As the phosphate level of the soil is built up, the Gardener may decrease or stop supplementing the manure with bone meal. When organic matter is added to the soil, the Gardener may assume the potassium needs are being met. There is no need to add greensand, wood ashes, granite meal or kainite, which are potassium sources. Micronutrients Iron and zinc are the only micronutrients verified as deficient in Colorado soils. Vegetables most likely to exhibit these deficiencies are corn, potatoes and beans.
Many woody plants are also sensitive to lack of iron and zinc.
Iron deficiency commonly appears as yellow areas between greener veins of young leaves. In zinc deficient plants, leaves and stems often fail to grow to normal size. There also may be yellowing between the veins of leaves, but usually on older leaves. Decomposing organic matter supplies these necessary nutrients. These hold the nutrients in a form available to plants and protect them from fixation in the soil in unavailable forms.