OVERVIEW OF EARTHWORM CASTS AND A COMPARISON WITH COMPOST

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OVERVIEW OF EARTHWORM CASTS AND A COMPARISON WITH COMPOST

WASTE PROCESSING BY EARTHWORMS

Optimal conditions for earthworm activity

Cool temperature: between 0 and 35oC

Not too much water (85% moisture)

Mineralization in the earthworm gut

As feed passes through the earthworm gut the material is mineralized and plantnutrients are available. The grinding effect of the gizzard and the passagethrough the gut leads to the formation of a granule

(15) (16).

Casts have a structure that is similar to a slow release granule: it has an organicmatter core and a clay casing

(1).

Casts benefit to plants

Casts contain the necessary nutrients for plant growth: when added in sufficient

amounts, as in 4-10 Kg casts / m2, casts can out-yield NPK fertilizers (100 Kg

N / m2)

(13).

Casts increase plant dry weight and N, P, Mg and K uptake from the soil (12)

.

The presence of earthworms increases plant growth and N uptake as opposed to

unfertilized soil (19).

Casts have a hormone-like effect that increases germination and growth rate(14)

.

Waste preparation for processing by earthworms



Organic debris are more palatable to earthworms if it’s fresh or incubated for up

to 2 weeks. The particle size of organic matter doesn’t matter(23)

.

Earthworms have less requirements than microbes in processing carbon andnitrogen

(24). The C:N ratio which results in the most stable earthworm casts is

25 (Ndegwa and Thompson, 2000).

High salinity levels and alkalinity harm earthworms. Earthworms are also

sensitive to pesticides(25)

.

Types of earthworms used

Earthworms are chosen for their resistance to extreme conditions and feedingand reproductive rate. They also need to survive handling.

Eisenia foetida is the most efficient in waste processing, while Eudriluseugeniae is large, fast growing, reasonably prolific and would be ideal for protein production Eudrilus eugenia

(17).

CASTS OR COMPOST?

Both are organic products which provide the plant with nutrients, good soil aeration and

other un-identified advantages (the “organic matter effect”)(10)

.

Comparison as to plant nutrients

Plants treated with compost may still show N deficiency, even when syntheticfertilizer is added. His is due to N immobilization: microorganisms in compost

use N for their metabolism (3).

More decomposition (Lignolysis) occurs and higher levels of Nitrogen arereached when waste is fed to worms than in composting. Casts also increase

protein synthesis in plants(7)

.



Compost can be an incomplete fertilizer, most plants have a an increase in yield

with the addition of compost, organic N sources can cause a short term yield

decrease(18)

.

Comparison as to the timing of nutrient release

Slow nutrient release is more synchronized with plant needs, and leads tohigher yields

(9).

Casts have a structure that is similar to a slow release granule: it has an organicmatter core and a clay casing

(1).

In my master’s thesis (Chaoui et al, 2003) I showed that casts show a slowernutrient release rate than compost, possibly explaining the higher plant weight

to nutrient content ratio.

Comparison as to salinity level

Ammonium is the main contributor to salinity levels.

High salinity levels cause osmotic drought.

NH4 levels are high in fresh casts but casts stabilize after 2 weeks of aging

through nitrification. The acidity level in casts is slightly low, which reducesdenitrification

(5). Salinity levels are moderate in casts, since passage through

the earthworm gut does not increase the level of some salts (Ca, Mg, Na) (2)

.

Some composts have high concentrations of ammonium or soluble salts (6)

.There are larger amounts of NH4 than NO3 in composted domestic waste. High

Levels of NH4 are due to non-stabilized substances(4)

. Immature (unfinished)compost can stunt or kill plants, and reduce germination and growth

(11).

Comparison as to pathogens

Recycling organic waste through earthworms also results in a product with a

lower pathogen level than compost (8)

.

Since high temperature are not part of the earthworm cast production process

disease suppressing microorganisms that may be present in this material

survives in the absence of heat(20)

.



Some composts are suppressive of plant pathogens but heating them to 60oC for

five days reduced suppressiveness. This is why some composts need to be

inoculated with disease suppressing microorganisms. Adding nutrients (i.e.reducing competition) also reduces disease suppression by composts

(21).

Comparing Earthworm Casts and Compost as to their processes

Comparison as to time and volume requirement

Earthworms eat 75% of their weight daily (Ndegwa, 1999) and the speed or

earthworm casts production can be increased by increasing the amount ofearthworms. The layer of waste needs to be 1 ft or thinner to prevent anaerobic

conditions which hinder earthworm activity.

