Benefits of Wool Pellet Fertilizer Across Crops and Soil Type

Wool pellet fertilizer (made from compressed sheep’s wool) is gaining attention as a sustainable soil amendment and nutrient source. Below we present findings on its effects across various cash crops, its benefits in different soil types, its nutritional makeup, and other agronomic/environmental advantages. Supporting data from scientific studies and agricultural trials are included.

1. Effects on Different Cash Crops

Wool pellets have been tested on a range of crops – vegetables, fruits, grains, and others – with generally positive outcomes. Table 1 summarizes key effects observed in different crops, followed by detailed examples:

Table 1. Reported Effects of Wool Pellet Fertilizer on Various Crops

Crop	Observed Effects with Wool Pellets	Source
Tomato (vegetable)	Yields comparable to standard organic fertilizer when applied at equal N rates; ~60–70% higher fruit weight vs. unfertilized controlextension.sdstate.edu. No negative effect on fruit qualitywoona.hr.	Bradshaw & Hagen 2022projects.sare.org; Ordiales et al. 2016woona.hr
Spinach (leafy veg)	Yield and growth similar to commercial organic fertilizer at equal N; significantly higher yield than unfertilized (3× increase)uvm.edu. Nutrient uptake (K, Mg, P, S, B, Ca) in leaves showed some differences but no consistent deficiency or excessprojects.sare.org.	Bradshaw & Hagen 2022projects.sare.orgprojects.sare.org
Lettuce (leafy veg)	Improved growth in multiple soil types: in a pot study, 10 g/L wool pellets increased plant fresh weight 2.5×, leaf count 1.4×, and height 1.4× compared to no fertilizerupdatepublishing.com. Wool pellets raised leaf tissue N and K content ~1.4× and boosted yield especially in sandy and clay soilsupdatepublishing.comupdatepublishing.com.	Correa et al. 2025updatepublishing.comupdatepublishing.com
Broccoli (vegetable)	Highest wool pellet application (≈200 kg N/ha) produced maximum broccoli head yield under organic conditions, matching conventional yield benchmarkswoona.hrwoona.hr. No adverse effect on head quality was observedwoona.hr.	Ordiales et al. 2016woona.hrwoona.hr
Maize (grain)	Wool pellets (1% by soil weight) provided sufficient slow-release N to fully meet maize’s needs in a sandy loam, resulting in high biomass without additional fertilizerlink.springer.comlink.springer.com. Excess mineral N did not further increase yield, indicating efficient N supply from woollink.springer.com.	Abdallah et al. 2019link.springer.comlink.springer.com
Sunflower (oilseed)	Low-to-moderate wool pellet rates (≤1% w/w) enhanced growth rate and biomass. Highest biomass and flower yield achieved with optimal wool dose (carbonized wool performed best) link.springer.comlink.springer.com. Wool fertilizer at 2% had slight diminishing returns in some cases.	Abdallah et al. 2019link.springer.comlink.springer.com

Vegetable Crops: Multiple studies confirm that wool pellets can sustain or improve yields in vegetables. For example, tomatoes and spinach fertilized with wool pellets produced yields equivalent to those with standard organic fertilizer when the same amount of nitrogen was applied projects.sare.org. In trials at the University of Vermont, wool pellets at a nitrogen rate matching the grower’s usual fertilizer yielded no significant differences in tomato fruit yield or quality compared to the commercial fertilizer projects.sare.org. Both fertilizers increased yields substantially over unfertilized controls; one report noted tomato fruits were 58–69% larger with wool pellet fertilizer than with no fertilizer at allextension.sdstate.edu. Wool pellet treatments in spinach similarly tripled the yield over unfertilized plotsuvm.edu. In a Spanish field study on processing tomato, the highest wool pellet dose (approx. 200 kg N/ha) gave the highest tomato yield under organic conditions woona.hr. Notably, these high yields were achieved without compromising fruit quality (sugar, acid, and other quality parameters were unchanged by wool vs. other fertilizer)woona.hr.

Other vegetables respond well, too. Lettuce grown in pots with wool pellets showed dramatically improved growth: at 1% wool (10 g/L), lettuce had 2.5 times greater fresh weight and ~40% more leaves than unfertilized plantsupdatepublishing.com. Researchers in Chile found wool pellets improved lettuce performance especially in nutrient-poor sandy and clay soils, by steadily releasing nitrate and potassium and keeping the root zone moist updatepublishing.comupdatepublishing.com. Wool-fed lettuce leaves had higher N and K content, indicating enhanced nutrient uptake updatepublishing.comupdatepublishing.com. Similarly, field trials in Vermont and Canada have reported that wool pellets can match or exceed standard fertilizers for vegetables like broccoli, peppers, and spinach in terms of yield woona.hr. For broccoli, wool pellets applied at ~2000 kg/ha (supplying ~200 kg N) yielded profitable head yields comparable to conventional fertilization, with no difference in broccoli head quality metrics woona.hrwoona.hr. Overall, vegetables that are heavy feeders (tomato, broccoli, leafy greens, etc.) benefit from wool’s slow nitrogen release, which supports steady growth and often yields that are equal or superior to traditional fertilizer programs projects.sare.orgextension.sdstate.edu.

