Northern Great Plains Research Laboratory

Biochar has been heralded as an amendment to revitalize degraded soils, improve soil carbon sequestration, increase agronomic productivity, and enter into future carbon trading markets. However, scientific and economic technicalties may limit the ability of biochar to consistently deliver on these expectations. Past research has demonstrated that biochar is part of the black carbon continuum with variable properties due to the net result of production (e.g., feedstock and pyrolysis conditions) and postproduction factors (storage or activation). Therefore, biochar is not a single entity but rather spans a wide range of black carbon forms. Biochar is black carbon, but not all black carbon is biochar. Agronomic benefits arising from biochar additions to degraded soils have been emphasized, but negligible and negative agronomic effects have also been reported. Fifty percent of the reviewed studies reported yield increases after black carbon or biochar additions, with the remainder of the studies reporting alarming decreases to no significant differences. Hardwood biochar (black carbon) produced by traditional methods (kilns or soil pits) possessed the most consistent yield increases when added to soils. The universality of this conclusion requires further evaluation due to the highly skewed feedstock preferences within existing studies. With global population expanding while the amount of arable land remains limited, restoring soil quality to nonproductive soils could be key to meeting future global food production, food security, and energy supplies; biochar may play a role in this endeavor. Biochar economics are often marginally viable and are tightly tied to the assumed duration of agronomic benefits. Further research is needed to determine the conditions under which biochar can provide economic and agronomic benefits and to elucidate the fundamental mechanisms responsible for these benefits.

Diversifying cropping systems improves environmental health and has the potential to reduce risk from climate-change-related threats, but empirical evidence remains sparse. In this study, we found that maize yields were higher during adverse weather, including droughts, when maize was grown as part of a more diverse rotation. Rotation diversification also increased maize yields over time and under better growing conditions. Policies that support more diversified cropping systems could help reduce risk from increasingly stressful weather.

Abstract The positive effects of soil organic matter (OM) on soil properties that influence crop performance are well documented. But definitive and quantitative information of differential effects of soil OM contents is lacking for the northern Great Plains. The objective of this study was to quantify the contribution of a unit quantity of soil OM to productivity. Experiments were conducted on Williams loam (fine‐loamy, mixed, Typic Argiboroll) for 4 yr in the same field. The variables were soil OM content of the upper 30.5 cm together with all combinations of three postplanting soil available N levels (55, 90, and 125 kg N ha −1 as NO 3 ‐N to 1.2 m) and three water levels. Water levels were uniformly maintained with a trickle system that independently metered water to each plot for each soil available N level. Pretillering spring wheat ( Triticum aestivum L.) plant population decreased as soil OM content decreased in 3 of 4 yr. On an annual basis, highest total aerial dry matter and grain yields were associated with highest OM contents. The contribution of 1 Mg OM ha −1 to soil productivity, across the range of 64 to 142 Mg OM ha −1 , was calculated as equivalent to 35.2 kg ha −1 for spring wheat total aerial dry matter and 15.6 kg ha −1 for grain yield. Loss of productivity associated with a depletion of soil OM in the northern Great Plains is primarily a consequence of a concomitant loss of fertility.

Our objective is to provide an optimistic strategy for reversing soil degradation by increasing public and private research efforts to understand the role of soil biology, particularly microbiology, on the health of our world’s soils. We begin by defining soil quality/soil health (which we consider to be interchangeable terms), characterizing healthy soil resources, and relating the significance of soil health to agroecosystems and their functions. We examine how soil biology influences soil health and how biological properties and processes contribute to sustainability of agriculture and ecosystem services. We continue by examining what can be done to manipulate soil biology to: (i) increase nutrient availability for production of high yielding, high quality crops; (ii) protect crops from pests, pathogens, weeds; and (iii) manage other factors limiting production, provision of ecosystem services, and resilience to stresses like droughts. Next we look to the future by asking what needs to be known about soil biology that is not currently recognized or fully understood and how these needs could be addressed using emerging research tools. We conclude, based on our perceptions of how new knowledge regarding soil biology will help make agriculture more sustainable and productive, by recommending research emphases that should receive first priority through enhanced public and private research in order to reverse the trajectory toward global soil degradation.

