1. Random Composite Sampling
Random composite soil sampling involves taking samples in a random pattern across a field, avoiding problem areas.
This sampling is most suitable for fields less than 80 ac, that have been uniformly cropped in the recent past and have little natural variation.
For random soil testing, we collect cores from 20 to 30 sites and separate each core by depth to acquire representative composite samples for each depth.
2. Directed Random Composite Soil Sampling
Directed random soil testing is a modified form of random soil sampling.
This sampling pattern is preferred on fields where it is challenging to identify a single dominant area that would represent most of the field. The field is sub-divided into management zones based on unique characteristics (i.e. yield management zones, organic matter, topography, salinity etc.)
One field may require several composite samples depending on the number of management areas.
3. Benchmark Sampling
Benchmark sampling uses small (ex. 30 m by 30 m) representative sites on a field to guide fertilizer recommendations for the entire field.
This sampling methodology involves sampling site in a grid pattern to prepare a composite sample for each soil depth. These sites are marked with GPS, so that sampling can occur from the same small area after each year, reducing sampling variability and identifying yearly changes in soil nutrient levels.
4. Directed Benchmark Sampling
Directed benchmark sampling involves establishing multiple benchmark areas and management zones, based on unique soil characteristics.
This approach can be applied when major areas of fields have distinct features that can be managed individually. Management zones can be identified using soil surveys, elevation maps, yield maps or remote sensed images.
5. Grid Sampling
Grid sampling is the most intense and expensive sampling strategy.
This sampling uses a systematic approach in identifying fertility patterns and presumes topography is not an underlying factor in soil fertility patterns within a field.
For grid sampling, a field is divided into many small areas which are sampled typically 3 to 10 times. The sampling frequency may range from one sample from each 0.5 ac area to one sample from each 5 ac of the field.