A compost pile needs to be 3 cubed feet to hold heat in winter and takes 3-4months to be cured

(22).

Comparison as to odor problem

Odorous gases are emitted as compost piles heat up. Specific layering ofcomposting material needs to be used to prevent odor.

Earthworms don’t require heat to process waste (heat is actually detrimental).In the correct waste to worms ratio fermentation and heat can be prevented, and

also odor or flies.

Aeration requirements

Compost needs aeration (and labor) to maintain aerobic conditions for microbial

activity.

Worms dig canals (burrows) as they process waste which indirectly aerates the

processed material.



(1) Casts have a structure that is similarto a slow release

granule: it has an

organic matter core anda clay casing.

Casts Structure

In Chan & Heenan (1995) worm casts had a composite structure, made of units 210-

500 micro-m in diameter which were made of smaller spherical subunits (50-100micro-m). Casts were significantly more water stable and higher in total nitrogen

than in soil aggregates of the same size. Porosity in the casts was created by spaces

between the subunits, which were composed of very densely packed clay/silt size

particles. Evidence from scanning electron microscopy suggests the high stabilityto be due to the presence of cements (Chan & Heenan, 1995). In Fragoso et al.

(1993) casts structure of the Trigaster earthworm species showed granules

composed of organic debris fractions (250-2000 m). When earthworms were

added to soil made of 1-2 mm aggregates (Schrader et al . 1994), molding processesin the earthworm gut destabilized the soil structure but at the same time biochemical

processes act as an antagonistic stabilizing system. Shipitalo (1986) observed that

freshly deposited moist casts were 26 to 41% more dispersible than uningestedmoist soil due to disruption of some existing bonds during gut transit. When casts

were aged or dried there was a stronger bond of plant microbial polysaccharides and

other organic materials to clay, predominantly via clay-polyvalent catio-organic

matter (C-P-OM) linkages involving calcium (Shipitalo, 1986). Zhang & Schrader(1993) showed that organic C and CaCO3 act as bonding agents and the CaCO3 is

involved with binding linkages with organic matter during digestion, the more

stable are the formed aggregates. They also observed that in L. terrestris casts were

very water stable, maybe due to the presence of Ca humate or organic matter- polyvalent cation-soil particle bonds. Organic C in those same casts increased by

21 to 43%. Water extractable polysaccharides increased too, maybe due to

enrichment of mucopolysaccharides during ingestion, or from cutaneous polysaccharides (Zhang & Schrader, 1993). In Marinissen & Dexter (1990) aging

made casts more stable, probably due to fungi that developed on the surface of 6

days old casts. Artificial casts were made by molding soil at 100% moisture and pushing it through a 1.5 mm opening syringe, and compared to natural casts as to

stability, which was measured as the capacity to prevent clay dispersion. Internal

stability was measure by breaking down casts (magnetic stirrer) and the external one

by using a paddle stirrer. Stability of the aggregate surface increased with aging but

was the internal stability remained the same. Since internal stability seems todepend on % of microaggregates, no new ones were formed (Marinissen & Dexter,

1990). Shipitalo & Protz (1989) observed that earthworms fragmented litter bygrazing and a liquefied soil and debris mixture formed in their gut. In the gizzard,

more fragmentation, microbial activity and digestive enzymes decompose organic

matter, which becomes part of the soil plasma. Lignified particles resistfragmentation and clay minerals are brought close to newly formed bonding agents

(polysaccharides). The organic matter enriched plasma adheres to surfaces of the



organic skeleton of resistant organic fragments (with the help of bonding material),

forming new aggregates. Pellets are excreted in this state and both drying and agingstrengthens the bond between organic and mineral components. Therefore Shipitalo

& Protz (1989) concluded that ingestion of soil and litter in earthworms brings clay

in close contact with decomposing organic fragments, creating the organic matter

cored microaggregates. Organic matter is therefore encapsulated by clay and itresists rapid decomposition. The linkages within the aggregates consist of clay-

polyvalent cation - organic matter (C-P-OM) bonds and they seem to makeaggregates more stable.

(2) Salinity levels are

moderate in casts, since

passage through theearthworm gut does not

increase the level of

some salts (Ca, Mg, Na).