Abstract Corn seeds ( Zea mays L. ‘WF9 × 38‐11’) were planted in plastic cylinders of soil at different bulk densities (0.93, 1.03, 1.13, and 1.23 g cm ‐3 ) or aggregates of different sizes (< 0.5, 0.5–1, 1–2, 2–3, and 3–6 mm). Soil water suction during germination was maintained at constant levels (0, 3, 18, 48, and 68 cm of water). Germination began and root elongation rates sharply increased from zero to a maximum in each soil sample as soil water suction increased above the air‐entry value or bubbling pressure. Over these ranges of suction, diffusion of O 2 controlled rate of root elongation. Diffusion of O 2 in soil was determined primarily by air porosity. Bulk density and aggregate size per se had little effect on diffusion or concentration of O 2 at seed depth. Bulk density and aggregate size greatly influenced soil water desorption, the depth of soil to which O 2 could diffuse, and the thickness of water films at equal air porosities. Between approximately 0 and 20 cm of suction, thickness of water films limited root elongation. Measured O 2 concentrations in soil agreed with concentrations predicted by diffusion theory. Redox potentials were correlated with O 2 levels. Root elongation rates decreased in some samples at the highest suctions used, probably because of increased soil strength.

Inclusion of cover crops (CCs) may be a potential strategy to boost no‐till performance by improving soil physical properties. To assess this potential, we utilized a winter wheat ( Triticum aestivum L.)–grain sorghum [ Sorghum bicolor (L.) Moench] rotation, four N rates, and a hairy vetch (HV; Vicia villosa Roth) CC after wheat during the first rotation cycles, which was replaced in subsequent cycles with sunn hemp (SH; Crotalaria juncea L.) and late‐maturing soybean [LMS; Glycine max (L.) Merr.] CCs in no‐till on a silt loam. At the end of 15 yr, we studied the cumulative impacts of CCs on soil physical properties and assessed relationships between soil properties and soil organic C (SOC) concentration. Across N rates, SH reduced near‐surface bulk density (ρ b ) by 4% and increased cumulative infiltration by three times relative to no‐CC plots. Without N application, SH and LMS reduced Proctor maximum ρ b , a parameter of soil compactibility, by 5%, indicating that soils under CCs may be less susceptible to compaction. Cover crops also increased mean weight diameter of aggregates (MWDA) by 80% in the 0‐ to 7.5‐cm depth. The SOC concentration was 30% greater for SH and 20% greater for LMS than for no‐CC plots in the 0‐ to 7.5‐cm depth. The CC‐induced increase in SOC concentration was negatively correlated with Proctor maximum ρ b and positively with MWDA and cumulative infiltration. Overall, addition of CCs to no‐till systems improved soil physical properties, and the CC‐induced change in SOC concentration was correlated with soil physical properties.

Diversification of cereal cropping systems with alternative crops, such as oilseed, pulse, and forage crops, furnishes producers with a range of agronomic and economic options. Crop diversification also improves management of plant diseases through manipulation of host factors such as crop and cultivar selection; interruption of disease cycles through crop rotation, fungicide application, and removal of weeds and volunteer crop plants; and modification of the microenvironment within the crop canopy using tillage practices and stand density. Management practices, such as seed treatment, date and rate of seeding, balanced fertility, control of weeds, field scouting, harvest management, and record keeping, can also be utilized to manage plant diseases. This review evaluates the risks to diversified crop production systems associated with the major plant diseases in the northern Great Plains and the influence of host, pathogen, and environmental factors on disease control. Principles to help producers reduce and manage the risk from plant diseases are presented, and discussion includes strategies for countering fusarium head blight ( Fusarium spp.), commonly called scab; and leaf spot diseases in cereals; sclerotinia stem rot [ Sclerotinia sclerotiorum (Lib.) De Bary] in oilseed and pulse crops; and ascochyta blight ( Ascochyta lentis Vassil.; teleomorph: Didymella lentis Kaiser, Wang & Rogers) and anthracnose blight [ Colletotrichum truncatum (Schwein.) Andrus & W.D. Moore] in pulse crops. Producers should not rely exclusively on a single management practice but rather integrate a combination of practices to develop a consistent long‐term strategy for disease management that is suited to their production system and location.

