Grid sampling is a favored method for site specific soil management because it is unbiased, simple, relatively quick and software exists to facilitate it. After the samples have been pulled, georeferenced and analyzed, a map is made by either filling in the grid cells with the soil test value (grid cell method) or assigning the soil test value to a point and then interpolating between points (grid point method). Grid sampling results in either a "checkerboard" map (grid cell method) or a "smoothed" map (grid point method).

Improving Grid Sampling:  Simple steps will improve the quality of a grid sampling plan.

• Use an unaligned sample design to minimize systematic errors.
   Pay attention to each individual sample pattern as you do to an overall grid pattern. Increase the sample radius for each
   point to 25% of the sample distance (80 ft. radius for 2.5 acre grids).
• Increase or decrease grid sampling intensity based on prior knowledge of variability within separate field regions.

When applying fertilizer based on the sample pattern, incorporate strip plots with fertilizer recommendations based on a separate whole field soil sample. This allows an on-site evaluation of the effectiveness of the grid design and fertilizer application.

Beyond Grids—Directed Sampling:  Using "directed" sampling avoids many of the problems of grids. In directed sampling, a field is broken up into an appropriate number of regions which are sampled individually. The shape and size of each region are based on the variability present within the field and the intensity of management considered necessary and practical. To formulate an appropriate directed sampling pattern, prior knowledge about the spatial patterns present within a field must exist. Useful sources include:

• Farmer experience
• SCS soil maps
• Past yield maps
• Past grid sample maps
• Topography maps
• Aerial field imagery
• Management history maps