Salinity in Earthworm Casts

Casts seems to reduce the salinity problem caused by an excess of NH 4 in an

experiment where tomato plants were grown in sand, clayey loam, and garden

soil processed by Californian earthworms. Feeding with NH4 (instead of NO3)

slowed down plant growth in sand, less in loam, and not at all in soil processed by earthworms (Borowski, 1995). Basker et al. (1993) observed that

exchangeable Ca, Mg and Na were marginally higher in casts than in non-ingested soil, soil, and that ingestion by earthworms increased he potassium levelof the soil.

(19) presence of worms

increases plant growth

and N uptake asopposed to unfertilized

soil.

Effect of Casts on Plant Growth

In the 1980’s, at a research station in Rothamsted, earthworms were collectedand put in buckets of clean water, in batches of 250. A solution of 0.2%

formaldehyde was spread on the field to drive the worms out of their burrows.

They were then rinsed in a second bucket of clean water and spread at a rate of

250 worms m

-2

over a landfill site capped with 15cm of clay subsoil, treated withdomestic dried sewage solid at 10 tons ha-1

and planted with grass. A higher

plant growth was observed in the presence of worms (Edwards & Bates, 1992).

According to Haimi (1992) birch seedlings planted in soil with earthworms had33% and 24% more leaf and stem biomass respectively than in those grown in

pots without earthworms. Root biomass was slightly lower in the earthworms

than in the bare soil treatment and N content of leaves was twice higher in thetreatment with earthworms. This was only partially explained by earthworm

mortality. N uptake increases in the presence of earthworms and is correlated (r

= 0.85) with the increase in CO2 production (Ruz – Jerez, 1992).

(3) Plants treated with

compost may still show N deficiency, even when synthetic fertilizer is

added. His is due to N

immobilization:

microorganisms incompost use N for their

metabolism.

Nutrient Dynamics in Compost

Cocomposted sewage sludge is obtained by aerobic digestion of municipal refuse

and anaerobically digested sewage sludge. N immobilization can be a problem in

these composts. Plants showed N deficiency symptoms even when supplied with

NH4 NO3, along with reduced dry matter production and lower plant Nconcentrations. Also there was no difference between the 11, 22 and 44 tons of

compost ha-1

. Therefore when applied at agronomic rates compost can support

plant growth, id adequate amounts of supplemental N fertilizers are used (Sims,



1990).

(4) There are larger

amounts of NH 4 than

NO3 in composteddomestic waste. High

Levels of NH 4 are due tonon-stabilized substances.

Nutrient Dynamics in Compost

Composted urban refuses were studied as organic fertilizers (Villar et al., 1993).

Most of the total N was in organic forms; NH4 was more abundant than NO3, and

calcium was the most abundant nutrient followed by K, Na, Mg and P. Most ofthe Ca and Na were in available forms; available K and Mg were lower and

available P very small. Although compost was unbalanced with regard to the

main nutrients, it had potential agronomic value. Total C contents and C/N ratiosin the three non-amended composts were in the range for stabilized composts;

however, the NH4 content seemed to point to the presence of non-stabilized

substances (Villar et al., 1993).

(5) NH 4 levels are high

in fresh casts but casts

stabilize after 2 weeks ofaging through

nitrification. The aciditylevel in casts is slightly

low, which reducesdenitrification.

Nutrient Dynamics in Earthworm Casts

In fresh casts, NH4 levels were very high (294.2-233.98 g g-1

dry cast) duemineralization in the earthworm gut. During the first week of cast aging, NH4

levels decreased while NH3 levels increased, due to rapid nitrification in the freshcasts. After two weeks the levels of NH4 and NO3 were stabilized, probably dueto organic matter protection in dry casts (Decaens, 1999). Casts tend to stabilize

through nitrification after being deposited; in a garden soil processed by

earthworm ammonium underwent complete nitrification compared with 33 and

9% nitrification in loam and sand, respectively (Borowski, 1995). In Decaens(1999) C increased during cast aging (+100%), possibly because of CO2 fixation

or macrofaunal activities in casts. Stabilized earthworm casts leached less

dissolvable organic carbon than from undigested soil. Nutrient losses from caststhat underwent several wetting / drying cycles show that there was a strong

protection of nutrients in casts at first, but this was reduced as the aggregate

structure was weakened (McInerney et al., 2000). After a 20 days longincubation of fresh casts a rapid increase in mineral N was observed during thefirst few days after deposition, and then a decrease to a level 4.5 times higher

than in the soil. Also the NH4 level was higher in fresh casts than in the control

(Rangel, 1999). The decrease of mineral N in time in casts can be due to N becoming microbial biomass, volatilized, denitrified, or leached (Lavelle, 1992).

