed to quantify the potential to supply N to crops, a key soil function. We evaluated five N indicators (total soil N, autoclavable citrate extractable N, water‐extractable organic N, potentially mineralizable N...

Aggregate stability is a commonly used indicator of soil health because improvements in aggregate stability are related to reduced erodibility and improved soil–water dynamics. During the past 80 to 90 years, numerous methods have been developed to assess aggregate stability. Limited comparisons among the methods have resulted in varied magnitudes...

Farmers, scientists, and other soil health stakeholders require interpretable indicators of soil hydraulic function. Determining which indicators to use has been difficult because of measurement disconformity, spatial and temporal variability, recently established treatments, and the effect of site characteristics on management practice differences...

Soil organic carbon (SOC) is closely tied to soil health. However, additional biological indicators may also provide insight about C dynamics and microbial activity. We used SOC and the other C indicators (potential C mineralization, permanganate oxidizable C, water extractable organic C, and ß-glucosidase enzyme activity) from the North American P...

Soil organic carbon (SOC) is closely tied to soil health. However, additional biological indicators may also provide insight about C dynamics and microbial activity. We used SOC and the other C indicators (potential C mineralization, permanganate oxidizable C, water extractable organic C, and β-glucosidase enzyme activity) from the North American P...

Corn- and soybean-dominated cropping systems create and maintain a favorable environment for summer annual weeds whose emergence and growth phenology are similar to these annual summer crops. Cropping system diversification can be an effective approach for controlling noxious weeds without increasing reliance on chemical herbicides. Diversification...

Weed communities in three cropping systems suitable for the Midwestern USA were studied from 2017 through 2020 to examine how crop diversification and the intensity of herbicide use affected weed community diversity, stand density, and aboveground mass. A baseline 2-year cropping system with corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) g...

Addition of an overwintering cereal rye (Secale cereale L.) cover crop (CC) to midwestern maize (Zea mays L.)‐based systems offers several environmental benefits, but the long‐term effects of this practice on soil hydrological properties are not well understood. We utilized four long‐term (10+ yr) trials (two commercial fields, two research plots)...

Conventional agriculture in the Midwest US lacks diversity, relies heavily on external inputs to maintain crop yields, and contributes to soil and water quality degradation. Using diverse crop rotations and incorporating livestock are promising solutions to these and other problems linked to current cropping systems dominated by maize (Zea mays L.)...

The world currently faces a suite of urgent challenges: environmental degradation, diminished biodiversity, climate change and persistent poverty and associated injustices. All of these challenges can be addressed to a large extent through agriculture. A dichotomy expressed as ‘food versus fuel’ has misled thinking and hindered needed action toward...

Cover cropping has been proposed as an important component of integrated weed management strategies due to its potential effects on multiple demographic processes, including weed seedling emergence from soil, plant survival, seed production, and seed predation. In this article, we report the results of modelling analyses that investigated how a cov...

The highly specialized maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] production system that dominates midwestern U.S. agriculture has led to widespread on‐farm and off‐farm degradation of and damage to natural resources. The practice of extending maize–soybean rotations with small grains and forages has great potential to balance product...

Storkey and Neve (2018) hypothesised that weed seedbank diversity could be used as an indicator of agroecosystem sustainability, with cropping systems associated with higher weed seedbank diversity being more agronomically and environmentally sustainable than those with lower weed diversity. We evaluated their hypothesis using multiple years of emp...

Cool-season cover crops have been shown to reduce soil erosion and nutrient discharge from maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] production systems. However, their effects on long-term weed dynamics are not well-understood. We utilized five long-term research trials in Iowa to quantify germinable weed seedbank densities and compo...

Enhancing biodiversity in cropping systems is suggested to promote ecosystem services, thereby reducing dependency on agronomic inputs while maintaining high crop yields. We assess the impact of several diversification practices in cropping systems on above- and belowground biodiversity and ecosystem services by reviewing 98 meta-analyses and perfo...

We used the Agricultural Production Systems sIMulator (APSIM) to predict and explain maize and soybean yields, phenology, and soil water and nitrogen (N) dynamics during the growing season in Iowa, USA. Historical, current and forecasted weather data were used to drive simulations, which were released in public four weeks after planting. In this pa...

Aims Root distributions determine crop nutrient access and soil carbon input patterns. To date, root distribution data are rare but needed to improve knowledge and prediction of cropping system sustainability. In this study, we sought to (i) quantify variation in maize (Zea mays) and soybean (Glycine max) roots by depth and environment across Iowa,...

Data S1. Materials and methods. Table S1. The 124 pre‐submitted research questions that address fundamental and applied issues in weed ecology, evolution and management

Diversification of grain-based cropping systems with forage legumes is commonly observed to enhance grain yields, yet the specific causes of this benefit remain poorly understood. One proposed cause is greater N availability, particularly late in the growing season, as these systems typically include organic N inputs such as legume residues and man...

