Estimates of the economic impact of sprayer skips are complicated because influence of weed control on crop yield varies by crop. For example, the weed popula¬tion and long-term weed seed-bank effects have to be evaluated and assessed. For fertilizer and lime appli¬cation, how much yield is lost if the area receives no application? A skip is much more costly in a higher-value crop, such as vegetables or seed crops, than it would be in a bulk commodity such as corn, soybeans, or wheat. If the skip occurs in a very clean field, the yield-loss effect due to reduced weed control may be minimal, but in a heavily infested field, the yield may drop to almost zero in the skipped area. Weed scientists suggest that the greatest economic effect of skips may be the creation of a seed bank that will lead to man¬agement problems and greatly increased weed control costs in future years. Similarly, for a field at pH 5.8, the yield loss due to skipping an area with lime application will probably be small during the first year, but will become greater in later years.
Bottom Line
GPS navigation has many advantages over conven¬tional marking devices such as foam markers, and especially over the visual-estimation method for spin¬ner spreaders. With an existing GPS being used for yield monitoring or field mapping and soil sampling, the GPS navigation system can increase the efficiency of the farm or agribusiness while minimizing adverse environmental impacts associated with overlapping applications. The system can also reduce operator fatigue and anxiety regarding fertilizer and pesticide application. Finally, use of this technology can demon¬strate to the nonagricultural community that advanced technology is being used to farm efficiently and safely. The advantage of “as-applied” maps, provided by some systems, is documentation that applications were made at the appropriate location and rate.