Abstract The size and turnover rate of the resistant soil organic matter (SOM) fractions were measured by 14 C dating and 13 C/ 12 C measurements. This involved soils archived in 1948, and recent samples, from a series of long‐term sites in the North American Great Plains. A reevaluation of C dates obtained in the 1960s expanded the study scope. The 14 C ages of surface soils were modern in some native sites and near modern in the low, moist areas of the landscape. They were much older at the catena summits. The 14 C ages were not related to latitude although this strongly influenced the total SOM content. Cultivation resulted in lower C contents and increased the 14 C age by an average of 900 yr. The 10‐ to 20‐cm depths from both cultivated and native sites were 1200 yr older than the 0‐ to 10‐cm depth. The 90‐ to 120‐cm depth of a cultivated site at 7015 yr before present (BP) was 6000 yr older than the surface. The nonhydrolyzable C of this depth dated 9035 yr BP. The residue of 6 M HCl hydrolysis comprised 23 to 70% of the total soil C and was, on the average, 1500 yr older. The percentage of nonhydrolyzable C and its 14 C age analytically identify the amount and turnover rate of the old resistant soil C.

The Soil Management Assessment Framework (SMAF) was developed to assess conservation effects on soil, and uses multiple soil quality indicator measurements to compare soil functioning. Our objective was to develop a SMAF‐compatible scoring equation for soil β‐glucosidase (BG) activity using published data sets representing different soils and management. The resulting equation was an S‐shaped curve: y = a /[1 + b exp(− cx )], where x is the measured BG activity (mg p ‐nitrophenol [PNP] released kg −1 soil h −1 ), a and b are constants, and c is a factor modified by soil classification, texture, and climate. Data from a study conducted near Mandan, ND were used to test the model for sensitivity to crop management systems. Soil organic C (SOC) content at the site measured 247 to 687 g kg −1 , while BG activity ranged from 33 to 675 mg kg −1 h −1 Using SMAF, SOC indicator scores ranged from 0.25 to 0.73, while BG activity scores varied from 0.17 to 0.93. As the work progressed, it became apparent that when BG activity values were normalized to the SOC content, the resulting ratio could indicate C sequestration trends, with ratios of 10 to 17 g PNP kg −1 SOC h −1 reflective of systems in equilibrium. Ratios >17 were mostly from recently altered management systems with SOC contents trending upward, while ratios <10 were generally from soils that were expected to continue to lose soil C. The application of a sensitive C cycling enzyme activity such as BG should improve the SMAF soil quality assessments for soil functions where soil metabolic activity or C‐cycle enzyme activity play a role.

Nitrous oxide (N 2 O) is often the largest single component of the greenhouse‐gas budget of individual cropping systems, as well as for the US agricultural sector as a whole. Here, we highlight the factors that make mitigating N 2 O emissions from fertilized agroecosystems such a difficult challenge, and discuss how these factors limit the effectiveness of existing practices and therefore require new technologies and fresh ideas. Modification of the rate, source, placement, and/or timing of nitrogen fertilizer application has in some cases been an effective way to reduce N 2 O emissions. However, the efficacy of existing approaches to reducing N 2 O emissions while maintaining crop yields across locations and growing seasons is uncertain because of the interaction of multiple factors that regulate several different N 2 O‐producing processes in soil. Although these processes have been well studied, our understanding of key aspects and our ability to manage them to mitigate N 2 O emissions remain limited.

