Composite sampling can be greatly improved if used with an electrical conductivity (EM) soils map. EM mapping accurately defines the NRCS soil information and allows for cores to be taken in the primary area of the zone. Today’s intense data collection by EM is much superior to the old hand analysis method of creating maps. The information provided with the NRCS maps is most valuable in defining productivity soil composition and other relevant agronomic information.
After determining the precise location of soil types from the EM map, geo-referenced soil collections are placed, avoiding transitional soils or minor areas in predominant soil types. For better consistency from one soil sampling cycle to the next, having the geo-referenced points to go back to is necessary, since nutrients can be variable even in the same soil type.