In Haynes (1999) uningested soil and casts were incubated for 42 days, and

extractable P levels were similar in casts and soils during the initial stages ofincubation, but were larger in casts after 28 and 42 days. Activities of

arylsulphatase and acid phosphatase were lower in casts than in uningested soil,

therefore the mineralization of organic matter during gut transit could be the

reason for the increase in extractable P and S during incubation. Haynes (1999)concluded that mineral N increases because of mineralization in the gut, but P

and S levels increase due to mineralization after egestion. In Lavelle (1992)

mineral N in casts was mostly in the form of ammonium, and after a 26 days long

incubation NH4 was nitrified or immobilized in biomass. The incubation of soil before ingestion increased NH4 production in casts and being slightly acidic casts

do not favor the denitrification of NO3. Biomass N was stable (relatively) after

an initial flush on day 1. Processing by earthworms increases lignin



mineralization, as compared with just mixing with soil and the passage in the gut

might affect lignin structure (Scheu, 1993).

(6) Some composts have

high concentrations ofammonium or soluble

salts.

Salinity in Compost

The salinity problem is shown in O'Brien & Barker (1996) by the inhibitions in

seed germination and in plant growth in some composts, which is associated withhigh concentrations of ammonium or soluble salts in the media. Ammonium-N

in the compost declined with time (over 28 days), whereas nitrate-N and

electrical conductivity initially increased then decreased with time. Ammoniumsalts appear to be lost from the compost more rapidly than nitrate salts, which

have a prolonged inhibitory effect on germination and growth (O'Brien & Barker,

1996).

(18) Compost can be an

incomplete fertilizer,

most plants have a anincrease in yield with

the addition of compost,organic N sources can

cause a short term yielddecrease.

Effect of Compost on Plant Growth

An increase in soil productivity, which cannot be explained by mineral

nutrients alone, is often recorded when composted organic wastes are supplied to

croplands. This is the so-called "organic matter effect" suggests that mechanismsother than simple nutrient supply can contribute to plant growth (Galli et al.1992). Hountin et al. (1995) studied the effect of peat moss-shrimp wastes

compost on barley (Hordeum vulgare L.) applied alone or with NPK, and he

concluded that the main effect of compost on straw yield, numbers of tillers, plant height, and number of ears was more important than that of fertilizer.

Compost was considered incomplete as a fertilizer in Hartz et al. (1996) when

composted green yard and landscape waste and peat were evaluated as to plantnutrient supply. Both were mixed with perlite and added to pots planted with

tomatoes and marigolds at a volume ratio of 1:1. Fertigation regimes of 0, 50, or

100 mg L-1

of 15N-13P-12K). Compost was equivalent or superior to peat in

plant growth and it contributed to crop macronutrient nutrition, but the highestfertigation rate was required for optimum growth. In Chong et al. (1991)

deciduous ornamental shrubs were grown in 33%, 67%, and 100% of three

different sources of compost. Despite large variation in species growth responseto sources and levels of compost, most grew equally well or better in the

compost-amended regimes than in the control and were influenced little, or not at

all, by initial or prevailing salt levels in the media. Shoot and root dry weight of

some plants increased with increasing compost levels. The reverse relationshipoccurred (all sources) in shoot and root dry weight of privet and root dry weight

of weigela and potentilla. Leaf nutrients (N, P, K, Ca, Mg, Fe, Mn, and Zn)tended to increase with increasing compost levels, but not all species showed this

response with all nutrients. Regardless of compost source or level, all shrubswere of marketable quality when harvested, except privet, which showed leaf

chlorosis in all compost-amended regimes (Chong et al., 1991). Fauci & Dick

(1994) observed that the efficiency of organic N uptake from organic fertilizersvaries with the type of fertilizer, and organic N sources can cause short-term crop

yield decreases. 10-30% of N was taken up when poultry manure or pea vine

residues were added (Fauci & Dick, 1994).



(10) Both are organic

products which providethe plant with nutrients,

good soil aeration and

other un-identified

advantages (the“organic matter effect”)

(effect of compost on plant growth)

An increase in soil productivity, which cannot be explained by mineral nutrients

alone, is often recorded when composted organic wastes are supplied tocroplands. This is the so-called "organic matter effect" suggests that mechanisms

other than simple nutrient supply can contribute to plant growth (Galli et al.1992).