Water is the driving variable in Great Plains agriculture and sustainability depends on efficient use of incident precipitation. Spring and winter wheat ( Triticum aestivum L.)‐fallow (SWF and WWF) farming systems, as currently practiced, are not economically sustainable without government subsidies. This paper synthesizes information regarding the water use efficiency (WUE) of intensified cropping systems in cultivated dryland agroecosystems and proposes solutions to ensure sustainablity. Decreasing tillage and maintaining crop residue on the soil is requisite to improved efficiency. No‐till fallow efficiency, the percentage of the precipitation stored during fallow, reached 40% in the early 1970s. However, scientists in the 1980s and 1990s still report fallow efficiencies no greater than 40%, indicating that other major system changes must occur if progress is to continue. Residue levels in the Great Plains usually are < 3 tons/acre and this probably has capped fallow efficiency near 40%. No‐till management of crop residues after spring or winter wheat harvest increases soil water storage in the first portion of the fallow (July to May) compared with conventional fallow management, but the soil in the late fallow period (June to September for winter wheat and June to May for spring wheat) gains no more water, and may even lose water relative to the quantity present in the spring. Overall system efficiency is best evaluated by calculating grain WUE values. Modern no‐till wheat‐fallow (WF) systems, even with maximum fallow efficiencies, only had average grain WUE of 104 lb/acre per in. for spring wheat and 140 lb/acre per in. for winter wheat. WUE for 3‐yr cropping systems, like winter wheat‐corn ( Zea mays L)‐fallow or winter wheat‐sorghum [ Sorghum bicolor (L.) Moench]‐fallow, increased WUE in Central and Southern Great Plains. Three year system WUE averaged 180 lb/acre per in., a 28% increase compared with WF. In the Northern Plains, continuous spring wheat systems averaged 122 lb/acre per in., a 15% increase compared with SWF. Individual crops within systems had the following potential WUE values: corn = 245 lb/acre per in., grain sorghum =225 lb/acre per in., proso millet ( Panicum miliuceum L). = 195 lb/acre per in., spring wheat = 216 lb/acre per in., and winter wheat = 150 lb/acre per in. Maximum system efficiency depends on choosing the most efficient plants for a given geographic area. Intensified cropping systems improve our ability to use precipitation efficiently. However, adoption of higher intensity cropping systems depends more on economic outcomes and government programs than on WUE or environmental effects. Research Question Water is the driving variable in Great Plains agriculture and sustainablity depends on efficient use of precipitation. If Great Plains agriculture is to be economically and environmentally sustainable, systems must be developed that maximize water storage efficiency and grain water use efficiency (WUE). The main objective of this paper was to synthesize existing information regarding the WUE of intensified cropping systems in the dryland environment of the Great Plains. Literature Summary For more than 80 years research scientists across the Great Plains have experimented with methods of improving water storage efficiency during summer fallow periods with the ultimate goal of increasing ensuing spring and winter wheat yields. It has been clearly demonstrated that reducing tillage and maintaining residue on the soil surface increases the percentage of the precipitation stored as soil water during fallow; this percentage is termed fallow eflciency . From 1916 until 1970, fallow efficiency increased from 19% to 35% as sweep tillage replaced plows and discs. By 1975, scientists had increased fallow efficiency to about 40% by using no‐till practices. Wheat yields increased proportionately as fallow efficiency increased. Recent efforts to increase fallow efficiency in wheat‐summer fallow systems beyond 40% have not been successful, and in fact wheat yields in no‐till fallow systems have not increased much beyond yields obtained with a reduced till system. The expense of storing the water during the summer fallow months with no‐till methods has not been recovered in added grain yield. Since 1980, there has been renewed effort to intensify cropping systems to improve overall WUE, a concept that was first explored in the 1960s. The most common of these attempts has been with 3‐yr systems like winter wheat‐corn‐fallow (WW‐C‐F) or winter wheat‐sorghum‐fallow (WW‐S‐F). Study Description We assembled published data from Montana, North and South Dakota, Nebraska, Kansas, Colorado, and Texas and synthesized the findings of experiments that compared intensified cropping systems with spring wheat‐fallow (SW‐F) and winter wheat‐fallow (WW‐F). The literature we reviewed usually reported a WUE for a particular crop in a particular system, but did not evaluate systems as a whole. Using the available data, we calculated a WUE for the entire system, which allowed us to directly compare the 2‐yr WW‐F with 3‐yr systems containing corn or sorghum or with continuous spring wheat. We also calculated WUE for 4‐yr systems and even continuous cropping when data were available. Applied Questions Have we learned how to increase fallow water storage efficiency in spring and winter wheat‐fallow systems by refining our no‐till technology? No‐till summer fallow efficiencies have not increased since the mid 1970s and it appears they are capped at about 40% because of the limited amount of residue we have available in our SW‐F and WW‐F systems. How efficient are the 3‐yr cropping systems compared with winter wheat‐fallow in the Central and Southern Great Plains? The 3‐yr systems, like WW‐C‐F and WW‐S‐F, produced 20 to 100 lb more grain per inch of water than did WW‐F (Fig. ). Intensified cropping systems produced an average of 55 lb more grain per inch of water than did WW‐F. How efficient is continuous spring wheat compared with spring wheat‐fallow in the Northern Great Plains? Continuous spring wheat grown in a no‐till system produced 18 lb more grain per inch of water than did SW‐F. This represents a 17% increase in WUE. How do crop plants differ in their individual water use efficiencies? Corn, sorghum, proso millet, and forage all produced more product per inch of water than did winter wheat (Fig. ). For example, corn and sorghum produced an average of 85 lb more grain per inch of water than did winter wheat. Spring wheat in the Northern Plains produced about the same amount of grain per inch of water as did corn in the Central Plains. Recommendation Producers currently using either SW‐F or WW‐F systems should consider adopting intensified systems. In the Central and Southern Plains, WW‐C‐F and WW‐S‐F are good alternatives to increase production efficiency. In the Northern Plains, continuous spring wheat or spring wheat‐sunflower rotations are good choices. Alternate crop‐fallow systems cannot take advantage of the excellent water storage that occurs in the first part of the summer fallow period using properly managed minimum and no‐till systems. By planting a spring crop, the producer can effectively use the stored water and avoid the expense of keeping fields weed‐free during the long summer fallow period associated with either SW‐F or WW‐F. Each producer must develop a particular cropping system to fit climatic and marketing situations. A general rule in developing the most profitable cropping system is to choose crops that have the highest potential WUE and that are adapted to a given climatic zone and local markets. Water use efficiency (WUE) comparison of winter wheat‐summer fallow (WW‐F) and intensified cropping systems at various Central and Southern Great Plains locations. WUE is pounds of grain produced per inch of water used during the growing season. image Water use efficiencies (WUE) for five agronomic crops. image