Wool pellets may also contribute to healthier root systems in vegetable crops. As the wool fibers in the pellet break down, they swell and create porous channels in soil, improving aeration (oxygen flow) around roots wildvalleyfarms.com. For crops like tomatoes that prefer consistent moisture, the water-holding ability of wool can prevent drought stress and promote robust root development. In one study, tomato plants given higher wool pellet rates grew larger root systems and more robust foliage, correlating with greater fruit output, thanks to the continuous moisture and N supply in the root zone fermesleystone.comwildvalleyfarms.com. Garden trials also note that wool-amended soil is “breathable,” which promotes healthy root development and nutrient uptake for vegetables wildvalleyfarms.com.

Fruit Crops: There is emerging interest in using wool pellets in fruit orchards and vineyards, though published yield data are still limited. Wool’s ability to conserve soil moisture and supply nitrogen over time is likely advantageous for fruit trees and vines. Initial experiments in olive cultivation (potted olive saplings) showed that adding wool residues significantly improved shoot growth without harming soil microbes or mycorrhizaebioresourcesbioprocessing.springeropen.combioresourcesbioprocessing.springeropen.com. In that study, moderate wool application increased olive stem diameter, suggesting better vigor, whereas only extremely high dosages had any negative effects (e.g. slight reduction in root mycorrhizal colonization at 2% wool)bioresourcesbioprocessing.springeropen.combioresourcesbioprocessing.springeropen.com. Wool-based mulches and pellets have also been tested in apple orchards and vineyards to improve water retention and provide slow nutrition; these treatments are reported to maintain fruit yields while reducing irrigation needsengagement.source.colostate.edufermesleystone.com. Furthermore, commercial products combining wool with other organic matter are marketed for fruit trees – for instance, one sheep-wool fertilizer is labeled as a “base fertilizer for all garden, fruit, and vegetable plants,” owing to its balanced nutrient supplycompo.com. While specific fruit yield increases are not widely documented yet, practitioners observe that wool pellets can support fruit crop growth (e.g. citrus, berries) by releasing nitrogen during critical growth stages and buffering soil moisture in drought-prone orchardsengagement.source.colostate.edu. Given that wool pellets supply nutrients without excess phosphorus, they can be useful in perennial fruit systems where P buildup is a concern (e.g. grape vineyards in high P soils)fermesleystone.comfermesleystone.com. In summary, wool pellets are considered suitable for fruit crops, and ongoing trials aim to quantify their effects on fruit yield and quality under field conditions.

Grains and Field Crops: Wool pellet fertilizer has demonstrated benefits for grain and other field crops. Maize (corn) and sunflower are notable examples. In a controlled pot experiment on a sandy-loam soil, adding just 1% wool pellets to the soil enabled maize to grow vigorously without any additional fertilizer – the wool provided enough nitrogen such that maize biomass was as high as or higher than maize receiving full-rate mineral N fertilizerlink.springer.comlink.springer.com. Notably, maize with wool alone outperformed maize that received wool + excessive mineral N, indicating wool’s N release was sufficient and that adding more N was unnecessary or even inhibitorylink.springer.com. For sunflowers, wool amendments increased plant height, leaf number, and flower yields at moderate rates; the best growth was observed with a carbonized wool pellet at ~1% of soil weightlink.springer.comlink.springer.com. A slight decline at 2% wool in some cases suggests extremely high wool concentrations may transiently immobilize some nutrients or affect soil osmotics, but low-to-medium doses consistently improved biomass productionlink.springer.com.

Other field crops have shown positive responses as well. A recent study in Poland on winter wheat found that waste wool fertilizer can be successfully used in wheat cultivation, contributing to plant nutrition without negative effects (wool is fully biodegradable over the season)extension.sdstate.edu. Similarly, research in India on cluster bean (Cyamopsis), a legume, reported that wool amendments enhanced soil fertility and raised macro- and micro-nutrient levels in both soil and plant tissuesmdpi.com. In that trial, clusterbean plants fertilized with raw wool grew more vigorously and had higher concentrations of nutrients like N, P, Zn, etc., compared to unfertilized controls, demonstrating improved nutrient uptakemdpi.com. Experiments with asparagus in Slovenia found that sheep wool pellets (and even wool mixed with leather waste) could serve as effective fertilizers in organic asparagus production, maintaining spear yields while adding organic matter to soilsmdpi.commdpi.com. A diverse range of plants – from herbs and forages (basil, peppermint, ryegrass) to ornamentals (marigold, valerian) – have been tested with wool-based fertilizers, generally showing improved growth, higher biomass, or larger yields relative to no-fertilizer controlsbioresourcesbioprocessing.springeropen.com. This broad efficacy is attributed to wool’s gradual nutrient release and soil-improving properties, which benefit many plant types.

Fiber Crops: There is less published data specifically on fiber crops like cotton or hemp, but the high-nitrogen content of wool pellets suggests they could similarly boost such crops. Cotton, for example, has high nitrogen needs; using wool pellets could potentially supply those needs organically. In general, wool pellets are promoted as suitable for “all crops” that require nutrients and improved soil moisturewoona.hrcompo.com. Anecdotal reports from growers indicate better cotton seedling establishment when wool pellets are mixed into transplant soil (due to improved moisture retention and fertility), though formal studies are still ongoing. Given that wool pellets have been proven on diverse vegetable and grain crops, it is likely that fiber crops would respond with improved growth and yield as well, provided the wool is applied at appropriate rates. In fact, one long-term benefit for fiber or biomass crops is that wool’s nutrient release can span multiple months or even into the next growing season (since not all fibers decompose in one year), potentially supporting sustained growth of perennial fiber crops. As research expands, we expect to see documentation of wool pellet fertilizer in cotton, hemp, flax, and other fiber crop production.

