Compost and Humate Testing

For compost and humate testing download and complete this form:

Compost / Humate Test Form

See Explanation of Soil Organic Matter here.

See Example of Humate Test Results here.

Compost Testing and Organic Mix Testing

Composting testing is important for characterizing the beneficial physical and chemical properties of a compost as well as for identifying potential problems with compost use. Texas Plant and Soil Lab employs testing procedures from the U.S. Compost Council’s Test Methods for the Examination of Composting and Composts as well as some proprietary testing methodology that is also essential to measure the quality of your compost.

For example, Texas Plant and Soil Lab measures the humus fraction of the compost as well as the total organic matter to verify that the compost is fully mature. An indicator of compost maturity is high OM (humus) and Nitrate (NO3) > 30 ppm which indicates well matured (cured) compost by biologically active microbes releasing Nitrate (NO3). High OM (humus) and Nitrate (NO3) < 10 ppm indicates a very active to moderately active (curing stage) compost. Adjusting C : N ratio with fertilizer N or biologically with energy (molasses, fish, vegetable meals, etc.) will aid maturity. Just like a conventional fertilizer bag that comes with a guaranteed analysis and a label rate, we must also know the guaranteed analysis of composts to make sure that we apply safe rates to avoid accumulation of excessive mineral salts over time.

General Guidelines of Compost Testing and Organic Mix Testing

pH is a measure of active acidity in the feedstock or compost. Most finished composts will have pH values in the range of 5.0 to 8.5. Ideal pH depends on compost use. A lower pH is preferred for certain ornamental plants while a neutral pH is suitable for most applications. pH is not a measure of the total acidity or alkalinity and cannnot be used to predict the compost effect on soil pH.

Soluble salts are determined by measuring Electrical Conducity (EC) in a 1:5 (compost:water, weight ratio) slurry. Electrical Conducity (EC) is related to the total soluble salts dissolved in the slurry and is measured in units of millimhos/cm (mmho/cm). Composts typically range from 1 to 10 mmhos/cm. High salinity may be toxic to plants. Ideal soluble salt levels will depend on the end use of the compost. Final compost blends with soil or container media/potting mixes should be tested for soluble salts.

The ideal moisture content for composting will depend on the water holding capacity of the materials being composted. In general, high organic matter materials have a high water holding capacity and a higher ideal moisture content. A typical starting compost mix will have an ideal 65-45 % mositure. Finished compost should have a 50-40 % moisture.

Compost Testing and Organic Mix Testing Protocols

Compost Basic Analysis is recommended as an initial test for feedstock to help determine appropriate mixing ratios. This test may also be used as a basic test for finished composts although nutrient testing on finished composts is recommended.

The Compost Standard Analysis includes the Basic Analysis plus Total Nutrients, recommended for feedstock and finished composts that may contain heavy metals and other pollutants.

Compost Standard Analysis plus Heavy Metals includes all analyses plus the EPA 503 pollutants: Arsenic (As), Cadmium (Cd), Copper (Cu), Lead (Fe), Mercury (Hg), Molybdenum (Mo), Nickel (Ni), Selenium (Se), and Zinc (Zn). This compost testing is very important especially if using a biosolid as a source for the compost

Compost Comprehensive Analysis includes an additional test for PCBs, Plant Response (% Germination), Fecal Coliform and satisfies the requirements of TxDOT, General Permit, Sewage Sludge Quality Test. The tests for the U.S. Compost Council STA program provide the analyses required for producers involved with the Compost Council’s Seal of Testing Approval (STA) program.

Please contact us today at 956-383-0739 and speak with us
about your needs.