Interactions between environmental conditions and management practices can significantly affect soil function. Soil quality assessments may improve our understanding of how soils interact with the hydrosphere and atmosphere. This information can then be used to develop management practices that improve the capacity of the soil to perform its various functions and help identify physical, chemical, and biological soil attributes to quantify the present state of a soil and detect changes resulting from management. In protocols established by the Great Plains cropping system network, sampling and testing procedures were selected to identify physical, chemical, and biological soil attributes responsive to management that may serve as useful indicators in assessing the effects of management on the soil resource. Eight existing long-term studies from throughout the Great Plains in the central USA were used to make these assessments because, (1) many years are required for certain soil properties to change measurably; (2) annual weather causes variation in system performance; and (3) the soil pools of interest are spatially variable. This paper includes detailed descriptions of the treatments and sites, and both long-term and short-term (1999–2002) data on precipitation, temperature, and yields for each location.

Agricultural systems produce both detrimental and beneficial effects on soil quality (SQ). We compared soil physical properties of long-term conventional (CON) and alternative (ALT) cropping systems near Akron, Colorado (CO); Brookings, South Dakota (SD); Bushland, Texas (TX); Fargo, North Dakota (ND); Mandan (ND); Mead, Nebraska (NE); Sidney, Montana (MT); and Swift Current, Saskatchewan (SK), Canada. Objectives were to quantify the changes in soil physical attributes in cropping systems and assess the potential of individual soil attributes as sensitive indicators of change in SQ. Soil samples were collected three times per year from each treatment at each site for one rotation cycle (4 years at Brookings and Mead). Water infiltration rates were measured. Soil bulk density (BD) and gravimetric water were measured at 0–7.5, 7.5–15, and 15–30 cm depth increments and water-filled pore space ratio (WFPS) was calculated. At six locations, a rotary sieve was used to separate soil (top 5 cm) into six aggregate size groups and calculate mean weight diameter (MWD) of dry aggregates. Under the CON system at Brookings, dry aggregates (>19 mm) abraded into the smallest size class (<0.4 mm) on sieving. In contrast, the large aggregates from the ALT system abraded into size classes between 2 and 6 mm. Dry aggregate size distribution (DASD) shows promise as an indicator of SQ related to susceptibility of soil to wind erosion. Aggregates from CON were least stable in water. Soil C was greater under ALT than CON for both Brookings and Mead. At other locations, MWD of aggregates under continuous crop or no tillage (ALT systems) was greater than MWD under CON. There was no crop system effect on water infiltration rates for locations having the same tillage within cropping system. Tillage resulted in increased, decreased, or unchanged near-surface BD. Because there was significant temporal variation in water infiltration, MWD, and BD, conclusions based on a single point-in-time observation should be avoided. Elevated WFPS at Fargo, Brookings, and Mead may have resulted in anaerobic soil conditions during a portion of the year. Repeated measurements of WFPS or DASD revealed important temporal characteristics of SQ that could be used to judge soil condition as affected by management.

Soil management and cropping systems have long-term effects on agronomic and environmental functions. This study examined the influence of contrasting management practices on selected soil chemical properties in eight long-term cropping system studies throughout the Great Plains and the western Corn Belt. For each study, soil organic C (SOC), total N (TN), particulate organic matter (POM), inorganic N, electrical conductivity (EC), and soil pH were evaluated at 0–7.5, 7.5–15, and 15–30 cm within conventional (CON) and alternative (ALT) cropping systems for 4 years (1999–2002). Treatment effects were primarily limited to the surface 7.5 cm of soil. No-tillage (NT) and/or elimination of fallow in ALT cropping systems resulted in significantly (P<0.05) greater SOC and TN at 0–7.5 cm within five of the eight study sites [Akron, Colorado (CO); Bushland, Texas (TX); Fargo, North Dakota (ND); Mandan, ND; and Swift Current, Saskatchewan (SK), Canada]. The same pattern was observed with POM, where POM was significantly (P<0.05) greater at four of the eight study sites [Bushland, TX, Mandan, ND, Sidney, Montana (MT), and Swift Current, SK]. No consistent pattern was observed with soil EC and pH due to management, although soil EC explained almost 60% of the variability in soil NO3-N at 0–7.5 cm across all locations and sampling times. In general, chemical soil properties measured in this study consistently exhibited values more conducive to crop production and environmental quality in ALT cropping systems relative to CON cropping systems.

