Organic matter has a large influence on soil structure. Good soil structure improves aeration and water movement and retention. This encourages increased microbial activity and root growth, both of which influence the availability of nutrients for plant growth. Soil organic matter also affects the availability of plant nutrients and how pesticides react in the soil. Soils high in organic matter tend to have a greater supply of plant nutrients compared to many soils low in organic matter.
Organic matter tends to bind up some soil pesticides, reducing their effectiveness.
Tests for micronutrients are usually not performed unless there is reason to suspect a problem. Certain plants have greater requirements for specific micronutrients and may show deficiency symptoms. Iron deficiency is common on blueberries, rhododendrons, and pin oaks unless the soil is quite acidic. On these plants, the younger leaves will usually show signs of the deficiency first. The areas between the veins will be yellowish while the veins remain green.