Gary E. Varvel

Cropping system effects on soil quality in the Great Plains: Synthesis from a regional project

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.

Energy Potential and Greenhouse Gas Emissions from Bioenergy Cropping Systems on Marginally Productive Cropland

Low-carbon biofuel sources are being developed and evaluated in the United States and Europe to partially offset petroleum transport fuels. Current and potential biofuel production systems were evaluated from a long-term continuous no-tillage corn (Zea mays L.) and switchgrass (Panicum virgatum L.) field trial under differing harvest strategies and nitrogen (N) fertilizer intensities to determine overall environmental sustainability. Corn and switchgrass grown for bioenergy resulted in near-term net greenhouse gas (GHG) reductions of −29 to −396 grams of CO2 equivalent emissions per megajoule of ethanol per year as a result of direct soil carbon sequestration and from the adoption of integrated biofuel conversion pathways. Management practices in switchgrass and corn resulted in large variation in petroleum offset potential. Switchgrass, using best management practices produced 3919±117 liters of ethanol per hectare and had 74±2.2 gigajoules of petroleum offsets per hectare which was similar to intensified corn systems (grain and 50% residue harvest under optimal N rates). Co-locating and integrating cellulosic biorefineries with existing dry mill corn grain ethanol facilities improved net energy yields (GJ ha−1) of corn grain ethanol by >70%. A multi-feedstock, landscape approach coupled with an integrated biorefinery would be a viable option to meet growing renewable transportation fuel demands while improving the energy efficiency of first generation biofuels.

Cob biomass production in the western corn belt.

Corn residue is viewed as an abundant, inexpensive source of biomass that can be removed from fields for ethanol production without deleterious production or environmental effects if proper management is used according to some recent publications. Other publications indicate that corn residue needs to be retained on the land to reduce erosion and maintain or perhaps even improve soil organic matter levels. As researchers attempt to address these questions, one component of corn residue that may be available for immediate use for conversion to ethanol is the cob. Our objective was to determine how much cob biomass or cob biomass (as a percentage of grain biomass) is produced that could potentially be converted to biofuels. Results from two long-term experiments: 1) Rainfed with four cropping systems that included corn with three nitrogen fertilizer rates (20 years), and 2) Irrigated with two cropping systems, with four corn hybrids and five nitrogen fertilizer rates (8 years). Several factors (Cropping System, Hybrids, N fertilizer, and their interactions) significantly affected both cob biomass and cob biomass as a percent of grain biomass but were not of sufficient magnitude to be of practical significance. Most importantly, when N fertilizer was applied at rates sufficient to optimize grain yields in all cropping systems and hybrids, cob biomass as a percent of grain biomass averaged approximately 20%. This consistent relationship allows quick and easy calculation of the cob biomass that could be available for harvest for biofuels if grain yield levels or potentials are known.