Soil biological quality can affect key soil functions that support food production and environmental quality. The objective of this study was to determine the effects of management and time on soil biological quality in contrasting dryland cropping systems at eight locations in the North American Great Plains. Alternative (ALT) cropping systems were characterized by greater cropping intensity (less fallow), more diverse crop sequences, and/or reduced tillage than conventional (CON) cropping systems. Soil biological properties were assessed at depths of 0–7.5, 7.5–15, and 15–30 cm from 1999 to 2002 up to three times per year. Compared to CON, ALT cropping systems had greater microbial biomass and potentially mineralizable N. ALT cropping systems also had greater water stable aggregates in the surface 7.5 cm, but only at four locations. Total glomalin (TG), an organic fraction produced by fungi associated with aggregate stability, differed only at one location (Mandan), where the ALT cropping system had 27% more TG than the CON cropping system. Fatty acid methyl ester (FAME) profiles were highly location dependent, but total extracted FAME tended to be higher in ALT cropping systems. Soil biological properties fluctuated over time at all locations, possibly in response to weather, apparent changes in soil condition at sampling, and the presence or absence of fallow and/or legumes in rotation. Consequently, preplant and post-harvest sampling, when weather and soil conditions are most stable, is recommended for comparison of soil biological properties among management practices. Overall, ALT cropping systems enhanced soil function through: (1) improved retention and cycling of nutrients and (2) maintenance of biodiversity and habitat, implying improved agro-ecosystem performance over time.

Soils perform a number of essential functions affecting management goals. Soil functions were assessed by measuring physical, chemical, and biological properties in a regional assessment of conventional (CON) and alternative (ALT) management practices at eight sites within the Great Plains. The results, reported in accompanying papers, provide excellent data for assessing how management practices collectively affect agronomic and environmental soil functions that benefit both farmers and society. Our objective was to use the regional data as an input for two new assessment tools to evaluate their potential and sensitivity for detecting differences (aggradation or degradation) in management systems. The soil management assessment framework (SMAF) and the agro-ecosystem performance assessment tool (AEPAT) were used to score individual soil properties at each location relative to expected conditions based on inherent soil-forming factors and to compute index values that provide an overall assessment of the agronomic and environmental impact of the CON and ALT practices. SMAF index values were positively correlated with grain yield (an agronomic function) and total organic matter (an agronomic and environmental function). They were negatively correlated with soil nitrate concentration at harvest (an indicator of environmental function). There was general agreement between the two assessment tools when used to compare management practices. Users can measure a small number of soil properties and use one of these tools to easily assess the effectiveness of soil management practices. A higher score in either tool identifies more environmentally and agronomically sustainable management. Temporal variability in measured indicators makes dynamic assessments of management practices essential. Water-filled pore space, aggregate stability, particulate organic matter, and microbial biomass were sensitive to management and should be included in studies aimed at improving soil management. Reductions in both tillage and fallow combined with crop rotation has resulted in improved soil function (e.g., nutrient cycling, organic C content, and productivity) throughout the Great Plains.

A goal in sustainable agriculture is to use fossil fuel energy more efficiently in crop production. This 12-year study investigated effects of two crop rotations and two crop production systems (organic versus conventional management) on energy use, energy output and energy-use efficiency. The grain-based rotation included wheat (Triticum aestivum L.)–pea (Pisum sativum L.)–wheat–flax (Linum usitatissimum L.), while the integrated rotation included wheat–alfalfa (Medicago sativa L.)–alfalfa–flax. Energy use was 50% lower with organic than with conventional management, and approximately 40% lower with integrated than with the grain-based rotation. Energy use across all treatments averaged 3420 MJ ha−1 yr−1. Energy output (grain and alfalfa herbage only) across treatments averaged 49,947 MJ ha−1 yr−1 and was affected independently by production system and crop rotation. Energy output in the integrated rotation was three times that of the grain-based rotation; however, this difference was largely due to differences in crop type (whole plant alfalfa compared with grain seed). Energy output was 30% lower with organic than with conventional management. Energy efficiency (output energy/input energy) averaged to 17.4 and was highest in the organic and integrated rotations. A significant rotation by production system interaction (P<0.05) indicated that energy efficiency increases due to crop input reduction (i.e., shift from conventional to organic management) were greater in the integrated than in the grain-based rotation. Greater energy efficiency in the integrated rotation under organic management was attributed to the fact that the forage component was less sensitive to chemical input removal than grain crops.

Current production practices in the Red River Valley of North Dakota and Minnesota involve use of extensive tillage and/or herbicides to control weeds. Given the erosion potential, environmental concerns associated with herbicides, and herbicide-resistant weeds, alternative cropping systems that mitigate these problems need to be assessed economically. Furthermore, the role that government commodity programs play in the adoption of more ecologically friendly cropping systems needs to be determined. We evaluated 8 years of yield data (1994–2001) from field plots near Fargo, North Dakota, to compare the economics of two alternative cropping systems, reduced-input (RI) and no-till (NT), to a conventional tillage (CT) cropping system. The RI system relies on a more diverse rotation of soybean (SB), spring wheat (SW), sweet clover (SC) and rye, and uses fewer herbicide and fertilizer inputs than CT or NT. Both NT and CT systems rotate SB and SW. We found that CT returns averaged over $47 ha−1 more than NT during the study period. Because SC yield data were not available, the economic competitiveness of RI was calculated using break-even yields and returns for SC. Historical SC yields in Cass County, North Dakota were not statistically different from the break-even yields. However, when government program payments were considered, break-even returns for SC increased by about $15 and $18 ha−1 and break-even yields by 0.44 and 0.52 MT ha−1 for RI to compare with NT and CT, respectively. These results indicate that CT management offers greater economic return than either RI or NT and that government program payments impede adoption of more environmentally friendly cropping systems in the northern Great Plains.