Weedy plants pose a major threat to food security, biodiversity, ecosystem services and consequently to human health and wellbeing. However, many currently used weed management approaches are increasingly unsustainable. To address this knowledge and practice gap, in June 2014, 35 weed and invasion ecologists, weed scientists, evolutionary biologist...

Abstract Increasing nitrogen (N)-use efficiency (NUE) is key to improving crop production while mitigating ecologically-damaging environmental N losses. Traditional approaches to assess NUE are principally focused on evaluating crop responses to N inputs, often consider only what happens during the growing season, and ignore other means to improve...

Core Ideas EEM spectroscopy was used to characterize soluble OM pools in agricultural soils. PARAFAC was used to quantify OM meaningful EEM spectral components. PARAFAC components were correlated to N mineralization rates in specific sites. NPLS modeling of EEM data can estimate N mineralization rates in diverse soils. Rapid, easy, and frequent pr...

Quantitative measurements of root traits can improve our understanding of how crops respond to soil and weather conditions, but such data are rare. Our objective was to quantify maximum root depth and root front velocity (RFV) for maize (Zea mays) and soybean (Glycine max) crops across a range of growing conditions in the Midwest USA. Two sets of r...

Significance Prairie strips are a new conservation technology designed to alleviate biodiversity loss and environmental damage associated with row-crop agriculture. Results from a multiyear, catchment-scale experiment comparing corn and soybean fields with and without prairie vegetation indicated prairie strips raised pollinator and bird abundance,...

Core Ideas Gross N mineralization and PMN are related to different SOM properties. Multiple linear regressions generated predictions of N mineralization that were validated across diverse agroecosystems. Organic soil amendments consistently increased N mineralization. Gross N mineralization is a fundamental soil process that plays an important rol...

Plant root material makes a substantial contribution to the soil organic carbon (C) pool, but this contribution is disproportionate below 20 cm where 30 % of root mass and 50 % of soil organic C is found. Root carbon inputs changed drastically when native perennial plant systems were shifted to cultivated annual plant systems. We used the reconstru...

AimsHigh-yielding maize-based crop systems require maize to take up large quantities of nitrogen over short periods of time. Nitrogen management in conventional crop systems assumes that soil N mineralization alone cannot meet rapid rates of crop N uptake, and thus large pools of inorganic N, typically supplied as fertilizer, are required to meet c...

Non-chemical weed management covers all management practices that influence weeds except herbicides. This chapter summarises the major achievements in European research, as well as work undertaken in North America. Research groups from both continents have interacted strongly on the topic over the years and shared common interests on the developmen...

Plant root material makes a substantial contribution to the soil organic carbon (C) pool, but this contribution is disproportionate below 20 cm, where 30 % of root mass and 50 % of soil organic C is found. Root carbon inputs changed drastically when native perennial plant systems were shifted to cultivated annual plant systems. We used the reconstr...

Increasing crop rotation diversity while reducing herbicide applications may maintain effective weed control while reducing freshwater toxicity. To test this hypothesis, we applied the model USEtox 2.0 to data from a long-term Iowa field experiment that included three crop rotation systems: a 2-year corn-soybean sequence, a 3-year corn-soybean-oat/...

Plant-soil relations may explain why low-external input (LEI) diversified cropping systems are more efficient than their conventional counterparts. This work sought to identify links between management practices, soil quality changes, and root responses in a long-term cropping systems experiment in Iowa where grain yields of 3-year and 4-year LEI r...

Raw data for all soil and root parameters, Fall 2008-Spring 2010. (CSV)

Analysis of variance on means and stratification ratios on soils collected in spring, summer and fall of 2009. (XLSX)

Parameter estimates of linear regressions between summer root parameters and bulk density (Pr>F in parenthesis). (XLSX)

Raw data for carbon inputs to all crop phases. (CSV)

Soil parameter means for soils collected in spring, summer and fall of 2009 for all crop phases. (XLSX)

Transdisciplinary weed research (TWR) is a promising path to more effective management of challenging weed problems. We define TWR as an integrated process of inquiry and action that addresses complex weed problems in the context of broader efforts to improve economic, environmental and social aspects of ecosystem sustainability. TWR seeks to integ...

Weed management is a critically important activity on both agricultural and non-agricultural lands, but it is faced with a daunting set of challenges: environmental damage caused by control practices, weed resistance to herbicides, accelerated rates of weed dispersal through global trade, and greater weed impacts due to changes in climate and land...

Transdisciplinary weed research (TWR) is a promising path to more effective management of challenging weed problems. We define TWR as an integrated process of inquiry and action that addresses complex weed problems in the context of broader efforts to improve economic, environmental and social aspects of ecosystem sustainability. TWR seeks to integ...