This study evaluates the dynamics of soil organic carbon (SOC) under perennial crops across the globe. It quantifies the effect of change from annual to perennial crops and the subsequent temporal changes in SOC stocks during the perennial crop cycle. It also presents an empirical model to estimate changes in the SOC content under crops as a function of time, land use, and site characteristics. We used a harmonized global dataset containing paired-comparison empirical values of SOC and different types of perennial crops (perennial grasses, palms, and woody plants) with different end uses: bioenergy, food, other bio-products, and short rotation coppice. Salient outcomes include: a 20-year period encompassing a change from annual to perennial crops led to an average 20% increase in SOC at 0-30 cm (6.0 ± 4.6 Mg/ha gain) and a total 10% increase over the 0-100 cm soil profile (5.7 ± 10.9 Mg/ha). A change from natural pasture to perennial crop decreased SOC stocks by 1% over 0-30 cm (-2.5 ± 4.2 Mg/ha) and 10% over 0-100 cm (-13.6 ± 8.9 Mg/ha). The effect of a land use change from forest to perennial crops did not show significant impacts, probably due to the limited number of plots; but the data indicated that while a 2% increase in SOC was observed at 0-30 cm (16.81 ± 55.1 Mg/ha), a decrease in 24% was observed at 30-100 cm (-40.1 ± 16.8 Mg/ha). Perennial crops generally accumulate SOC through time, especially woody crops; and temperature was the main driver explaining differences in SOC dynamics, followed by crop age, soil bulk density, clay content, and depth. We present empirical evidence showing that the FAO perennialization strategy is reasonable, underscoring the role of perennial crops as a useful component of climate change mitigation strategies.

