Submitted to: Potash and Phosphate Institute Guides
Publication Type: Popular Publication
Publication Acceptance Date: 12/23/2002
Publication Date: N/A
Technical Abstract: Soil fertilizer recommendations in modern crop production rely on laboratory analysis of representative soil samples. Regardless of where the samples were collected (grid points, management zones, or whole fields), the accuracy and precision of the fertilizer recommendation can be improved by considering the factors that influence nutrient variability. As each producer's crop production enterprise varies, it is recommended that producers select approaches suited for their operation. The objectives of this guide are to discuss how management influences nutrient variability and to provide insight into designing a soil sampling protocol that will provide good fertilizer recommendations. The accuracy of the fertilizer recommendation is improved by increasing the number of individual cores included in a composite sample. In tilled fields where N and P fertilizers were broadcast, a good sampling strategy is to randomly collect between 15 to 30 individual soil cores from each sampling zone. A composite sample should always contain at least 15 individual cores. Sample areas where animals were confined separately from the rest of the field. Evidence for old homesteads and animal confinement can be seen in USDA-NRCS aerial photographs collected during the 1950s and 1960s. When possible, avoid sampling guess rows as they may contain none or two fertilizer bands. In a reduced tillage system where nutrients were band applied, keep records on how, when, and where they were applied. Specific guidelines for sampling residual bands are described further in the guide.