2. Benefits for Various Soil Types

Beyond supplying nutrients, wool pellets act as a soil conditioner, offering distinct advantages in different soil types. Whether the soil is sandy, clayey, loamy, acidic, or alkaline, incorporating wool pellets can improve water relations, structure, and biological activity:

• Water Retention: Wool fibers can hold remarkable amounts of water relative to their weight, helping soils retain moisture. In sandy soils, which normally drain quickly, wool pellets serve as miniature sponges: studies show wool can hold anywhere from 3.5 times up to 20–30 times its weight in water, depending on the wool’s processingwoona.hrextension.sdstate.edu. Once soil microbes degrade the wool’s natural lanolin (a water-repellent wool grease), the fibers readily absorb water like a spongecompo.com. Dry, arid soils benefit greatly – in a tri-soil experiment (sand, clay, peat), adding wool pellets raised soil moisture by 3% to 25% (absolute increase) compared to unamended soil, especially during dry periodsupdatepublishing.comupdatepublishing.com. This extra moisture kept plants alive and productive under drought stress. By acting as moisture reservoirs, wool pellets buffer plants against both drought and flooding. During heavy rain, swollen wool pellets temporarily soak up excess water, preventing waterlogging and root rot; later they slowly release that water back to plants as the soil driesfermesleystone.comfermesleystone.com. In times of drought, the stored moisture provides a more consistent supply to roots, reducing wilting and irrigation requirementsfermesleystone.comfermesleystone.com. For example, greenhouse tests found that potted plants with wool in the mix required watering less often, yet maintained higher transpiration (plant water use) because evaporation from soil was reducedextension.sdstate.eduextension.sdstate.edu. The net effect is improved water-use efficiency: more of the water stays available to plants rather than draining away or evaporating. This is particularly valuable in sandy or loamy-sand soils and in regions facing drought or irregular rainfall.

  
  

• Soil Structure & Aeration: Wool pellets improve the physical structure of both heavy clays and light sands. As the pellets absorb water and swell, they expand within the soil pore spaces, pushing soil particles apart and loosening compacted zonescompo.comwildvalleyfarms.com. In clay soils, which tend to be dense and poorly aerated, this swelling action increases porosity and reduces bulk density. One study observed that amending a hardsetting sandy loam with 2% wool residue decreased soil bulk density by ~10–12%, indicating a lighter, fluffier soil structureewemass.orgd-nb.info. Improved porosity means better root penetration and more oxygen in the root zone, as wool-created voids enhance gas exchange. Plant roots grow more extensively in such conditions, and beneficial aerobic microbes thrive. In sandy soils, wool fibers help bind loose particles and improve aggregationmdpi.commdpi.com. By adding organic fibers, the soil gains structure and stability, which helps it hold nutrients and water better. Farmers in Utah have noted that wool pellets improve soil tilth, making it crumblier and easier to workmdpi.com. The Utah Farm Bureau reports wool acts as a soil conditioner, improving water holding and bulk density while also encouraging aggregation of soil crumbsmdpi.com. Overall, wool pellets contribute to a friable, well-aerated soil ideal for root growth. Increased aeration not only boosts root respiration and depth but can also mitigate issues like root diseases in waterlogged clay by preventing anaerobic conditions.

  
  

• Microbial Activity: As an organic amendment, wool pellets feed and stimulate the soil’s microbial community. Soil organisms (bacteria, fungi, earthworms) are activated by the addition of carbon-rich, nitrogen-rich wool. Microbes gradually break down the keratin in wool, and in doing so they multiply and produce enzymes that further improve soil healthcompo.comcompo.com. Research has shown that wool amendments can increase microbial biomass and activity similarly to other organic inputs. For instance, after wool pellet application, soils showed elevated levels of nitrifying bacteria as the wool’s nitrogen became available. An experiment in Italy with olive tree pots found no negative impact on soil bacterial diversity from wool; in fact, certain beneficial bacterial groups (e.g. genera involved in nutrient cycling) became more abundant in wool-amended soilbioresourcesbioprocessing.springeropen.combioresourcesbioprocessing.springeropen.com. Wool also did not inhibit arbuscular mycorrhizal fungi (AMF) at moderate rates – mycorrhizal colonization of roots remained high, indicating that these symbiotic fungi can coexist with wool and help plants absorb nutrientsbioresourcesbioprocessing.springeropen.combioresourcesbioprocessing.springeropen.com. The gradual decomposition of wool provides a continuous food source for microbes, supporting a rich soil food web. Farmers often observe an increase in earthworm activity in wool-treated plots, as the wool softens the soil and provides organic matter. Active soil biology translates to better nutrient mineralization – microbes turn the wool’s organic N into ammonium/nitrate and make other nutrients more plant-available. Additionally, healthy microbial populations can help suppress soil-borne pathogens and improve disease resistance (by competition and by inducing plant immune responses). While research is ongoing, preliminary evidence suggests wool amendments may contribute to a more disease-suppressive soil environment over timewoona.hrwoona.hr. (This is in line with general benefits of organic matter: one cited benefit of keratin-rich amendments is that they “suppress diseases and induce biochemical pathways in crops involved in pathogen defense”woona.hr.)

