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Traditional sampling methods are inadequate for assessing the interrelated physical, chemical, and biological soil properties responsible for variations in agronomic yield and ecological potentials across a landscape. Recent advances in computers, global positioning systems, and large‐scale sensors offer new opportunities for mapping heterogeneous patterns in soil condition. We evaluated field‐scale apparent electrical conductivity (ECa) mapping for delineating soil properties correlated with productivity and ecological properties. A contiguous section of farmland (250 ha), managed as eight fields in a no‐till winter wheat (Triticum aestivum L.)–corn (Zea mays L.)–millet (Panicum miliaceum L.)–fallow rotation, was ECa mapped (≈0‐ to 30‐cm depth). A geo‐referenced soil‐sampling scheme separated each field into four ECa classes that were sampled (0‐ to 7.5‐ and 7.5‐ to 30‐cm depths) in triplicate. Soil physical parameters (bulk density, moisture content, and percentage clay), chemical parameters (total and particulate organic matter [POM], total C and N, extractable P, laboratory‐measured electrical conductivity [EC1:1], and pH), biological parameters (microbial biomass C [MBC] and N [MBN], and potentially mineralizable N), and surface residue mass were significantly different among ECa classes (P ≤ 0.06) at one or both depths (0–7.5 and 0–30 cm). Bulk density, percentage clay, EC1:1, and pH were positively correlated with ECa; all other soil parameters and surface residue mass were negatively correlated. Field‐scale ECa classification delimits distinct zones of soil condition, providing an effective basis for soil sampling. Potential uses include assessing temporal impacts of management on soil condition and managing spatial variation in soil‐condition and yield‐potential through precision agriculture and site‐specific management.

With increased cropping intensity, one would expect that more crop residue and C would be added to the Soil C sequestration can improve soil quality and reduce agriculsoil than with a crop-fallow system (Campbell et al., ture's contribution to CO 2 emissions. The long-term (12 yr) effects of tillage system and N fertilization on crop residue production and 1995, 2000b; Janzen et al., 1998a; Peterson et al., 1998). soil organic C (SOC) sequestration in two dryland cropping systems As the amount of crop residue returned to the soil is in North Dakota on a loam soil were evaluated. An annual cropping increased, SOC sequestration is expected to increase if (AC) rotation [spring wheat (SW) (Triticum aestivum L.)-winter the residue C is not lost as CO 2 to the atmosphere wheat (WW)-sunflower (SF) (Helianthus annuus L.)] and a spring because of tillage induced decomposition (Larney et al., wheat-fallow (SW-F) rotation were studied. Tillage systems included 1997; Reicosky, 1997a,b). Research in the Great Plains conventional-till (CT), minimum-till (MT), and no-till (NT). Nitrogen has shown that SOC sequestration is enhanced by N rates were 34, 67, and 101 kg N ha Ϫ1 for the AC system and 0, 22, fertilization (Campbell and Zentner, 1993; Campbell et and 45 kg N ha Ϫ1 for the SW-F system. Total crop residue returned

The extreme climate of the northern Great Plains of North America requires cropping systems to possess a resilient soil resource in order to be sustainable. This paper summarizes the interactive effects of tillage, crop sequence, and cropping intensity on soil quality indicators for two long-term cropping system experiments in the northern Great Plains. The experiments, located in central North Dakota, were established in 1984 and 1993 on a Wilton silt loam (FAO: Calcic Siltic Chernozem; USDA 1 : fine-silty, mixed, superactive frigid Pachic Haplustoll). Soil physical, chemical, and biological properties considered as indicators of soil quality were evaluated in spring 2001 in both experiments at depths of 0-7.5, 7.5-15, and 15-30 cm. Management effects on soil properties were largely limited to the surface 7.5 cm in both experiments. For the experiment established in 1984, differences in soil condition between a continuous crop, no-till system and a crop-fallow, conventional tillage system were substantial. Within the surface 7.5 cm, the continuous crop, no-till system possessed significantly more soil organic C (by 7.28 Mg ha −1 ), particulate organic matter C (POM-C) (by 4.98 Mg ha −1 ), potentially mineralizable N (PMN) (by 32.4 kg ha −1 ), and microbial biomass C (by 586 kg ha −1 ), as well as greater aggregate stability (by 33.4%) and faster infiltration rates (by 55.6 cm h −1 ) relative to the crop-fallow, conventional tillage system. Thus, soil from the continuous crop, no-till system was improved with respect to its ability to provide a source for plant nutrients, withstand erosion, and facilitate water transfer. Soil properties were affected less by management practices in the experiment established in 1993, although organic matter related properties tended to be greater under continuous cropping or minimum tillage than crop sequences with fallow or no-till. In particular, PMN and microbial biomass C were greatest in continuous spring wheat (with residue removed) (22.5 kg ha −1 for PMN; 792 kg ha −1 for microbial biomass C) as compared with sequences with fallow (SW-S-F and SW-F) (Average = 15.9 kg ha −1 for PMN; 577 kg ha −1 for microbial biomass C). Results from both experiments confirm that farmers in the northern Great Plains of North America can improve soil quality and agricultural sustainability by adopting production systems that employ intensive cropping practices with reduced tillage management.