Effects of Western Corn Belt Cropping Systems on Agroecosystem Functions

tices on agroecosystem functions is necessary to determine the sustainability of cropping systems. Agricultural sustainability is enhanced by management practices Performance-based indices have been used to assess that optimize the performance of multiple agroecosystem functions. the effects of management practices on agroecosystem The performance of western Corn Belt cropping systems was evalufunctions (Andrews et al., 2001; Glover et al., 2000; ated based on four agroecosystem functions: food production, raw materials production, nutrient cycling, and greenhouse gas regulation. Ericksen and McSweeney, 1999; Karlen and Stott, 1994). A simple multiattribute ranking procedure was used to quantify agroeThese indices use expert opinion or principal-compocosystem performance using data from a long-term cropping systems nent analysis to select indicators representative of speexperiment near Mead, NE. Treatments included in the procedure cific functions. Once selected, the indicators are scored were continuous corn (Zea mays L.) (CC), corn–soybean [Glycine based on their relative difference from a standard or max (L.) Merr.] (C–SB), corn–oat (Avena sativa L.) clover [80% optimum value using either linear or nonlinear techsweet clover (Melilotus officinalis L.) and 20% red clover (Trifolium niques. Scores within agroecosystem functions are typipratense L.)]–sorghum [Sorghum bicolor (L.) Moench]–soybean cally summed across functions, taking into consideration (C–OCL–SG–SB), and corn–soybean–sorghum–oat clover (C–SB– the relative importance of each function within the conSG–OCL) each at three N fertilization levels (ZERO, LOW, and text of climatic, geographical, and socioeconomic condiHIGH). Based on treatment averages of soil and crop indicators from 1983 to 1998, agroecosystem performance scores ranged from 66.6 to tions (Edwards and Newman, 1982; Stillwell et al., 1981). 77.3, with a least significant difference (LSD) between treatments of A simplified multiattribute ranking procedure using 2.2 (P 0.05). Treatments with the highest scores included C–OCL– a linear scoring technique was developed by Liebig et SG–SB/LOW (77.3), C–SB/LOW (76.9), CC/LOW (76.7), CC/HIGH al. (2001) to determine agroecosystem performance for (76.6), and C–SB–SG–OCL/LOW (75.3). Among these treatments, treatments in long-term experiments. The procedure those fertilized at the LOW N rate attained high scores through was successful in discriminating between conventional moderate performance in all four agroecosystem functions. The CC/ and alternative cropping systems when agroecosystem HIGH treatment, however, attained a high score solely through its performance was based on functions of food production, superior capacity to be highly productive, as its scores for the two raw materials production, nutrient cycling, and greenenvironmental quality–related functions were the lowest among all house gas regulation. Given the demonstrated utility of treatments. Correlations between productionand environmental prothe procedure to quantify the environmental dimension tection–related functions were negative, emphasizing the importance of agricultural sustainability, a more in-depth evaluation of employing management practices that are productive yet minimize deleterious environmental impacts. of its use is warranted. In this study, we sought to use the procedure to determine agroecosystem performance of four corn-based crop sequences (CC, C–SB, C–OCL– SG–SB, and C–SB–SG–OCL) each at three N fertilizaC systems perform multiple functions in tion levels for a long-term cropping systems experiment their role as agroecosystems. In addition to food, in the western Corn Belt. feed, and fiber production, cropping systems cycle nutrients, influence water partitioning within landscapes, and regulate greenhouse gas flux, thereby influencing enviMATERIALS AND METHODS ronmental quality as well as human and animal health Site Description (Costanza et al., 1997; Daily et al., 1997). The longData for this evaluation were used from a cropping systems term viability of cropping systems—or any agricultural experiment established in 1983 on the Agronomy Farm at the production system for that matter—is largely deterUniversity of Nebraska Agricultural Research and Developmined by how well these functions are executed within ment Center, approximately 6 km south of Mead, NE, in the context of the production, economic, and resource Saunders County (41 10 N, 96 25 W). The research site is conservation goals of agricultural producers. Conseon Peoria-age loess with nearly level topography (0–3% quently, quantifying the effects of management pracslope). The predominant soil is Sharpsburg silty clay loam (fine, smectitic, mesic Typic Argiudoll). The cropping systems study consisted of seven crop seM.A. Liebig, USDA-ARS, Northern Great Plains Res. Lab., P.O. quences (three monocultures, two 2-yr rotations, and two 4-yr Box 459, Mandan, ND 58554; and G.E. Varvel, USDA-ARS, Soil rotations) and three rates of N fertilizer (Varvel, 1994). Cornand Water Conserv. Res. Unit, 119 Keim Hall, Dep. of Agron., Univ. based cropping sequences included in the study were CC, of Nebraska, Lincoln, NE 68583-0934. The USDA-ARS is an equal opportunity/affirmative action employer, and all agency services are Abbreviations: CC, continuous corn, C–OCL–SG–SB, corn–oat available without discrimination. Received 10 Oct. 2001. *Correspondclover–sorghum–soybean; C–SB, corn–soybean; C–SB–SG–OCL, ing author (liebigm@mandan.ars.usda.gov). corn–soybean–sorghum–oat clover; HIGH, high N fertilization level; LOW, low N fertilization level; ZERO, zero N fertilization. Published in Agron. J. 95:316–322 (2003).