(7) More decomposition(Lignolysis) occurs and

higher levels of Nitrogen

are reached when waste

is fed to worms than incomposting. Casts also

increase protein

synthesis in plants.

Compost as Compared to Casts

In Vinceslas-Akpa & Loquet (1997) lignocellulosic wastes (of maple) werecomposted and vermicomposted (i.e. ingested by earthworms) for 10 months

under controlled conditions. At first, total organic matter and carbon decreased

rapidly, while cellulose was decomposing. Aromatic structures and lignin began

to decompose after one month of composting. More ligninolysis occurred in the

vermicompost. The C-to-N ratio decreased, showing changes in total C andhigher levels of N in the vermicompost. The two materials evolved differently:

casts had a lower aromaticity ratio, and a higher protein-to-organic matter ratiothan in compost, which indicates a higher level of humification (Vinceslas-Akpa& Loquet, 1997). When casts and compost were compared in a pot experiment

casts increased protein synthesis in lettuce seedlings by approximately 30%,

whereas no differences were recorded in the presence of compost (Galli et al.1992)

(8) recycling organic

waste through

earthworms also results

in a product with alower pathogen level

than compost.

Compost as Compared to Casts (continued)

The process of vermicomposting can also result in a product with a lower

pathogen level than compost (Eastman, 1999).

(9) Slow nutrient release

is more synchronized

with plant needs, andleads to higher yields.

Effect of Nutrient Availability and slow release on Plant Growth

When supplied with inorganic nitrogen, grain sorghum plants were found to havea higher intake rate than when supplied with organic nitrogen (Jordan, 1996).

Al-Karaki (1995) exposed plants to P stress and found that lower dry matter in

shoot and root was due to less water uptake, and not to P deficiency. Catanazaro(1998) showed the importance of the synchronization between nutrient release

and plant uptake by comparing alternate liquid fertilization, constant liquid

fertilization, resin coated slow release fertilizer and slow release fertilizer tablets.When he provoked leaching less nutrients leached with the slow release products.In the same study slow release tablets caused nutrient deficiency and slow release

resin coated fertilizer had the most efficient N uptake 64-68% as compared to 41-

46% in liquid fertilizer. Several methods were tested by Choi & Nelson (1996)in order to obtain a slow release fertilizer, which would be more synchronized

with the nutrient requirement of the fertilized plant: to prolong the period of N a

bacterium - Brevibacterium lactofermentum - was bonded to kraft lignin, a



substance highly resistant to degradation. To retard mineralization further, the

bacterium-lignin mixture was reacted with formaldehyde to form amino cross-links within and between protein chains. Bonding to lignin was undesirable

because N release occurred during the same period as from the bacteria unbound

to lignin and the total amount of N recovered was reduced to only 42%. Cross-

linking with formaldehyde was less desirable since N was released mainly duringthe first 4 weeks and the total amount of N released was even lower than for the

bacterium-lignin mixture. Additions of urea to the latter reaction did not improvesubsequent N mineralization. In a second set of treatments lignin was withheld

and the bacterium was reacted with formaldehyde. Five percent formaldehyde by

weight (of the bacterium) successfully reduced release of N during the first 4

weeks and increased it thereafter. In this treatment N was released from week 2through the end of the test (12 weeks). Peak release occurred at 6 weeks. This

resulting N source could be combined with other slow-release N sources to form

a slow release N fertilizer (Choi & Nelson, 1996). Controlled release fertilizers

were compared to water soluble fertilizer as to nutrient leaching in Marigold

plants (Cox, 1993). The controlled release fertilizer was only more effective thansoluble fertilizer at reducing leaching when applied in 2 small doses instead of

one (one at planting, the other 15 to 35 days later). Leaching is reducing byapplying the controlled release fertilizer rather than incorporating it in the

medium. In all fertilizer types and application methods NO3 was the

predominant type of N found in the leachate (Cox, 1993).

(11) immature

(unfinished) compostcan stunt or kill plants,

and reduce germination

and growth.

(Most composters don't do any testing of their compost. After a while, you'll get

a "sense"

of the look, feel, and smell of finished compost. For uses other than top-

dressing/mulch,

immature (unfinished) compost may stunt or kill plants. Therefore, the grower

should

determine compost maturity before using compost as a growing media or

incorporating compost

into soils.

