In order to apply manure correctly, proper soil sampling must be done first. Soil sampling once a year is the key component of a sustainable manure management plan. Different methods of soil sampling exist. When choosing a type, the following points are critical to consider. 1) Select a sampling procedure that will provide information to adjust or support manure application rates and practices, 2) Every field should be sampled every year, and 3) All fields should be sample for a 0-15cm, 15-60cm depth with separate composite samples for each analysis.
The most common method of sampling involves taking random samples throughout the field and once they are thoroughly mixed, a single sample is submitted to the lab. Some points to remember are: 1) avoid sampling in areas of variability, 2) on hilly land, use the mid-slope to get average results, and 3) composite samples should be taken from at least 15-20 sites/field.
Another method is site-specific. Once the variability of the field is understood, it is divided into relatively uniform plots, which are then managed individually. Benchmark sampling is the continued sampling at the same location. Within these same areas, 15-20 samples are randomly collected and analyzed. More than one benchmark area per field may be chosen if variable landscapes occur with the field as this method does not properly address field variability. Grid sampling breaks the fields into smaller grids. It reveals fertility patterns by taking 10-15 samples in each cell. As the intensity of sampling increases the more accurate the fertility patterns will be, but that can add to the cost.