Top Soil EM Mapping
The following maps are from Northwest Iowa.
The maps shown above display the correlation that an accurate soils map has with yield. Some of the reasons for this could be characteristics, such as water holding capacity of the soil, basic productivity of the soil and emergence problems due to soil characteristics. As a general rule, EM soil maps in the MISS trade area correlate closely with yield maps as the second set of figures also show. Therefore, using EM soil maps are a very useful tool in agronomic management for change of seeding rates, using different varieties of seed, applying different amounts of chemical or fertilizer or any situation that calls for soil information. The USDA/NRCS maps are still very valuable for providing information on productivity, permeability and other soil type characteristics.
Generally, the lower the EM reading the more sand content and, thus, poorer water holding capacity. The higher the reading, the more clay content and higher water holding capacity; therefore, the soil is usually more productive. However, especially in glacial till soil, the highest readings are not necessarily the most productive. These soils can have very fine clay particles that have very poor internal drainage, causing lower productivity from denitrification in wet soils and poor root penetration.
Subsoil EM Mapping