What’s in this publication?
This publication focuses on how to design a soil nutrient monitoring strategy that fits today’s requirements for recordkeeping and increased accuracy in managing nitrogen (N), phosphorus (P) and other nutrients. We advocate the use of management units or zones for soil testing and nutrient application. To measure a real change in soil test values over time, you will need to use consistent management units over many growing seasons.
In this publication, a management unit is considered an area in a field that is soil-sampled and fertilized separately for one or more nutrients. Different management unit delineations may be more appropriate for insect, weed and disease control; irrigation water management; and other cultural practices.
The management unit approach is designed to provide better information to make nutrient management decisions at a reasonable cost. This approach combines the ease of traditional whole-field sampling and the power of an intensive grid sampling method. With a management unit approach, a grower can vary the amount and type of nutrient applications within a field without the need for grid sampling.
A monitoring strategy will answer only the questions it was designed to answer. Each field will have a specific soil sampling strategy. Key questions to consider when developing a soil testing strategy for nutrient management are discussed in this publication, including time of sampling, depth of sampling, number of subsamples and location for sampling in the management unit.
A soil sampling protocol designed to measure changes in soil nutrient status over time must minimize random variability in soil test results. This is especially important when soil sampling is part of a required nutrient management plan. This publication suggests strategies for minimizing random variability.
Two examples of nutrient monitoring are provided to illustrate the process of deciding when, where and how to sample, as well as how to interpret the soil test results. One example uses reference sampling areas within management units, and the other uses random sampling throughout the management unit. These examples are intended to illustrate the process of using management units to make nutrient management decisions.