In 1998, researchers at Iowa State University (ISU) participated in a second year of precision-agriculture-related studies at Sorenson Farm. Located a few miles west of Ames, the farm is a 75-acre field laboratory dedicated to the study of site-specific crop management practices.

The decision to establish a dedicated site arose from recognition of the need to test precision agriculture technologies on a larger scale than would be possible with small-plot research. Also, implementing experiments at a dedicated site--rather than scattering studies among several research farms--provides information from multiple years and a variety of projects. Researchers from crop production, soil fertility, weed science, plant pathology, soil science, and agricultural engineering are participating in studies at the farm. ISU's Sorenson Farm constitutes a valuable, long-term study of precision agriculture technologies implemented on a real-world scale.

Since 1996, aerial images have been used to document site conditions, identify variation in crop response, and record locations of specific problems. Site characteristics were studied in detail and mapped in 1997. Intensive grid sampling indicated that soils vary considerably in nutrient levels, pH, and drainage properties. In 1998, strip plots were established for specific experiments and treatments were applied. Current projects focus on assessment of yield responses and economic benefits obtained from implementing new management practices.

Roughly half of the farm is being used to examine questions related to new fertilizer application methods. Areas with variation in pH and soil phosphorus levels were identified. Both fixed-rate and variable-rate applications of lime and phosphorus were applied in replicated strips. Researchers conducted intensive sampling programs to monitor soil nutrient levels and plant uptake. After a second year of data collection, crop responses and economic benefits for the two application methods will be compared.

Another focus of fertility management is the potential for minimizing nitrogen (N) losses by applying N as a side-dress application in late spring. In 1997 and 1998, several N application rates were tested to identify minimum rates for adequate fertilization. Researchers also are investigating whether or not delayed N applications provide adequate fertility. Results from the study, which will continue in 1999, will be used to develop recommendations for late-spring N application.

Plant pathologists are using the site to examine relationships between disease incidence, site factors, and yield losses. Areas with both severe soybean cyst nematode (SCN) infestations and variable soil properties present an ideal opportunity to evaluate the performance of SCN-resistant soybean varieties for SCN management and yield performance. Strip trials comparing SCN-resistant and SCN-susceptible varieties were implemented last year and will continue in 1999.

Weed scientists completed a profile of species in the weed seed bank. The farm contains weed patches that have been present for several years, and the association between site factors and weed species is of interest. Because of the wet spring, weed management options were limited and weed populations flourished, particularly in flooded areas. Consequently, contributions to the seed bank following the 1998 cropping season will be of particular interest.

A major factor influencing crop yields and experimental results was heavy rainfall early in the 1998 growing season. Crops failed to recover in areas that experienced long-term flooding in late spring. Approximately 10.1 acres was flooded for several weeks, and complete crop loss occurred on 6.3 acres. Yield maps from previous years indicate that variation in soil drainage properties influences yields at the farm, even in drier years. Last year, researchers installed a permanent weather station and 10-foot-deep wells for use in monitoring fluctuations in rainfall amounts and water-table depth. Continued assessment of soil characteristics, via electromagnetic induction profiles and aerial images, is being used by soil scientists to evaluate the influence of soil structure and drainage characteristics on yield variation.

Geographic information system (GIS) analysis is a key tool for compiling data from various sampling approaches and from multiple years. The ability to consider site factors, crop responses, and yield variations in time when evaluating management practices requires appropriate computer capacity and programs. For that purpose a GIS laboratory has been established in the ISU Agronomy Department for use by all researchers working on precision agriculture projects. It is hoped that understanding obtained from activities at Sorenson Farm and the new GIS laboratory will result in practical information for crop producers who are using precision agriculture technologies.