Three mixed prairie sites at Mandan, N.D. were grazed heavily (0.9 ha steer-1), moderately (2.6 ha steer-1), or left ungrazed (exclosure) since 1916. These sites provided treatments to study the effects of long-term grazing on soil organic carbon and nitrogen content and to relate changes in soil carbon and nitrogen to grazing induced changes in species composition. Blue grama [Bouteloua gracilis (H.B.K) Lag. ex Griffiths] accounted for the greatest change in species composition for both grazing treatment. Relative foliar cover of blue grama was 25% in 1916 and 86% in 1994 in the heavily grazed pasture and 15% in 1916 to 16% in 1994 in the moderately grazed pasture. Total soil nitrogen content was higher in the exclosure (1.44 kg N ha-1) than in either grazing treatment (0.92 and 1.07 kg N ha-1 for moderately and heavily grazed, respectively) to 107-cm depth. Soil organic carbon content avg 72, 6.4, and 7A kg m-2 to 30.4 cm soil depth and 14.1,11.7, and 14.0 kg m-2 to 106.7 cm soil depth for the exclosure, moderately grazed, and heavily grazed treatments, respectively. Compared to the exclosure the moderately grazed pasture contained 17% less soil carbon to the 106.7 cm depth. Heavy grazing did not reduce soil carbon when compared to the exclosure. Based on 13C analysis and soil organic carbon data to 15.2 cm depth, blue grama or other C4 species contributed 24% or 12 kg m-2 of the total carbon in the heavily grazed and 20% or 0.8 kg m-2 of the total carbon in the moderately grazed pastures during the 1916 to l99l time period. The increase in blue grama, a species with dense shallow root systems, in the heavily grazed pasture probably accounted for maintenance of soil carbon at levels equal to the exclosure. These results suggest that changes in species composition from a mixed prairie to predominantly blue grama compensated for soil carbon losses that may result from grazing native grasslands.

Grasslands have an underground biomass component that serves as a carbon (C) storage sink. Switchgrass ( Panicum virgatum L.) has potential as a biofuel crop. Our objectives were to determine biomass and C partitioning in aboveground and belowground plant components and changes in soil organic C in switchgrass. Cultivars Sunburst and Dacotah were field grown over 3 yr at Mandan, ND. Aboveground biomass was sampled and separated into leaves, stems, senesced, and litter biomass. Root biomass to 1.1‐m depth and soil organic C to 0.9‐m depth was determined. Soil C loss from respiratory processes was determined by measuring CO 2 flux from early May to late October. At seed ripe harvest, stem biomass accounted for 46% of total aboveground biomass, leaves 7%, senesced plant parts 43%, and litter 4%. Excluding crowns, root biomass averaged 27% of the total plant biomass and 84% when crown tissue was included with root biomass. Carbon partitioning among aboveground, crown, and root biomass showed that crown tissue contained approximately 50% of the total biomass C. Regression analysis indicated that soil organic C to 0.9‐m depth increased at the rate of 1.01 kg C m −2 yr −1 Carbon lost through soil respiration processes was equal to 44% of the C content of the total plant biomass. Although an amount equal to nearly half of the C captured in plant biomass during a year is lost through soil respiration, these results suggest that northern Great Plains switchgrass plantings have potential for storing a significant quantity of soil C.