  
  

• pH Buffering: Sheep’s wool tends to be naturally alkaline, which can influence soil pH. Raw wool has a high pH (around 8.5–9) due to residual compounds, meaning adding a lot of unprocessed wool can raise the soil pH slightlycompo.comcompo.com. This can be beneficial in acidic soils: wool acts like a mild liming agent, helping neutralize acidity. For example, a commercial wool pellet product (floraPell®) has a measured pH of about 8.8, and it was suggested as a remedy against over-acidification of soilwoona.hrwoona.hr. In acidic loam trials, wool pellets brought the pH up by a few tenths, creating a more favorable range for most crops (which prefer near-neutral pH). Moreover, wool’s ability to buffer pH swings is useful in container media – it can prevent soil from becoming too acidic as organic acids are produced during decomposition. However, in already alkaline soils (high pH), large amounts of raw wool could push pH higher, so caution is advised if growing acid-loving plantscompo.comcompo.com. Many wool pellet fertilizers today are blended with other organic materials to moderate this effect; for instance, products by some companies include added compost or meal to ensure the final fertilizer “no longer affects pH levels”, making it safe for all soilscompo.comcompo.com. In practice, wool pellets have a gentle liming effect – they can help raise pH on acidic sites, but will not drastically alter pH unless used in extreme excess. This pH buffering capacity means wool pellets can contribute to more stable soil pH over time, which helps nutrient availability. For example, phosphate availability often rises when very acidic soils are moderated; wool could indirectly improve P availability in such casesupdatepublishing.com. Overall, wool pellets tend to make soil conditions more neutral and favorable for a wide range of crops, except those that require strongly acidic conditions (e.g. blueberries may not enjoy wool unless it’s been treated to remove the high pH issue).

  
  

• Soil Nutrient Retention and Cation Exchange: Wool is about 50% carbon by weightmdpi.com and adds organic matter which improves cation exchange capacity (CEC) in soil. This is particularly useful in sandy, low-CEC soils that don’t hold nutrients well. By increasing organic matter, wool pellets help the soil retain cationic nutrients (like potassium, calcium, ammonium) and reduce leaching losses. In one study, adding wool to sandy loam significantly boosted the soil’s capacity to hold K and other nutrients, as evidenced by higher K levels measured in the soil after wool pellet applicationupdatepublishing.comupdatepublishing.com. The fibrous wool also physically traps nutrients that might otherwise wash away. Additionally, as wool decomposes, it slowly releases nitrogen in synch with plant uptake, which minimizes excess nitrates in the soil at any given timemdpi.commdpi.com. This slow-release behavior helps prevent nitrate leaching into groundwater (a common issue with fast-release fertilizers)mdpi.com. In clay soils, wool’s improvement of structure helps excess water (carrying dissolved nutrients) drain a bit faster, again reducing waterlogging and nutrient runoff. By enhancing overall soil health – moisture, structure, biology, and CEC – wool pellets contribute to soils that hold nutrients and water more efficiently, benefiting crops across the spectrum of soil types.

In summary, Table 2 highlights how wool pellet fertilizer addresses common challenges of different soil types:

Table 2. Soil Improvements from Wool Pellets in Various Soil Conditions

Soil Type	Benefits of Wool Pellets	Source
Sandy soils	Water retention greatly increased (fibers hold moisture, reducing drought stress); nutrient leaching reduced as wool boosts CEC and holds nutrients; soil structure improved by organic matter addition. In sand, wool pellets raised soil moisture by up to 25% during dry periodsupdatepublishing.com.	Correa et al. 2025updatepublishing.comupdatepublishing.com; Abdallah et al. 2019mdpi.commdpi.com
Clay soils	Aeration and drainage improved (swollen wool fibers create pore space, lowering bulk density by ~10%d-nb.info); reduced compaction as wool loosens the clay matrix; helps prevent waterlogging and root rot by absorbing excess waterfermesleystone.com. Overall stronger root growth in wool-amended clay due to better oxygen and structure.	Utah Farm Bureau (via UVM)mdpi.com; Ordiales et al. 2016woona.hrwoona.hr
Loamy soils	Balanced slow-release nutrition without nutrient imbalance (ideal for already fertile loams needing N boost but no P); maintains or slightly increases organic matter. Trials on loam showed wool pellets maintained soil organic matter levels throughout the season better than control (no decline)woona.hr. Provides steady N that complements loam’s moderate nutrient supply.	Ordiales et al. 2016woona.hrwoona.hr
Acidic soils	Raises pH modestly toward neutral (wool’s pH ~8.8 can counteract acidity)woona.hr; supplies calcium, magnesium and other base cations in trace amounts that help buffer aciditybioresourcesbioprocessing.springeropen.com. Thus, wool pellets can improve growth in acidic soils by reducing toxic aluminum availability and increasing nutrient availabilitycompo.comcompo.com.	Ordiales et al. 2016woona.hr; COMPO Ltd.compo.comcompo.com
Alkaline soils	Minimal additional P or salts: wool pellets contain virtually no phosphorus or soluble salts, so they won’t worsen high-P or saline conditions. (E.g., many western soils have excess P; wool adds N without Pmdpi.com.) Wool’s carbon can enhance microbial acid production over time, which may slightly mitigate high pH. However, high rates of raw wool could further raise pH, so pelletized products include amendments to neutralize thiscompo.com. In practice, moderate wool application is safe in alkaline soils and provides nutrients without aggravating alkalinity or salinity issues.	Bradshaw & Hagen 2022mdpi.commdpi.com; COMPO Ltd.compo.com

3. Nutritional Profile of Wool Pellets (Macro- and Micronutrients)

Wool pellets are a rich organic nutrient source, particularly valued for their high nitrogen content and complete array of minor nutrients. Table 3 provides a typical nutritional breakdown:

