In the past, soil sampling has been used to get farmers “in the ballpark” when it comes to estimating soil fertility.

Procedures like grid sampling often averaged out a lot of the variation and provided fertilization rates that met fertility needs on most of the field. This often led to farmers over- and under-fertilizing many field areas.

Today, new technologies let farmers fine-tune input systems so nutrients can be applied at the right location and rate, or seed at the optimum population.

But to take advantage, growers need a good base of information about variability and characteristics for different fields and field areas. It’s not often you will find these characteristics are completely uniform across an entire field.

Getting Started. If you’re ready to begin using variable-rate fertilizing or seeding, start by determining how variable your fields are by sampling your farm on a 2- to 2½-acre basis.

This step gives you an initial read on field variability and helps you determine how intensively you should sample fields in the future. On highly variable fields, it pays to keep sampling on a 2- to 2½-acre basis, while on more uniform fields you might sample slightly larger blocks.

Getting this detailed information lets you develop fertilizer prescriptions fine-tuned to each field area. These prescriptions will have two components added together.

The first component is nutrients that are needed, or can be credited, based on soil-test results. The second component is nutrients that are needed based on the crop and yield goal…