We compare subsurface-drainage NO-N and total reactive phosphorus (TRP) concentrations and yields of select bioenergy cropping systems and their rotational phases. Cropping systems evaluated were grain-harvested corn-soybean rotations, grain- and stover-harvested continuous corn systems with and without a cover crop, and annually harvested reconstr...

Agricultural systems are being challenged to decrease water use and increase production while climate becomes more variable and the world's population grows. Low water use efficiency is traditionally characterized by high water use relative to low grain production and usually occurs under dry conditions. However, when a cropping system fails to tak...

Field experiments were conducted near Boone, IA, to quantify postdispersal seed predation of common lambsquarters and common waterhemp in corn (2003) and soybean (2004) managed with conventional, reduced, and zero-tillage systems. Seed predation in each tillage regime was quantified using selective exclusion treatments during July through September...

We studied temporal dynamics of above- and belowground growth and N use in three production systems: maize (C4 annual), reconstructed prairie (a mixture of perennial C3 and C4 species) and fertilized reconstructed prairie. Our objectives were to fill knowledge gaps about temporal patterns of growth (especially for roots), inform further experimenta...

Over the past two decades, ecologists have gained a considerable amount of insight concerning the effects of biological diversity on how ecosystems function. Greater productivity, greater carbon sequestration, greater retention of nutrients, and greater ability to resist and recover from various forms of stress, including herbivorous pests, disease...

Maize- and prairie-based systems were investigated as cellulosic feedstocks by conducting a 9 ha side-by-side comparison on fertile soils in the Midwestern United States. Maize was grown continuously with adequate fertilization over years both with and without a winter rye cover crop, and the 31-species reconstructed prairie was grown with and with...

Two broad aims drive weed science research: improved management and improved understanding of weed biology and ecology. In recent years, agricultural weed research addressing these two aims has effectively split into separate subdisciplines despite repeated calls for greater integration. Although some excellent work is being done, agricultural weed...

To improve our ability to predict SOC mineralization response to residue and N additions in soils with different inherent and dynamic organic matter properties, a 330-day incubation was conducted using samples from two long-term experiments (clay loam Mollisols in Iowa [IAsoil] and silt loam Ultisols in Maryland [MDsoil]) comparing conventional gra...

Weed seeds in and on the soil are the primary cause of weed infestations in arable fields. Previous studies have documented reductions in weed seedbanks due to cropping system diversification through extended rotation sequences, but the impacts of different rotation systems on additions to and losses from weed seedbanks remain poorly understood. We...

Cellulosic bioenergy production provides opportunities to utilize a range of cropping systems that can enhance the multifunctionality of agricultural landscapes. In a 9-ha field experiment located on fertile land in Boone County, IA, USA, we directly compared a corn-soybean rotation harvested for grain, continuous corn harvested for grain and stove...

Crop diversification has diminished in the USA during the past 50 years, and monocultures and short rotation sequences are currently the prevalent cropping systems. Simplification of cropping systems has been accompanied by greater reliance on synthetic pesticides and fertilizers to manage weeds, diseases and soil fertility, creating concerns about...

Overcoming the food, energy, environment “trilemma” poses a major societal challenge at present. Strategically integrating strips of native prairie within row-cropped agroecosystems has the potential to provide feasible answers to the trilemma. Twelve zero-order watersheds in Iowa have been monitored since 2007 to evaluate the range of ecosystem se...

Diversified cropping systems can have high soil microbial biomass and thus strong potential to reduce the weed seedbank through seed decay. This study, conducted in Iowa, USA, evaluated the hypothesis that weed seed decay is higher in a diversified 4-year maize–soyabean–oat/lucerne–lucerne cropping system than in a conventional 2-year maize–soyabea...

Cropping systems that include forage legumes and small grains in addition to corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] can achieve similar or higher crop productivity and economic return than simpler corn–soybean rotations. We hypothesized that this rotation effect occurs regardless of the crop genotype planted and the herbicide and c...

Background/Question/Methods With much of the U.S. Midwest in agricultural production and under private ownership, any viable conservation practice must fit within the context of currently profitable production systems. We study the ability of strategically integrated “prairie strips”—contour buffer and filter strips composed of diverse, native, p...

Background/Question/Methods Prairies are the native ecosystem in much of the central United States but have been largely replaced by annual crop production systems since Euro-American settlement. Cellulosic bioenergy production provides an opportunity to reincorporate prairies into agriculturally dominated landscapes, thereby enhancing the multif...

Overcoming the food-energy-environment “trilemma” poses a major societal challenge. Strategically integrating strips of native prairie vegetation within row-cropped agroecosystems does just this. A replicated watershed experiment in Iowa, USA, called STRIPs, establishes how prairie strips slow and purify water and provide habitat for native biodive...