Table 3. Approximate Nutrient Content of Wool Pellet Fertilizer

Nutrient	Content in Wool Pellets	Notes
Nitrogen (N)	~9% (up to 10–12% in some products)mdpi.comwoona.hr; raw wool fiber contains ~15–17% N by weightbioresourcesbioprocessing.springeropen.com.	Primary nutrient in wool; mostly in protein (keratin). Slow-release form; fuels vegetative growth.
Phosphorus (P)	Negligible (~0–1%)mdpi.comkovonovak.com.	Wool alone is low in P; good for avoiding excess P buildup. May contain traces from dirt/soil on fleece.
Potassium (K)	~2–5%littleduckyflowerfarm.comcompo.com (some pellets 4–6% Kwoona.hr).	Significant K (from cellular salts in wool). Contributes to fruit quality and stress tolerance.
Sulfur (S)	~3–4% in raw woolbioresourcesbioprocessing.springeropen.com.	Wool’s keratin is high in sulfur amino acids. S is essential for protein synthesis and disease resistance (sulfur aids plant defense compounds).
Calcium (Ca)	Present (typical ~0.5–1% or more) in wool.	Derived from sheep sweat and environmental dust on wool. Helps soil structure and plant cell walls.
Magnesium (Mg)	Present (trace, often ~0.1–0.2%).	Wool provides a small amount of Mg, a central element of chlorophyll.
Micronutrients	Contains Iron (Fe), Zinc (Zn), Copper (Cu), Manganese (Mn), Sodium (Na), Boron (B), etc. in trace amountsbioresourcesbioprocessing.springeropen.com.	Wool accumulates minerals from an animal’s diet and environment. These micronutrients support various plant enzymes and processes.

Wool’s standout feature is its high nitrogen (N) content. Unwashed raw sheep’s wool typically contains about 10–12% nitrogen by weightcompo.com, which is far higher than most manures or composts (for comparison, compost might be 1–2% N). After processing into pellets, the guaranteed analysis of commercial wool fertilizers usually lists around 9-0-2 NPK (9% N, 0% P, 2% K)woollets.net. Some products show slight variations, such as 9-0-3 or 9-1-2, and one European wool pellet (floraPell) is reported at 10–12% N and 4–6% Kwoona.hr. The P content is consistently very low (often effectively 0% available P), which makes wool pellets unique as a nitrogen-heavy, phosphorus-free fertilizermdpi.com. This trait is environmentally beneficial in areas with P pollution concerns, as wool adds N and K without loading the soil with more phosphorusmdpi.comfermesleystone.com.

The nitrogen in wool pellets is organic (protein-based) and released slowly. Wool consists largely of keratin protein, which microbes must break down to release nitrogen. This process can take months – lab studies indicate wool’s N release can last up to a year or morecompo.com. Thus, wool pellets act as a slow-release N fertilizer, steadily feeding crops and minimizing leaching. For example, one trial noted that wool’s N was available throughout the growing season, with plants continuing to take up N from wool even late in the season, unlike quick-release fertilizer that might be gone from the root zone earlyprojects.sare.orgprojects.sare.org. The slow mineralization is temperature-dependent (faster in warm, moist soil; slower in cool conditions), which often aligns nutrient release with plant demand. This helps explain why wool-fertilized crops can achieve similar yields to those given fast-release fertilizers – the wool releases N at a rate that closely matches what plants can absorb, thereby improving nitrogen use efficiencyfermesleystone.comfermesleystone.com. In fact, a recent study concluded wool pellets are a “powerful alternative to inorganic fertilizers, offering a sustainable nutrient supply” due to this efficient N deliverystud.epsilon.slu.se.

Potassium (K) is the second notable macro-nutrient in wool. Potassium content around 4–5% is common in raw woolcompo.com. In practical terms, wool pellets provide a useful dose of K for plant health – K is vital for fruiting and osmotic regulation. A wool-fertilizer application that supplies ~100 kg N/ha would also add roughly 40–50 kg K/ha, which can support crop needs for potassium. In a lettuce study, soil K levels in wool-amended treatments were 10–53% higher than in control soil, demonstrating wool’s contribution of K to the systemupdatepublishing.comupdatepublishing.com. This K is released as the wool degrades and likely also comes from residual sweat (sheep sweat, called suint, contains potassium salts like potassium chloride). Notably, wool’s K is readily available since it’s mostly inorganic salts, so there is a portion of immediate-release K even while N comes out slowly. This gives plants an early boost in K nutrition.

Sulfur (S) is another significant element in wool. Sheep wool contains about 3–4% sulfur, mostly within the amino acid cystine in keratinbioresourcesbioprocessing.springeropen.com. As wool breaks down, it releases sulfate into the soil. Sulfur is increasingly recognized as an important “secondary” nutrient for crops (needed for protein synthesis and as a component of certain vitamins and defense compounds). Wool’s high sulfur content can help prevent S deficiencies in crops. In fact, sulfur in wool may improve nitrogen utilization by plants – sulfur is required to make use of nitrogen in protein formation. Adequate S from wool could thus synergistically enhance the fertilizer value of the wool’s N. Additionally, there is a link between sulfur nutrition and plant disease resistance: S is needed to produce certain antifungal/antibacterial compounds in plants. By supplying slow-release sulfur, wool fertilizer might bolster plants’ inherent disease resistance (sulfur-deficient plants are known to be more susceptible to some diseases)etsy.com. This could partly explain anecdotal reports that wool-fed plants have stronger pest and disease tolerancebackyardboss.net. While not a fungicide per se, wool pellets indirectly contribute sulfur nutrition in a way that keeps plants healthy.