The simplest of testing method is to put your compost in a couple of pots and

plant some radish

seeds in the compost. If 3/4 or more of the seed sprout and grow into radishes,

then your compost

is ready to use in any application. Radishes are used because they germinate

(sprout) and mature

quickly. If you want to conduct more scientific tests of your compost, follow the



three simple

procedures outlined below.)

This web site and tutorial was created under the auspices of Sarasota County

Government

Environmental Services Business Center Solid Waste Division

<http://www.co.sarasota.fl.us/solid_waste/>, Resource Conservation Section,

with

innovative recycling grant funds provided by the Florida Department of

Environmental

Protection <http://www.dep.state.fl.us>. Content for this site was provided by

Resource

Management Group, Inc. <http://recyclesmart.com>, with web design by R.W.

Beck,

Inc. <http://www.rwbeck.com>

The Composting Tutorial is based on the Master Composter Handbook

developed by Hillsborough

Cooperative Extension Service through a grant from the Hillsborough County

Solid Waste

Management Department <http://www.hillsboroughcounty.org/solidwaste/home.html>.

(12) Casts increase plant dry weight and N,

P, Mg and K uptake

from the soil.

Effect of Casts on Plant Growth (continued)

The application of earthworm casts (0, 100, and 300 g per 3.5 kg soil) increasedthe dry weight of soybean by 40 to 70%. The nitrogen absorbed by the plants

from the soil increased to 30 to 50%. Phosphorous and potassium in the plant

were twice that of the control. The amount of organic matter, total nitrogen,

phosphorous and potassium in the soil also increased, as well as available phosphorous and potassium in the soil (Lui et al., 1991). The presence of

earthworm casts increase the uptake efficiency of nitrogen as shown in Zhao et

al. (1988) where the addition 15N labeled chemical fertilizer mixed withearthworm casts increased the nitrogen utilization coefficient from 22.4 to 38.4%and that of the N-P fertilizer from 33.2 to 40.9%. In Hidalgo (1997) media: casts

ratios of 1:1, 2:1 and 3:1 increased growth index, stem diameter, root growth, dry

weight, flower initiation and flower number compared to peat moss: perlite (7:3)and pine bark: sand (4:1). Earthworm casts were found to increase nutrient

uptake in Tomati (1994), including nitrogen and several ions, particularly Mg



and K.

(13) Casts contain the

necessary nutrients for

plant growth: whenadded in sufficient

amounts, as in 4-10 Kg

casts / m2 , casts can

outyield NPK fertilizers(100 Kg N / m

2 ).


In Saciragic et al. (1986) plants were given NPK or 2-10 kg casts m-2

. Cabbagesgiven 4 kg casts leeks given 10-kg casts outyielded the NPK controls. Fodder

sorghum given 10 kg of compost and cut twice yielded only 60% as much dry

matter as when given NPK (110-kg N m-2

). It was concluded that foddersorghum required fertilizer as well as. Casts are not only used in horticulture, but

in agronomic crops too.

(14) Casts have a

hormone like effect that

increase germnination

and growth rate.


Indole compounds were detected in the worms, but it was not possible to identifyspecific auxins (Hidalgo, 1997). When used in horticulture, earthworm casts

have a hormone-like effect. The biological effect of casts is linked to microbial

metabolites that influence plant metabolism, growth and development (Tomati etal., 1997). Casts of the earthworm Eisenia fetida andrei increased germination

rate and enhanced seedling growth of cucumber seeds in Hidalgo (1999), and it

was concluded that studies are needed to determine if casts contain the plant-

growth- promoting hormones and available nutrients necessary to enhancegermination and plant growth.

(15) As feed passesthrough the earthworm

gut the material is

mineralized and plantnutrients are available.

Production of Earthworm casts

As explained by Edwards (1995), earthworms ingest organic matter and egest itas much finer particles after passing through a grinding gizzard that they all

possess. Worms feed on the microorganisms that grow upon the organic material.