Recent precision‐agriculture research has focused on use of management zones (MZ) as a method for variable application of inputs like N. The objectives of this study were to determine (i) if landscape attributes could be aggregated into MZ that characterize spatial variation in soil chemical properties and corn yields and (ii) if temporal variability affects expression of yield spatial variability. This work was conducted on an irrigated cornfield near Gibbon, NE. Five landscape attributes, including a soil brightness image (red, green, and blue bands), elevation, and apparent electrical conductivity, were acquired for the field. A georeferenced soil‐sampling scheme was used to determine soil chemical properties (soil pH, electrical conductivity, P, and organic matter). Georeferenced yield monitor data were collected for five (1997–2001) seasons. The five landscape attributes were aggregated into four MZ using principal‐component analysis of landscape attributes and unsupervised classification of principal‐component scores. All of the soil chemical properties differed among the four MZ. While yields were observed to differ by up to 25% between the highest‐ and lowest‐yielding MZ in three of five seasons, receiving average precipitation, less‐pronounced (≤5%) differences were noted among the same MZ in the driest and wettest seasons. This illustrates the significant role temporal variability plays in altering yield spatial variability, even under irrigation. Use of MZ for variable application of inputs like N would only have been appropriate for this field in three out of the five seasons, seriously restricting the use of this approach under variable environmental conditions.

Successful dryland crop production in the semiarid Great Plains of North America must make efficient use of precipitation that is often limited and erratic in spatial and temporal distribution. The purpose of this paper is to review research on water use efficiency and precipitation use efficiency (PUE) as affected by cropping system and management in the Great Plains. Water use efficiency and PUE increase with residue management practices that increase precipitation storage efficiency, soil surface alterations that reduce runoff, cropping sequences that minimize fallow periods, and use of appropriate management practices for the selected crop. Precipitation use efficiency on a mass‐produced basis is highest for systems producing forage (14.5 kg ha −1 mm −1 ) and lowest for rotations with a high frequency of oilseed crops (4.2 kg ha −1 mm −1 ) or continuous small‐grain production in the southern plains (2.8 kg ha −1 mm −1 ). Precipitation use efficiency when calculated on a price‐received basis ranges from $1.20 ha −1 mm −1 (for an opportunity‐cropped system with 4 of 5 yr in forage production in the southern plains) to $0.30 ha −1 mm −1 {for a wheat ( Triticum aestivum L.)–grain sorghum [ Sorghum bicolor (L.) Moench]–fallow system in the southern plains}. Throughout the Great Plains region, PUE decreases with more southern latitudes for rotations of similar makeup of cereals, pulses, oilseeds, and forages. Forage systems in the southern Great Plains appear to be highly efficient when PUE is computed on a price‐received basis. In general across the Great Plains, increasing intensity of cropping increases PUE on both a mass‐produced basis and on a price‐received basis.

Water is the principle limiting factor in dryland cropping systems. Surface soil physical properties influence infiltration and cropping systems under no‐till management may affect these properties through residue addition. The objectives of this study were: (i) to determine how cropping intensity and topographic position affect soil bulk density, porosity, sorptivity, and aggregate stability in the surface 2.5 cm of soils at three eastern Colorado sites; and (ii) to relate these properties to crop residue returned to the soil surface. No‐till cropping systems had been in place on three slope positions, at three sites, for 12 yr prior to this study. Wheat ( Triticum aestivum L.)‐corn ( Zea mays L.)‐fallow (WCF) and continuous cropping (CC) systems were compared with wheat‐fallow (WF) on summit and toeslope positions at two sites (Sterling and Stratton), and at the third site (Walsh) wheat‐sorghum [ Sorghum bicolor (L.) Moench]‐fallow (WSF) replaced WCF. Cropping systems (CC and WCF or WSF) that returned more crop residue decreased bulk density and increased total and effective porosities compared with WF. Site and slope positions that produced more crop residue also improved these properties. However, sorptivity developed no significant differences as a result of cropping system. Macroaggregates made up a higher percentage of total aggregates in CC and WCF or WSF compared with WF in proportion to residue added and were also a function of clay content of the soil at different sites and slope positions. These factors enhance the potential for greater infiltration and hence greater water availability for crops.