There is concern that antibiotic resistance can potentially be transferred from animals to humans through the food chain. The relationship between specific antibiotic resistant bacteria and the genes they carry remains to be described. Few details are known about the ecology of antibiotic resistant genes and bacteria in food production systems, or how antibiotic resistance genes in food animals compare to antibiotic resistance genes in other ecosystems. Here we report the distribution of antibiotic resistant genes in publicly available agricultural and non-agricultural metagenomic samples and identify which bacteria are likely to be carrying those genes. Antibiotic resistance, as coded for in the genes used in this study, is a process that was associated with all natural, agricultural, and human-impacted ecosystems examined, with between 0.7 to 4.4% of all classified genes in each habitat coding for resistance to antibiotic and toxic compounds (RATC). Agricultural, human, and coastal-marine metagenomes have characteristic distributions of antibiotic resistance genes, and different bacteria that carry the genes. There is a larger percentage of the total genome associated with antibiotic resistance in gastrointestinal-associated and agricultural metagenomes compared to marine and Antarctic samples. Since antibiotic resistance genes are a natural part of both human-impacted and pristine habitats, presence of these resistance genes in any specific habitat is therefore not sufficient to indicate or determine impact of anthropogenic antibiotic use. We recommend that baseline studies and control samples be taken in order to determine natural background levels of antibiotic resistant bacteria and/or antibiotic resistance genes when investigating the impacts of veterinary use of antibiotics on human health. We raise questions regarding whether the underlying biology of each type of bacteria contributes to the likelihood of transfer via the food chain.

corn-soybean cropping systems predominate. The effect of these cropping systems on indicators of soil quality Understanding long-term management effects on soil properties is only partially understood. Soil organic C has been is necessary to determine the relative sustainability of cropping systems. Soil physical, chemical, and biological properties were measured shown to increase in monoculture corn where N fertilin a long-term cropping system study in the Western Corn Belt. Prop-ization is adequate and no-till is used (Studdert and erties were evaluated after 16 yr in four crop sequences [continuous

An increasing human population is placing greater demand on soil resources, and as a result degradation is taking place in many regions of the world. This is critical because soils perform a number of essential processes including supporting food and fiber production, influencing air quality through interaction with the atmosphere, and serving as a medium for storage and purification of water. The soil quality concept was introduced to complement soil science research by making our understanding of soils more complete and helping guide the use and allocation of labor, energy, fiscal, and other inputs as agriculture intensifies and expands to meet increasing world demands. Soil quality thus provides a unifying concept for educating professionals, producers, and the public about the important processes that soils perform. It also provides an assessment tool for evaluating current management practices and comparing alternative management practices. Soil attributes comprising a minimum data set have been identified, and both laboratory and field methods have been developed for measuring them. A soil quality index is being developed to normalize measured soil quality indicator data and generate a numeric value that can be used to compare various management practices or to assess management-induced changes over time. Using previously published data, we evaluated the soil quality index as a tool to assess a wide range of management practices in the Northern Great Plains. The index ranked the treatments: grazed fertilized tame pasture > moderately grazed > ungrazed > heavily grazed > annual cropping with no-tillage > conventionally tilled crop-fallow which agrees with the way they were subjectively ranked in the publications. The soil quality index shows potential for use as a management assessment tool.