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.

A soil sampler, elutriator, and associated sample flushing device were designed and constructed for an intensive study of weed seedbanks. This equipment was used in 1993 to collect and process 4980 soil samples. The sampler was durable, core size was consistent, and sampling was efficient. Cores were approximately 200 cm3and two people could take 120 cores/h. The elutriator separated weed seeds from 36 of these cores at a time. Washing required 60 to 75 min depending on soil texture. Seeds as small as 0.3 mm in diam were recovered and almost 100% of the seeds were recovered from samples spiked with barnyardgrass, redroot pigweed, velvetleaf, and witchgrass. The flushing device was used to transfer sample contents from strainers of the elutriator to propyltex bags for drying and storing. Equipment like this, plus improved technology for identifying and counting seeds, is needed to make weed seedbank studies more feasible.

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Furrow irrigation is commonly used to provide supplemental water to row crops. Alternate‐furrow irrigation has been proposed as a method to decrease deep percolation water losses as well as the leaching of fertilizer and pesticides. A study was conducted on a Ulm clay loam (fine, smectitic, mesic Ustic Haplargids) in 1994 and 1995 near Fort Collins, CO. Corn (Zea mays L.) growth and N uptake were measured under alternate‐furrow and every‐furrow irrigation water applications, each with fertilizer bands placed either in the row or in the furrow. Nitrogen‐15‐depleted (NH4)2SO4 fertilizer was used to distinguish plant uptake of fertilizer N from uptake of naturally occurring N. There were no differences in plant response to alternate‐furrow or every‐furrow irrigation water placement for the same amount of water applied. Greater fertilizer‐N uptake occurred with row placement than with furrow placement of N fertilizer. Early in the growing season, fertilizer‐N uptake from row placement was from 2 to 10 times the fertilizer‐N uptake from furrow placement. By the end of the growing season, the average total‐N uptake from row placement was 12% greater than for furrow placement. Placing the fertilizer in the nonirrigated furrow of the alternate‐furrow irrigation treatment decreased N availability by 20% compared with the average of the other treatments. If alternate‐furrow irrigation is used to increase water use efficiency in furrow‐irrigated fields, placing the N fertilizer in the nonirrigated furrow of the alternate‐furrow irrigation system could decrease N availability because of drier soil conditions in the nonirrigated furrow. Row placement of N fertilizer seems to be beneficial in both alternate‐furrow and every‐furrow irrigation applications.

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A vacuum extractor, consisting of a porous ceramic tube within a sheet‐metal trough, has been developed to provide a quantitative measure of soil water lost by deep percolation and to provide a water sample for chemical analysis. Several of these extractors have been installed in the field and preliminary field performance is reported. Detailed laboratory evaluation is in progress.

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