They take over the role of aerating necessary in composting to maintain aerobicconditions and their turnover rate is much higher than with composting as they process 3 feet deep layers of suitable organic material in less than 30 days

(Edwards, 1995). Edwards & Bates (1992) found Eisina fetida to be the best

choice due to its wide temperature and moisture tolerance, and because it is atough worm easy to handle and it out competes other species. Thee highest

growth rate in Eisina fetida at 30oC and 85% moisture. A maximum of cocoons

hatched at 20 o

C, which was considered optimum growth temperature for thisworm (Edwards & Bates, 1992)

During this process, N, P and Ca mineralized. Worms die at temperatures higher

than 35

o

C, and they process OM best at temperature between 15 and 25

o

C, and amoisture of 70 to 90%. Different materials are mixed before processing for

faster results and a better product. Also worms have a limited tolerance to some

chemicals. The most commonly used earthworm is Eisina fetida and the bestresults are obtained by using raised beds, feedstock is added at the top and casts

are collected at the bottom through mesh floors. In 25 kinds of vegetables, fruits

or ornamentals casts did better than compost or commercial potting mixes.(Edwards, 1995). There's scientific evidence that human pathogens do not



survive the vermicomposting process (Edwards and Bohlen, 1995).

(16)

As feed passes through

the earthworm gut the

material is mineralizedand plant nutrients are

available.

Effect of Ingestion by Earthworms

Many studies were conducted on the process by which earthworms

transform organic matter after ingesting it and on the properties of the

resulting material, but very few were based on stabilized casts, compared tosynthetic fertilizers and compost. Orozco (1996) investigated the ability of

Eisina Fetida, one of the most promising earthworms for vermicomposting,

to enrich coffee pulp through digestion. The ingested material had no

available C or N originally, but a minimum of 178 ppm of available nitrogen

and 0.86% extractable C were found in the casts, along with higher P, Ca

and Mg values, with a decrease in K content only. Earthworms increase

nitrogen mineralization rate (Pashanasi, 1992; Parmelee, 1988; Ruz-Jerez,

1992). Available N increased irrespective of the residues the earthworms

feed on or the growth temperature, which was attributed to the increase in

oxidized C due to soil ingestion, and not to change in soil texture since the

soil was not mixed (Ruz-Jerez, 1992). Binet (1992) found the consumptionof Rye grass by Earthworms to be 2.4-mg dry weight g-1

fresh mass of

earthworm day-1

, and 3 times more N was released in casts than in the soil

before ingestion, which represents 0.13 mg N / g live worm / day.

Furthermore a 10% N renewal in earthworm biomass in 85 days was

observed, meaning 10% of worm-biomass N was replaced by N from the

soil, and 28% of available N was due to N excretion. Extractable carbon

was found to increase in soil material ingested by earthworms, which was

explained by the possible effect of indigenous enzymes in the gut and the

incomplete resorbtion of organic C before excretion (Daniel, 1992). The

excreted polysaccharides in the earthworm gut (Arthur, 1963) could also be

responsible for this increase. According to Lavelle (1992) high levels ofammonium are found in fresh casts due to the excretion of NH4 through the

endonephridia gland into the gut, and the mineralization of soil organic

matter by the ingested soil microflora in the middle and posterior part of the

gut. Low NO3 in fresh casts show that nitrate isn't a metabolic product of

EW (Lavelle, 1992).

(20) Since high

temperature are not part

of the earthworm cast production process

disease suppressing

microorganisms thatmay be present in thismaterial survives in the

absence of heat.

Plant pathogens: High temperatures are not part of organic matter processing by

earthworms and casts may inherently contain the microorganisms necessary fordisease suppression. Only a few studies have tested for suppression in earthworm

casts (Szczech, et al ., 1993) and a few others for disease suppression in the

presence of earthworms - Aporrectodea spp. (Stephens & Davoren, 1997;

Stephens et al ., 1994). Szczech & Smolinska (2001) showed a suppression of Phytophthora sp. by earthworm casts.

Foodborne diseases: Foodborne disease outbreaks traced to fresh fruits and

vegetables are increasingly recognized in the US. For example, a recent literaturereview cites twice as many produce-related foodborne disease outbreaks between



1988-1992 as in the five year period prior to 1988 (Buck et al., 2003). The risk

of product contamination with foodborne pathogens is a concern for farmersusing organic or conventional methods of agriculture alike. The primary source

of produce contamination in the field is believed to be either the irrigation water

or a soil (amended with manure) reservoir. Earthworms have been exploited to

accelerate biodegradation of organic wastes from farms. Previous experimentsdemonstrate that Enterobacteriacea including Salmonella are not isolated from

the gastrointestinal tract of earthworms, even when worms are raised in heavilycontaminated environments (Finola et al., 1995). This data would suggest that

many Gram negative bacteria, such as those responsible for many of the

foodborne diseases, do not survive passage through the gastrointestinal tract of

the earthworm.

