How to Manage Pests

The UC Guide to Healthy Lawns

Fertilizers vs. soil amendments

Fertilizers improve the supply of nutrients in the soil, directly affecting plant growth. Soil amendments improve a soil's physical condition (e.g. soil structure, water infiltration), indirectly affecting plant growth.

The terminology used in describing fertilizers and soil amendments is confusing. The definitions below explain some common concepts.

On this page:

Soil amendments
Synthetic fertilizers vs. natural organic fertilizers

Quick release vs. slow release fertilizers
Fertilizer-pesticide combination products

Soil amendments

Photo of organic and nonorganic amendmentsOrganic amendments
Organic soil amendments modify the soil structure as they decompose, allowing it to absorb and retain water and nutrients more efficiently. Soil-borne insects, worms, fungi, and other organisms help decompose organic material, but require energy from available nitrogen in the soil to do so. For this reason, the soil must often be augmented with nitrogen when undecomposed (not composted) organic amendments are applied. Many products classified as natural organic fertilizers are also organic soil amendments.

Examples: hay, straw, peat moss, leaf mold, and sawdust

Nonorganic amendments
Gypsum is an example of a nonorganic amendment added to soil to improve water infiltration on high-sodium soils.

Synthetic fertilizers vs. natural organic fertilizers

Synthetic fertilizers
Synthetic fertilizers are chemically manufactured materials containing one or more of the primary nutrients necessary for plant growth: nitrogen, phosphorus, and potassium.

Natural organic fertilizers
Natural organic fertilizers are derived from either plant or animal products containing a significant quantity of one or more of the primary nutrients necessary for plant growth: nitrogen, phosphorus, and potassium. Nutrient content must be labeled on the package. Most natural organic fertilizers also provide significant quantities of organic matter, so they can also be classified as soil amendments.

Examples: manures, sewage sludge, and bone meal

Quick release vs. slow release fertilizers

Photo of organic and synthetic fertilizersQuick release fertilizers
Quick release fertilizers, also known as "fast-acting" fertilizers, are water soluble chemicals that once applied are readily available to the plant. If properly applied, plants green up quickly. However, if too much is applied, quick release fertilizers have a tendency to burn turf. These materials are easily leached with rain or over-irrigation and require frequent application. They are the least expensive fertilizers and are always synthetic products.

Examples: ammonium nitrate, ammonium sulfate, calcium nitrate, and urea

Slow release fertilizers
Slow release fertilizers, sometimes called water-insoluble types, release nitrogen over time. They are often applied at higher rates and less frequently than quick release formulas. The initial response of turf is slower than quick release types but these materials continue to provide nutrients over a period of 8 to 10 weeks or more. They will not burn the turf even if applied at high rates and are not prone to leaching. These products are a little more expensive and include certain synthetic fertilizer products and all natural organic fertilizers.

Examples: sulfur-coated urea, urea formaldehyde, Isobutylidene diurea (IBDU), and organic fertilizers

Slow release-quick release mixtures
Some fertilizers are formulated with both water insoluble (slow release) and water soluble (quick release) nitrogen. Plants green up quickly and continue to receive nutrients over a period of time. For the most effective product, at least one-fourth of the nitrogen should be in the water insoluble, or slow release form.

Fertilizer-pesticide combination products

Some fertilizer products contain a herbicide or insecticide for weed or insect control. However, pesticides are often not warranted at the time fertilizer is applied. Avoid these combination materials and apply pesticides separately and only if needed.

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