Wool pellets also contain calcium, magnesium, and micronutrients in small quantities. Sheep wool can pick up minerals from soil, feed, and dust. For example, analysis of wool ash finds calcium present, which corresponds to wool pellet fertilizers having some Ca (useful for crops to build cell walls and for mitigating soil acidity). The magnesium content, though modest, is beneficial for chlorophyll and enzyme function. Micronutrients like iron, zinc, copper, and manganese are all detected in wool (often in the ppm range). Over time, as wool fully decomposes, these micronutrients become part of the soil pool and available to plants. This makes wool pellets more akin to a complete organic fertilizer – they don’t just supply NPK, but a broad spectrum of nutrients. For instance, an analysis noted that keratinous wool releases not only N (~16% of its mass) and S (~3%), but also measurable amounts of Ca, Na, K, P, Mg, Zn, Fe, Cu, and Mnbioresourcesbioprocessing.springeropen.com. Although each of these is in trace amounts, their presence can help prevent micronutrient deficiencies, especially in organic systems where synthetic micronutrient fertilizers aren’t used. Farmers using wool pellets have reported improvements in plant color and vigor that might be partly due to these micronutrients (e.g. greener leaves from iron and magnesium, better flowering from zinc and boron, etc.).

It’s important to note that the nutrient content of wool pellets can vary slightly depending on wool source and processing. “Grease wool” (unwashed wool straight from the sheep) will have higher potassium and perhaps slightly lower nitrogen availability initially (due to the lanolin content). Scoured (washed) wool will have a higher proportion of pure keratin (hence higher N percentage by weight) but less K (since washing removes the soluble salts). Some wool pellet manufacturers mix wool with other organic materials (e.g. compost, manure, feather meal) to balance the NPK ratio – for example, one product boasts an NPK of 9-1-2, indicating a small phosphorus addition in the manufacturing processkovonovak.com. Another product lists 11-0-5, presumably a wool blend with higher Kagainfarmstead.comagainfarmstead.com. Generally, though, 100% wool pellets hover around 9–10% N, ~0.1% P, and 2–5% K, plus the secondary and micronutrients as discussedmdpi.comwoollets.net.

From an agronomic perspective, this nutrient profile means wool pellets function primarily as a nitrogen fertilizer (like blood meal or feather meal), with the bonus of some potassium and sulfur. Crops that require a lot of N (leafy vegetables, corn, brassicas, etc.) respond especially well to wool fertilizer. At recommended application rates (often ~5% of soil volume in potting mix, or a few hundred grams per square meter in field application), wool pellets can deliver a season’s worth of N. Yet because of the slow release, there’s little risk of burning plants with excess nitrogen – seedlings and salt-sensitive plants handle wool fertilizer well. The lack of phosphorus in wool is advantageous when fertilizing already P-rich soils (common in areas with long manure histories); wool won’t exacerbate P runoff issues. Growers in Vermont specifically sought wool pellets for this reason – their soils had ample P, so they needed a P-free nitrogen sourcemdpi.comfermesleystone.com. Wool pellets filled that niche by providing N (and some K) without P, thus allowing crops to utilize existing soil P while avoiding new P inputsfermesleystone.comfermesleystone.com. This helps reduce the risk of phosphorus leaching into waterways (a cause of algal blooms).

Finally, the nutrients in wool are all organic and derived from a renewable resource (sheep fleece), making wool pellets compliant with organic farming standards. There are no synthetic chemicals – the pellets are simply wool mechanically compressed. As they break down, they leave no harmful residues; in fact, after full decomposition (which can take 1–2 years), the wool is gone and what remains is humus and stabilized organic matter that continues to benefit soil structureextension.sdstate.eduwoona.hr. This natural composition means wool pellets not only feed the current crop but also contribute to the long-term fertility of the soil.

4. Other Agronomic and Environmental Benefits

In addition to the crop growth and soil health benefits already described, wool pellet fertilizers offer several other agronomic and environmental advantages:

• Slow-Release, Long-Lasting Fertility: Wool pellets provide a sustained nutrient release, functioning as a long-term fertilizer. Unlike quick-release chemical fertilizers that can dump nutrients rapidly (with much lost to leaching or volatilization), wool’s nutrients trickle out as microbes degrade the fibers. This gives a “fertilizer effect” that can last for months and even into the next growing seasoncompo.comwoona.hr. Some studies note that a single application of wool pellets can feed a crop for an entire season (5+ months)compo.com. In one trial, only one application in spring was needed for the whole growing period of vegetablescompo.com. Wool’s slow release aligns well with plant growth curves, reducing the need for repeated fertilizer applications. This not only saves labor but also prevents the “feast or famine” cycles of nutrition that can stress plants. Moreover, any portion of the wool not fully decomposed by season’s end continues to break down the following year, so there’s a residual fertilizer effect. Gardeners have observed that wool pieces remaining in soil over winter still release nutrients for the next planting, essentially biodegrading over 1–2 years and enriching two seasons of cropsextension.sdstate.edu. This longevity improves nutrient use efficiency – more of the applied nutrient ends up taken by plants rather than lost. It also means wool pellets can be applied at higher rates without fear of burning plants, since the nutrients are locked in organic form and only gradually become plant-available.

