Earthworm Research


holding an earthwrom

Colorado State University examined 50 earthworm research studies to determine the effect on crop yields. All studies had different crops, soil types, tillage, and fertilizer applications. Overall, healthy earthworm populations increased crop yields an average of 23.3% world-wide. Earthworms thrive in healthy soils and do the best in no-till fields (no tillage), in cover crops fields with good soil organic matter levels, and where crops are rotated. These fields also had higher levels of beneficial bugs, bacteria, and fungi. Earthworms decreased the need for chemical fertilizer by an average of $50/Acre. Earthworms love healthy soils (No-till Farmer, 2024).

Tillage is a major deterrent to earthworm growth. Tillage destroys their burrows, kills some adults but also desiccates earthworm eggs and wipes out future generations. Nightcrawlers are top feeders, using surface residue for food and to maintain soil temperature. Tillage destroys soil organic matter (SOM) which red wigglers need to survive.

To promote earthworms, here are conditions where they thrive. Soil temperature between 50-60OF with pH 5.0 to 8.0, prefer pH near 7.0 or neutral. Moisture soils, not hot or too dry or over saturated and plenty of surface residue to moderate soil temperatures. Night crawlers like low carbon to nitrogen (C:N) ratio crop residue (like hay) and/or solid manure (low NH4+, ammonium) while red wigglers can consume higher C:N ratio with more lignin. Earthworms thrive in fields planted to perennial crops like hay, pasture, legumes or cover crops. Earthworms are a great natural resource and should be promoted to enhanced agricultural fields.

After a 3 to 4 inch rain, farmers should watch where water is ponding or not ponding. In healthy fields with no-till, cover crops, and earthworms; there should be less standing water due to better soil tilth and cleaner water coming off the fields in the surface water or tile. Cover crop roots increase macro and micro-pores where worms live. Earthworms decompose and move the organic residue to form SOM, to keep nutrients and soil in place.

Here is how earthworms improve our soil. They alter soil structure, improving water movement, enhancing nutrient dynamics and plant growth. They are a major soil health indicators, earthworms cannot tolerate poor soil for long periods of time, although they can improve it. Earthworms stimulate microbial activity by inoculating and distributing soil microbes in their casts (earthworm poop). Microbes in the earthworm gut breakdown organic nutrients into plant available forms for enhanced plant growth and worms also secrete plant enhancing growth hormones.

Earthworms turn over the top 6 inches of soil every 10-20 years, while enhancing it, adding SOM that create great soil structure (macroaggregates) for improved drainage. Nightcrawlers move SOM deep into the soil and consume about 1/3 of their weight daily. Red wigglers are slightly smaller, stir the top 3-4 inches of soil, and consume their weight daily in SOM. Red Wigglers are soil inoculators, spreading thousands of beneficial microbes around in the soil that enhance plant growth and yield.

Earthworms can greatly enhance water infiltration and overall soil porosity. In the late 1990’s, researchers thought earthworms might be contributing to phosphorus in Lake Erie. They misinterpreted the data. While earthworms move water and nutrients into the soil, it’s the poor soil structure and lack of live roots that cause nutrients runoff. Live roots absorb P! Adding live roots allows the water to infiltrate both horizontally and vertically, so that the water can then be cleaned and soluble nutrients can be absorbed before clean water exits via tile. Research was done only on no-till fields without a cover crop, so without live roots it failed to intercept and clean the water.

Earthworm burrows can survive for many years if left undisturbed, improving water infiltration and greatly increasing root penetration deep into the soil. The earthworm lines its burrow with castings and SOM, which greatly increases water holding capacity, and slows down the water. The SOM from the cast is high in plant available nutrients. Earthworm burrows are always chocked full of live roots because roots follow the path of least resistance and the roots can absorb the enriched plant nutrients held in the SOM lining the burrow. Mother Nature created this system to keep soluble nutrients in the soil.

Earthworm casts improve the cation exchange capacity (CEC) or how nutrients are stored by a factor of 3-4X. Casts have 3X more phosphorus and potassium, 4.5X more calcium, and 2.5X more nitrogen while improving soil structural stability by a factor of 10X more than the average soil. Earthworms are called soil engineers for this reason and are great indicators of good soil health.