Agriculture in the US Corn Belt is under increasing pressure to produce greater quantities of food, feed and fuel, while better protecting environmental quality. Key environmental problems in this region include water contamination by nutrients and herbicides emitted from cropland, a lack of non-agricultural habitat to support diverse communities o...

Over the past century, agricultural landscapes worldwide have increasingly been managed for the primary purpose of producing food, while other diverse ecosystem services potentially available from these landscapes have often been undervalued and diminished. The incorporation of relatively small amounts of perennial vegetation in strategic locations...

Using prairie biomass as a renewable source of energy may constitute an important opportunity to improve the environmental sustainability of managed land. To date, assessments of the feasibility of using prairies for bioenergy production have focused on marginal areas with low yield potential. Growing prairies on more fertile soil or with moderate...

Crop production and prevailing farming practices have greatly reduced biodiversity and nearly eliminated native prairie in the central USA. Restoring small areas of prairie on cropland may increase plant biodiversity and native species abundance while benefiting the cropland. In Iowa, we incorporated buffer strips composed of prairie vegetation wit...

Incorporating perennial, bioenergy crops like switchgrass (Panicum virgatum L.) into agricultural landscapes can provide harvestable biomass while improving ecosystem functions, but clear plant N management recommendations for switchgrass remain elusive. Delaying harvest until spring can reduce plant N concentration ([N]) but also harvestable yield...

Prairies used for bioenergy production have potential to generate marketable products while enhancing environmental quality, but little is known about how prairie species composition and nutrient management affect the suitability of prairie biomass for bioenergy production. We determined how functional‐group identity and nitrogen fertilization affe...

The Comparison of Biofuel Cropping Systems (COBS) project at Iowa State University is designed to provide a quantitative, side-by-side comparison of corn and multi-species perennial cropping systems. We are making comprehensive, long-term comparisons of contrasting biomass feedstock production systems with respect to: (a) potential for biomass prod...

Balancing productivity, profitability, and environmental health is a key challenge for agricultural sustainability. Most crop production systems in the United States are characterized by low species and management diversity, high use of fossil energy and agrichemicals, and large negative impacts on the environment. We hypothesized that cropping sys...

Mean monthly air temperature and total monthly precipitation during the 2003–2011 growing seasons, and long-term temperature and precipitation averages. Data were collected about 1 km from the experimental site in Boone Co., IA. (DOCX)

Aerial view of Marsden Farm study, Boone IA. Crop abbreviations: m = maize, sb = soybean, g = small grain, a = alfalfa. (TIF)

Crop identities and seeding rates in 2003–2011. (DOCX)

Herbicide applications in 2003–2011 to maize and soybean in the three rotation systems. No herbicides were used for triticale, oat, red clover, and alfalfa grown within the 3-yr and 4-yr systems. Reported application rates reflect the effect of banding of herbicides over crop rows in the 3-yr and 4-yr systems. (DOCX)

Detailed description of experimental site, management practices, scientific methods and statistical approach. (DOCX)

Macronutrients applied in manufactured fertilizers, herbicide adjuvants, and manure in 2003–2011. Manufactured N, P, and K fertilizers were applied at rates that varied among years and rotations in response to soil test results. Manure was applied at a rate of 15.7 Mg ha−1 in maize phases of the 3-year and 4-year rotation systems, but moisture and...

Simple and partial correlations between energy use within a given crop phase and mean rotation energy use and between energy use within a given crop phase and N fertilizer application rates. (DOCX)

Recent volatility in supplies and prices of natural gas and synthetic nitrogen (N) fertilizer suggests a need to develop and refine alternative strategies for supplying N to corn. In this study, conducted in north-eastern Iowa, we examined the use of red clover and alfalfa green manures as means of supplying N to a succeeding corn crop. Red clover...

Background/Question/Methods Agriculture in the U.S. Corn Belt is under increasing pressure to produce greater quantities of food and fuel while better protecting environmental quality. Key environmental problems in this region include water contamination by nutrients and herbicides emitted from cropland, a lack of non-agricultural habitat to suppo...

Sudden death syndrome (SDS) of soybean caused by Fusarium virguliforme is one of the most damaging diseases of soybean in the US. Management of SDS relies on selection of resistant varieties, cultural practices to improve soil drainage, and avoiding planting in cool, wet soils. The effectiveness of crop rotation for SDS management is not well under...

Conventional agriculture production systems in developed countries rely heavily on fossil energy, but emerging uncertainties in fossil fuel supply indicate a need to better understand energy efficiency in conventional and alternative systems. We used 6 yr of data from a cropping systems experiment conducted in Iowa to compare energy use of a conven...