  
  

• Biodegradability and Soil Organic Matter: Wool pellets are completely natural and biodegradable. Within a year or two, soil organisms will have transformed the wool into humus, CO₂, water, and mineral nutrients. There is no accumulation of any synthetic material (unlike some slow-release fertilizers that leave coatings or plastic residues). The carbon from wool (about 50% of its weight) becomes part of soil organic carbon, contributing to carbon sequestration in the soilmdpi.com. Using wool as fertilizer thus has a climate benefit: it takes a waste product (sheep wool often considered low-value or landfill-bound) and locks a portion of its carbon into the soil as stable organic matter. Farmers looking to improve soil organic matter will find that wool pellets, besides fertilizing, add organic carbon and help build long-term soil fertility. For example, in the processing tomato trial, plots fertilized with wool pellets maintained their soil organic matter level through harvest, whereas control plots saw a slight declinewoona.hr. This indicates wool helped offset decomposition losses by contributing new organic material. Over multiple years, using wool pellets could gradually increase soil organic matter, leading to better soil structure, moisture holding, and cation exchange capacity. Environmentally, the biodegradability means there’s no pollution or disposal issue – the wool simply becomes part of the soil ecosystem. This contrasts with some conventional fertilizers that can leave behind salts or acidify the soil. Wool’s breakdown tends to mildly alkalize and enrich the soil, essentially acting like a slow compost. From a sustainability viewpoint, wool pellets close a resource loop (waste wool → soil input) and reduce reliance on mined fertilizers.

• Reduced Nutrient Leaching and Runoff: As mentioned, the controlled release nature of wool pellets markedly reduces nutrient leaching. Nitrogen from wool is released primarily via microbial activity, so it doesn’t all convert to soluble nitrate at once. Studies have emphasized that wool’s slow N release “helps avoid the risk of nitrate leaching and runoff before plants can utilize the nutrient”mdpi.com. This is a critical environmental advantage, as nitrate pollution of groundwater is a serious concern in many agricultural areas. By the time wool’s nitrogen is mineralized to nitrate, plant roots are usually actively growing and ready to absorb it, thus keeping it out of waterways. In addition, since wool pellets contain almost no phosphorus, they inherently prevent phosphorus runoff problems – a big benefit for regions where P runoff causes algae blooms. Researchers at University of Vermont highlighted that wool pellets enable crops to tap into existing soil P, and by not adding more P, they mitigate the risk of excess P washing into nearby water bodiesfermesleystone.comfermesleystone.com. Using wool fertilizer is therefore a water quality-friendly practice. It aligns with nutrient management goals to supply needed N without the collateral damage of P pollution. Wool pellets also lack the high soluble salt content of many chemical fertilizers, meaning less risk of salt runoff or accumulation. Overall, wool fertilization is gentle on the environment: nutrients are delivered in the soil-plant system with minimal losses to the air (ammonia volatilization is low because the N is bound in organic form) or water.

• Weed Suppression (Physical Mulch Effect): An interesting side benefit observed when wool pellets or raw wool are applied to the soil surface is weed suppression. Wool fibers can form a dense mat when spread on top of soil (as mulch) or even when mixed in, the swelling pellets can create a less hospitable environment for weed seeds. Garden trials and anecdotal evidence report that a layer of wool pellets on the soil inhibits weed germination – the fine wool fibers entangle and block light to weed seeds, much like a mulchextension.sdstate.edu. One extension source notes that using raw wool as a mulch “makes it difficult for weeds to penetrate”extension.sdstate.edu. With pellets, if they are top-dressed and then watered, they expand and form a woolly barrier that can deter weed emergence around plants. This can reduce the need for herbicides or laborious weeding. It’s not 100% weed-proof, but any emerging weeds are often weak and sparse. Additionally, slugs and snails are deterred by wool mulch/pellets – gardeners have found fewer slugs in beds mulched with wool, likely because the wool’s texture (especially when dry) is irritating to the soft-bodied slugsextension.sdstate.eduextension.sdstate.edu. The fibers can act like tiny bristles that pests avoid crawling over. This is an organic pest control bonus of wool amendments, potentially protecting tender plants from slug damage without chemicals. (Some commercial wool pellet products even advertise themselves as natural slug repellents.) While wool pellets are primarily used mixed into soil, these side effects when used near the soil surface are valued by growers looking to suppress weeds and pests naturally.

• Temperature Moderation: Wool is well-known as an insulator (it keeps sheep warm!), and this property carries over to the soil environment. When used as a mulch or when a significant amount is in the topsoil, wool can help buffer soil temperature fluctuations. It slows the heating of soil under intense sun and reduces heat loss on cool nights. In spring, wool mulch can protect plant roots from late frosts by providing an insulating layerwildvalleyfarms.com. Conversely, in hot climates, wool in soil may keep the root zone slightly cooler and moister by shading and retaining water. This temperature regulation can reduce stress on plants and create a more favorable microclimate for root growthwildvalleyfarms.com. For example, growers have noted that wool-insulated soil experiences less crusting and extreme drying on the surface, which helps seedlings establish. While this is more pronounced with wool felt mats or thick wool mulch, even pellets mixed in soil add some thermal mass and insulation due to trapped air in fibers. This can extend growing seasons or improve seedling survival in marginal conditions.

