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Fluid Journal : Fluid Journal 1996-1998
2 Fluid Journal Spring 1997 machines, satellite and phone-modem communications are becoming common farm tools. Hand-held, pen-based and voice-activated computers may soon be common tools in the field. Mobile yield monitors, installed in combines, allow collection of site- specific yield data during harvesting. Yields can be displayed and/or stored for later analysis. including the creation of yield maps. Yield maps, such as shown in Figure 1, provide proof, offering: 1) site-specific response data, 2) ground truth for plans and models, and 3) a basis for adjustments in management. Furthermore, GIS applications can be used to create map overlays, which will permit the study of relationships between yield and other mapped attributes such as soil type, soil fertility, weed populations, drainage, and other factors. How a map is generated through SGIS is shown in Figure 2. How to start Record keeping. Begin with a computerized record keeping sy stein. Select a software package that will allow you to organize and link your field data with precise locations within a field. Select a position referencing system such as a latitude-longitude or state plane coordinate system to spatially link all records. Soil test information, nutrient application, and yield records referenced to specific locations within a field are important components of field records. Additional information from photographs and other maps can be digitized into record keeping systems as availability of time and technology permits. Software. Investigate GIS computer software packages that can analyze and display your geo-referenced field data as maps. Consultants or advisers can help in analyzing your computerized records to develop site-specific interpretations for individual fields. Matching right. Farm-level GlS applications are rapidly evolving with several companies devel-oping farm- oriented applications for sophisticated GIS packages currently used in research and education. Figure 2. Generating map via SGIS. Collecting soil samples Sample collection is the most critical part of soil testing for developing variable rate fertilizer application maps. Research is under way on how to optimize sampling for various combin-ations of soil properties, cropping systems, and fertilization/ manuring histories. For example, it is likely that sampling requirements in the unglaciated Great Plains, where neither manuring nor fertilizing has been done extensively, will be less intensive than in the heart of the Corn Belt. Grid pattern. Research in Wisconsin and Illinois has resulted in the following suggestions: • overlay field with a grid • for initial sampling, make each grid cell no larger than one acre unless field has a history of high soil test values and fertilizer applications in excess of normal crop removal (in the latter case, a two-acre cell may be acceptable) • sample portions of the field on a finer grid if responsive sites are identified with the first sampling pass • perform future sampling of fields by using a larger grid size or by nutrient management areas, depending on the outcome of the initial sampling • locate sample point by counting rows and measuring distances, or, prefer-ably, navigate to the point using GPS • give preference to a systematic but unaligned pattern (especially if GPS referencing is available) over taking samples in straight rows across fields that may be biased by previous management such as fertilizer application patterns • collect at least 5 to 8 soil cores for each grid cell, taking the cores from within a radius of 10 feet of the sample point. Uniform depth. Soil tests are usually calibrated on the basis of an acre furrow slice---approximately two million pounds of soil. Check with your lab for its recommendation on sampling depth, because some labs use their own calibration data set that is based on a sampling depth different from the 6-2/ 3-inch standard. For no-till fields, consider collecting a set of samples at the standard depth and another set to represent the top two inches. This will help identify stratification of nutrients, and is especially important for pH determination. Commitment Every farmer should develop a strategic plan that works toward detailed, site-specific nutrient management.
Fluid Journal 1993-1995
Fluid Journal 1999-2001