Anecdotal accounts regarding reduced US cropping system diversity have raised concerns about negative impacts of increasingly homogeneous cropping systems. However, formal analyses to document such changes are lacking. Using US Agriculture Census data, which are collected every five years, we quantified crop species diversity from 1978 to 2012, for the contiguous US on a county level basis. We used Shannon diversity indices expressed as effective number of crop species (ENCS) to quantify crop diversity. We then evaluated changes in county-level crop diversity both nationally and for each of the eight Farm Resource Regions developed by the National Agriculture Statistics Service. During the 34 years we considered in our analyses, both national and regional ENCS changed. Nationally, crop diversity was lower in 2012 than in 1978. However, our analyses also revealed interesting trends between and within different Resource Regions. Overall, the Heartland Resource Region had the lowest crop diversity whereas the Fruitful Rim and Northern Crescent had the highest. In contrast to the other Resource Regions, the Mississippi Portal had significantly higher crop diversity in 2012 than in 1978. Also, within regions there were differences between counties in crop diversity. Spatial autocorrelation revealed clustering of low and high ENCS and this trend became stronger over time. These results show that, nationally counties have been clustering into areas of either low diversity or high diversity. Moreover, a significant trend of more counties shifting to lower rather than to higher crop diversity was detected. The clustering and shifting demonstrates a trend toward crop diversity loss and attendant homogenization of agricultural production systems, which could have far-reaching consequences for provision of ecosystem system services associated with agricultural systems as well as food system sustainability.

Five long‐term tillage studies in Kansas were evaluated for changes in soil properties including soil organic carbon (SOC), water holding capacity (WHC), bulk density, and aggregate stability. The average length of time these studies have been conducted was 23 yr. Soil properties were characterized in three depth increments to 30 cm, yet changes due to tillage, N fertility, or crop rotation were found primarily in the upper 0‐ to 5‐cm depth. Decreased tillage intensity, increased N fertilization, and crop rotations that included cereal crops had greater SOC in the 0‐ to 5‐cm soil depth. Only one of five sites had greater WHC, which occurred in the 0‐ to 5‐cm depth. Aggregate stability was highly correlated with SOC at all sites. No‐tillage (NT) had greater bulk density, but values remained below that considered root limiting. Soil organic C levels can be modified by management that can improve aggregate stability, but greater SOC did not result in greater WHC for the majority of soils evaluated in this study.

Evaluating the impact agricultural practices have on agroecosystem functions is essential to determine the sustainability of management systems. This paper presents an approach to determine the relative sustainability of agricultural practices. A simple ranking procedure using a relative scoring method is proposed to discriminate among treatments based on the status of crop and soil parameters within different agroecosystem functions. Summing scores across agroecosystem functions allows for the identification of agricultural practices that are performing optimally based on functions included in the procedure. An example, using data from a long‐term cropping systems experiment in the western Corn Belt, found the indexing procedure to successfully discern differences in overall performance across four agroecosystem functions between conventional [continuous corn ( Zea mays L.) cropping sequence at a fertilization rate of 180 kg N ha −1 ] and alternative {corn–oat ( Avena sativa L.) + clover ( Trifolium pratense L.)–grain sorghum [ Sorghum bicolor (L.) Moench]–soybean [ Glycine max (L.) Merr.] cropping sequence at a fertilization rate of 90 kg N ha −1 } management systems. The simplicity, inclusiveness, and inherent flexibility of the indexing procedure can be considered benefits and drawbacks, depending on the point of view taken. Data requirements of the approach, however, are stringent. Consequently, its most appropriate use may be with data from long‐term agroecosystem experiments.