• Integration into Circular Farming Systems: Using wool pellets ties animal agriculture to crop production in a sustainable loop. It provides a use for low-grade or waste wool from sheep farmers, turning what was once a disposal problem into a valuable input on farmsprojects.sare.org. In regions like New England, coarse wool has little market value for textiles, so repurposing it as fertilizer gives sheep farmers an additional income stream and incentive to manage wool responsibly. Meanwhile, vegetable and crop farmers gain a local, renewable fertilizer source, reducing reliance on mined or synthetic fertilizers. This plant-animal integration enhances overall farm sustainabilityprojects.sare.org. There is also an energy benefit: wool pellets are produced with relatively low energy (simply cleaning and pressing wool), unlike synthetic N fertilizers which are energy-intensive to manufacture. Thus, the carbon footprint of wool fertilizer is low, especially if used locally. By embracing wool pellets, farming systems can become more circular – nutrients cycle from sheep feed, to wool, to soil, to crops, and back to feed or humans, with minimal wastage. This is seen as a model for agroecological farming, closing nutrient loops and reducing external inputsprojects.sare.orgfermesleystone.com.

• Safe and User-Friendly: From a farmer/gardener perspective, wool pellets are safe to handle and use. They are not caustic or odorous (a mild “sheep” smell may be present initially but is generally not unpleasant). They do not pose pathogen risks like some manures or biofertilizers – wool has been tested and found free of common livestock diseases or fecal bacteria since it’s just wool fiber (any pathogens that might have been in fleece wash out or are rendered inactive during pelletizing and soil incorporation)mdpi.com. For instance, a project producing organic sheep wool pellets confirmed that the product has no detectable disease agents (like scrapie prions or E. coli) due to the heat and pressure of pellet formationmdpi.com. Wool pellets are also easy to apply: the pellets are lightweight, dry, and flowable. They can be scattered by hand or with a spreader, or simply mixed into potting soil. Once watered, they begin their work by swelling and releasing nutrients. Their light weight reduces transportation energy and makes them convenient for rooftop gardens or planters where heavy soil amendments are impractical. All these factors make wool pellets an accessible fertilizer option for small-scale gardeners up to large-scale farmers.

In conclusion, wool pellet fertilizer offers a compelling suite of benefits: it effectively nourishes a wide variety of crops, improves soil water and nutrient retention across soil types, provides key nutrients (especially nitrogen) in a slow-release, plant-friendly form, and contributes to sustainable farming by recycling a natural fiber. The evidence from scientific studies and field trials shows that wool pellets can increase crop yields (often matching conventional fertilizers), enhance root development (through better soil structure and aeration), and possibly improve plant resilience (via sulfur nutrition and steady growth). All of this is achieved while also protecting the environment – reducing nutrient leaching, avoiding phosphorus pollution, and building healthier soils. As research continues (including ongoing studies on large-scale crop production with wool pelletsmontana.edu), it is increasingly clear that this once-discarded sheep byproduct can play a valuable role in modern sustainable agriculture.

Sources:

1. Bradshaw, T. & Hagen, K. (2022). Wool Pellets Are a Viable Alternative to Commercial Fertilizer for Organic Vegetable Production. Agronomy, 12(5):1210. (University of Vermont study on tomato and spinach yields with wool vs. organic fertilizer)projects.sare.orgprojects.sare.org

2. Correa, L. M., et al. (2025). Effect of wool pellets on soil fertility and lettuce growth in three soil types. J. of Aridland Agriculture, 11: 21–29. (Chile study showing improved moisture retention and lettuce yield in sand, clay, peat with wool)updatepublishing.comupdatepublishing.com

3. Ordiales, E., et al. (2016). Assessment of Utilization of Sheep Wool Pellets as Organic Fertilizer and Soil Amendment in Processing Tomato and Broccoli. Mod. Agric. Sci. Technol., 2(2):20–35. (Field trials in Spain: wool pellet fertilizer at 2000 kg/ha maximized tomato & broccoli yields)woona.hrwoona.hr

4. Abdallah, A. M., et al. (2019). Assessment of two sheep wool residues from textile industry as organic fertilizer in sunflower and maize cultivation. J. Soil Sci. Plant Nutr., 19:793–807. (Pot experiments: wool (carbonized vs raw) enhanced sunflower and maize growth; wool met maize N needs)link.springer.comlink.springer.com

5. Vončina, A. & Mihelič, R. (2013). Sheep wool and leather waste as fertilizers in organic production of asparagus. Acta Agric. Slov., 101(2):191–200. (Reported positive use of wool waste in asparagus)mdpi.com

6. Suruchi, G., et al. (2014). Growth, macro and micronutrient concentration in clusterbean (Cyamopsis tetragonoloba) plant tissue as well as in soil when amended with wool as fertilizer. J. Environ. Res. Dev., 8(3):607–613. (Found wool fertilizer increased nutrient levels in soil and cluster bean plants)mdpi.com

7. Zheljazkov, V. D., et al. (2009). Wool-waste as organic nutrient source for container-grown plants. Waste Management, 29:2160–2164. (Demonstrated wool waste improved growth in potted herbs and ornamentals)mdpi.combioresourcesbioprocessing.springeropen.com

8. COMPO Gardening Guide (2021). Sheep’s wool as fertilizer? (Explains properties of raw wool and wool pellets; nutrient content ~12% N, 5% K; slow release and water-retention benefits)compo.comcompo.com

9. SDSU Extension (2024). Wool: A Natural Bio-Enhancement for Gardens. (Extension article summarizing wool pellet benefits: ~9% N, equal or greater yields vs. fertilizer, 20–30x water holding, weed suppression, 2-year decomposition)extension.sdstate.eduextension.sdstate.edu

10. Leystone Farms (2024). Wool Pellet Research Results. (Farm summary of UVM research: wool pellets reduce P runoff, enhance nutrient use, increase tomato and spinach yields, improve moisture management)fermesleystone.comfermesleystone.com