Humic Acids vs. Compost

Two of the most common methods used for rapidly increasing soil organic matter and improving soil biology are to add compost or to add humic substances. There are pros and cons with each.

Compost that is created on or near the farm from local source materials and using local microorganisms for the composting process is always the very best approach, when possible and practical. However, though homemade compost is rich in organic material, it is labor intensive and requires very large amounts (up to 5 tons/acre). A benefit is that the microorganisms responsible for composting the source material can travel along with the compost into the field. If compost is purchased rather than made on the farm, it can be difficult to know exactly what
went into the making of it. If manures were incorporated, there may be undigested weed seeds and harmful bacteria present. Grass clippings may contain herbicides. Carbon and nutrient content will vary quite a bit depending on the source of the composted materials. Compost is bulky and can be difficult to transport and apply—and it can only be applied during times when crops are not growing in the field. Once applied, it may take further years to decompose before it fully adds to the soil humus. At an average cost of $60/ton, it can cost about $300/acre to apply (before transportation charges, if any).

Humic substances on the other hand (technically humic and fulvic acids) must be mined and purchased. As a residue of plant and animal matter that has been created over millions of years (from heat and pressure, much like coal), humic substances contain high amounts of carbon and nutrients and will add directly to soil humus. Liquid versions can be applied at any time during the crop season, and liquid or dry material will be relatively sterile in terms of bringing along additional microorganisms. Research has consistently shown that humics improve root mass and growth, enhance nutrient availability and uptake, and contribute to higher crop yield and quality. Though more expensive than compost ($500/ton), much smaller amounts per acre are required (150–200 lb/acre), resulting in a much smaller cost per application of about $50/acre.

Here is a Comparison Overview:

Soil Humus Levels

Humic Acids: Significant, long-lasting addition of carbon, directly adding to humus levels. Mined humic substances have 60%–70% humic/fulvic acids.

Compost: Rapidly decomposes, leaving minerals behind but releasing carbon into atmosphere as CO2. Good quality compost has about 5% humic/fulvic acids.

Nutrients

Humic Acids: Will help existing nutrients to become mobile within the soil. Increases availability of P. Stabilizes N. Acts as a chelate complexing agent for N & P.

Compost: Minimal effect on existing soil nutrients. May add about 1.5 lb of N, 1 lb P, and 1 lb K per ton of compost. Inconsistent nutrient levels (depending on source material). No chelating effects.

Soil Biology

Humic Acids: Improves microbial diversity. Stimulates beneficial microbes. Does not contain microbial life.

Compost: May bring new microorganisms / pests / pathogens / undigested seeds to the soil.

Soil Health

Humic Acids: Rapidly enhances soil structure. Detoxifies soils. Buffers soils from effects of heavy metals.

Compost: Slowly enhances soil structure. No detoxification effect. No buffering effect (may add heavy metals).

Consistency

Humic Acids: Highly consistent and stable carbon source.  

Compost:  Not consistent—dependent on source material (may contain varying carbon, nutrients, weed seeds, bacteria levels).

pH, CEC, Salt Levels

Humic Acids: Neutralizes pH. Increases CEC (average is 800–1,200; 10x to 20x over compost). Buffers salt.

Compost: May raise or lower pH. Minimally increases CEC. May add salt.

Biostimulant Activity

Humic Acids: Concentrated biostimulant effect.

Compost: Diluted and highly variable biostimulant effect.

Water-Holding Capacity

Humic Acids: Lasting, high water-holding capacity. Holds up to 7x water weight.

Compost: Water-holding capacity is high, but it diminishes over time.

Health & Safety

Humic Acids: No health or safety concerns.

Compost: May contain harmful bacteria, causing plant- or soil-borne diseases. May contain herbicides or pesticides.

Application

Humic Acids: Liquid versions can be applied at any time in the crop season.

Compost: Bulky to transport and apply. Can only be applied when no plants are in the field.

Application Cost

Humic Acids: 200 lb/ac @ $500/ton = $50/ac (less is required if liquid versions used, may change costs).

Compost: 5 tons/ac (or more) @ $60/ton = $300/ac (or more). Delivery may be an additional per-mile cost.

To download the Humic Acids vs. Compost Comparison Guide, click here.

For more information about Huma Gro^® Humic and Fulvic Acids, click here.