A practical variable‐rate fertilizer application should be based on information gathered at low cost that represents field fertility levels. The number of soil samples gathered and analyzed may limit the effectiveness of some variable‐rate fertilizer applications. Topography‐based soil sampling is attractive because it suggests a lower number of samples needed to characterize fertility levels and patterns in a field than some current grid sampling recommendations. A 40‐acre North Dakota field consisting of Barnes loam (fine loamy, mixed, Udic Haploborolls), Swenoda loam (mixed, Pachic Udic Haploborolls), and Wyard clay loam (fine loamy, mixed, frigid Typic Haplaquolls) soil types was sampled in a 110 ft grid each fall from 1994 to 1996. Nitrate N, P, sulfate S, and chloride level patterns were similar in all 3 yr. Correlation of both area‐ (sample cores obtained from a wide area within a topography zone) and point‐based (a topography zone represented by a composite taken from a point location) topography sampling with the 110 ft grid values was compared with correlation from a 220 ft, 330 ft, and 5 acre grid. Area‐based topography sampling for nitrate N was superior in correlation to the 220 ft grid values in 2 of 3 yr. Area‐based topography sampling with P was superior to the 220 ft grid in only 1 of 3 yr, but was superior to the 5 acre grid in all years. The 220 ft grid was superior to topography sampling for sulfate S in all years, but area‐based topography sampling was better than the 330 ft grid in 2 of 3 yr and superior to the 5 acre grid in all years. Area‐based topography sampling for chloride was superior to the 220 ft grid in 1 of 3 yr, but was more highly correlated with the 110 ft grid than the 330 ft and 5 acre grid in all years. Area‐based topography sampling was more highly correlated than point‐based topography sampling in seven of 12 comparisons. Topography‐based sampling for nitrate N better represented fertility patterns than did grid sampling. Research Question In order for variable‐rate fertilizer application to be practical, soil testing information must be gathered at low cost, but at the same time represent the variation in field soil fertility levels. Since collecting and analyzing soil samples is expensive, minimizing the number of samples collected while maintaining a high level of soil fertility information is important. This study of one North Dakota field compared the use of topography‐based sampling with selected grid methods for nitrate N, P, sulfate S, and chloride to determine whether topography‐based sampling might compare favorably with information gathered from grid sampling methods, while decreasing the number of samples needed to provide similar or superior soil fertility information. Literature Summary Previous work in Wisconsin and Illinois has suggested that a one sample per acre grid might be required to gather soil fertility information needed for a variable‐rate fertilizer application. Other studies have demonstrated that some soil fertility factors may be related to l...

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A field trial was conducted at Fargo, North Dakota, in 2005 and 2006 to evaluate different fungicide application methods on soybean (Glycine max). Kromekote ® paper cards were placed in the upper and lower canopy of soybean plants, and tebuconazole fungicide mixed with a blue dye was sprayed with different application methods at the R5 developmental stage. The applications were made with a conventional sprayer with Turbo TeeJet ® 110015 flatfan nozzles at 276 kPa liquid pressure, a conventional sprayer with XR TeeJet ® 80015 flat-fan nozzles at 276 kPa liquid pressure, an AirJet ® bifluid nozzle spray system with liquid pressure at 276 kPa and air pressure at both 76 and 48 kPa, or an air-assisted spray system with liquid pressure at both 221 and 83 kPa. An untreated control was also included to evaluate the effect of tebuconazole on soybean yield. Dye-sensitive Kromekote paper cards were analyzed to determine the percent coverage and the volume median diameter (VMD) of the droplets. Significant (P ≤ 0.05) interactions between year and application method were detected, most likely resulting from differences in plant height and development between the years. Droplet coverage in the upper canopy did not differ in either year among the application methods. Most application methods provided similar droplet coverage in the lower canopy in 2005, but the conventional sprayer with XR TeeJet 80015 flat-fan nozzles provided the greatest coverage in the lower canopy in 2006. Correlation analysis indicated that droplet coverage in the lower canopy increased with increased VMD of the droplets in 2005 (R = 0.91), and that yield increased with increased fungicide coverage in 2006 (R = 0.85). Visible symptoms of foliar fungal diseases were not present in either year, and tebuconazole had no effect on soybean yield, compared with the untreated control in either year. Bradley et al.: soybean / fungicide application / comparison of methods 202 Résumé : En 2005 et 2006, un essai au champ fut mené à Fargo, Dakota du Nord, pour évaluer différentes méthodes d'application de fongicides sur le soja (Glycine max). Des cartes de papier Kromekotez furent placées aux niveaux supérieur et inférieur du couvert végétal du soja, et du fongicide tébuconazole, mélangé à un colorant bleu, fut pulvérisé selon différentes méthodes d'application au stade de développement R5. Les applications ont été effectuées avec un pulvérisateur traditionnel équipé de buses à jet plat Turbo TeeJetz 110015 à une pression du liquide de 276 kPa, un pulvérisateur traditionnel équipé de buses à jet plat XR TeeJetz 80015 à une pression du liquide de 276 kPa, un système de pulvérisation équipé de buses AirJetz à émulsions inverties multiphases à une pression du liquide de 276 kPa et une pression d'air de 76 et 48 kPa, ou un système de pulvérisation à air assisté à une pression du liquide de 221 et 83 kPa. Un témoin non traité fut aussi inclus pour évaluer l'effet du tébuconazole sur le rendement du soja. Les cartes de papier Kromekote sensible au colorant furent analysée...

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A four-year study was conducted from 2000 to 2004 at eight field sites in Montana, North Dakota and western Minnesota. Five of these sites were in North Dakota, two were in Montana and one was in Minnesota. The sites were diverse in their cropping systems. The objectives of the study were to (1) evaluate data from aerial photographs, satellite images, topographic maps, soil electrical conductivity (EC a ) sensors and several years of yield to delineate field zones to represent residual soil nitrate and (2) determine whether the use of data from several such sources or from a single source is better to delineate nitrogen management zones by a weighted method of classification. Despite differences in climate and cropping, there were similarities in the effectiveness of delineation tools for developing meaningful residual soil nitrate zones. Topographic information was usually weighted the most because it produced zones that were more correlated to actual soil residual nitrate than any other source of data at all locations. The soil EC a sensor created better correlated zones at Minot, Williston and Oakes than at most eastern sites. Yield data for an individual year were sometimes useful, but a yield frequency map that combined several years of standardized yield data was more useful. Satellite imagery was better than aerial photographs at most locations. Topography, satellite imagery, yield frequency maps and soil EC a are useful data for delineating nutrient management zones across the region. Use of two or more sources of data resulted in zones with a stronger correlation with soil nitrate.

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