Great Plains cropping system studies for soil quality assessment

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.

Container and Installation Time Effects on Soil Moisture, Temperature, and Inorganic Nitrogen Retention for an in situ Nitrogen Mineralization Method

Mineralization contributes significantly to agronomic nitrogen (N) budgets and is difficult to accurately predict. Models for predicting N‐mineralization contributions are needed, and development of these models will require field‐based data. In situ mineralization methods are intended to quantify N mineralization under ambient environmental conditions. This study was conducted to compare soil moisture and temperature in intact soil cores contained in cylinders to those in adjacent bulk soil, compare the effect of two resin‐bag techniques on water content of soil within cylinders, and assess the effect of installation duration on inorganic N retention by resins. The study was conducted at a dryland conventionally tilled corn (Zea mays L.) site and an irrigated no‐tillage corn site in eastern Nebraska. Soil in cylinders was slightly wetter (<0.05 g g−1) and warmer (<1 °C) than adjacent soil. Soil water content was <80% water‐filled pore space (WFPS) at all sampling times and differed little between the two resin‐bag techniques. Greater soil water content and temperature conditions (though small) observed during most of the study period likely enhanced N mineralization within the cylinder compared to N mineralization in adjacent bulk soil, but the magnitude is likely much less than core‐to‐core variation normally observed in a field. Installing cylinders for more than 60 days resulted in loss of inorganic N from resins. Care is needed during installation to ensure that compaction of soil below the cylinder does not impede water movement through the intact soil core. The in situ method utilizing intact soil cores and resin bags replaced at 28‐ to 40‐day intervals is a viable method for measuring N mineralization.

Long-term no-till and stover retention each decrease the global warming potential of irrigated continuous corn

Over the last 50xa0years, the most increase in cultivated land area globally has been due to a doubling of irrigated land. Long-term agronomic management impacts on soil organic carbon (SOC) stocks, soil greenhouse gas (GHG) emissions, and global warming potential (GWP) in irrigated systems, however, remain relatively unknown. Here, residue and tillage management effects were quantified by measuring soil nitrous oxide (N2 O) and methane (CH4 ) fluxes and SOC changes (ΔSOC) at a long-term, irrigated continuous corn (Zea mays L.) system in eastern Nebraska, United States. Management treatments began in 2002, and measured treatments included no or high stover removal (0 or 6.8xa0Mgxa0DMxa0ha-1 xa0yr-1 , respectively) under no-till (NT) or conventional disk tillage (CT) with full irrigation (nxa0=xa04). Soil N2 O and CH4 fluxes were measured for five crop-years (2011-2015), and ΔSOC was determined on an equivalent mass basis to ~30xa0cm soil depth. Both area- and yield-scaled soil N2 O emissions were greater with stover retention compared to removal and for CT compared to NT, with no interaction between stover and tillage practices. Methane comprised <1% of total emissions, with NT being CH4 neutral and CT a CH4 source. Surface SOC decreased with stover removal and with CT after 14xa0years of management. When ΔSOC, soil GHG emissions, and agronomic energy usage were used to calculate system GWP, all management systems were net GHG sources. Conservation practices (NT, stover retention) each decreased system GWP compared to conventional practices (CT, stover removal), but pairing conservation practices conferred no additional mitigation benefit. Although cropping system, management equipment/timing/history, soil type, location, weather, and the depth to which ΔSOC is measured affect the GWP outcomes of irrigated systems at large, this long-term irrigated study provides valuable empirical evidence of how management decisions can impact soil GHG emissions and surface SOC stocks.

Big bluestem pasture in the Great Plains: an alternative for dryland corn.

Big bluestem pasture in the Great Plains: an alternative for dryland corn. DO:10.2458/azu_rangelands_v27i2_mitchell