(21) Some composts are

suppressive of plant

pathogens but heatingthem to 60 C for fivedays reduced

suppressiveness. This is

why some composts needto be inoculatedwith

disease suppressing

microorganisms.

Adding nutrients (i.e.

reducing competition)

also reduces disease suppression by

composts.

Suppression of soil borne diseases has been reported for several kinds of

composts (Chung et al . 1988). Abbasi et al. (2002) demonstrated reduced

bacterial disease and anthracnose on fruit and increased yield in organically- produced tomatoes produced in soil amended with compost. Both compost and

manure were also shown to influence populations of plant parasitic and free-

living nematodes in transitional organic soil cropped to tomatoes (Nahar et al2004). Populations of plant parasitic nematodes, primarily Pratylenchus

crenatus, were inversely correlated with populations of fungal- and bacterial-

feeding and omnivorous nematodes, and with soil organic matter content. Chen

et al. (1987) showed that heating suppressive composts to 60C for five daysdestroyed suppression. Suppressiveness was also reduced when nutrients were

added to the planting mixture, which is consistent with the hypothesis that

nutrient competition between the compost microflora and the pathogen Pythium

spp. contributes to disease suppression (Mandelbaum and Hadar, 1990). Certaintypes of composted pine bark suppressed Pythium damping-off diseases when

incorporated into planting mixes (Boehm et al., 1993). Since an increase in

temperature is part of the composting process, it is sometimes necessary toinoculate composts with beneficial microorganisms (Hoitink et al ., 1993).

(22) A compost pileneeds to be 3 cubed feet

to hold heat in winter

and takes 3-4 months to

be cured

OSU extension: A large compost pile insulates itself and holds the heat ofmicrobial activity. Its center will be warmer than its edges. Piles smaller than

three feet cubed (27 cu. ft.; 3-4 ft tall) have trouble holding this heat in the

winter, while piles larger than five feet cubed (125 cu. ft.; 5-6 ft tall) do not allow

enough air to reach the microbes at the center. These proportions are ofimportance if your goal is fast, high temperature composting. Large piles are

useful for composting diseased plants or trees as the high temperatures will kill

pathogens and insects.



Moisture and Aeration

[...] The larger the pile, the higher the temperature and the faster the composting

proceeds, but only up to a certain point. At temperatures higher than 160 degreesF, composting slows down and charring or burning begins. This can become a

problem in dry composts, particularly in the summer.

How to Prepare and Use Compost

Remove grass and sod cover from the area where you construct your compost pile to allow direct contact of the materials with soil microorganisms. The

following "recipe" for constructing your compost heap is recommended for best

results:

After 3-4 weeks, fork the materials into a new pile, turning the outside of the old

heap into the center of the new pile. Add water if necessary. It is best to turn your

compost a second or third time. The compost should be ready to use within threeto four months. A heap started in late spring can be ready for use in the autumn.

Start another heap in autumn for use in the spring.

You can make compost even faster by turning the pile more often. Check the

internal temperature regularly; when it decreases substantially (usually after

about a week), turn the pile.

(23) Organic debris aremore palatable to

earthworms if it’s fresh

or incubated for up to 2

weeks. The particle sizeof organic matter

doesn’t matter.

In Martin et al. (1992) it was shown that when fresh material is compared toincubated material, worms prefer fresh organic matter as in undecomposed plant

debris or debris incubated for 2 weeks. Incubation of the material fed to

earthworms for 2, 5 and 10 weeks caused an increase in growth rate and yield

efficiency. With fresh plants (or plants incubated for 10 weeks or less) wormseat less and gain more weight than with material incubated for more than 10

weeks.

Martin et al. (1992) states that worms prefer leaves to roots: When leaves are

incubated for more than 10 weeks however the material becomes only as

beneficial as fresh root material: plant material decomposed for a long time hasless nutritive value. When roots are incubated for 2-5 weeks they increase

growth rate, but without a change in yield efficiency. This was explained by the

fact that fresh OM has a higher water-soluble content and more N availability.

Also in the same study all plant material have the same value after a longincubation time since all easily assimilable compounds are gone. When legumesand grass were compared they gave different yield efficiency results although

they both have same N content because legumes have higher nitrogen

assimilability.

As to the particle size effect, a fraction of soil OM was replaced with labeled C

- OM. The results showed that worms ingested similar amounts of coarse OM



(young OM – 250 – 200 µm) and fine OM (0.20µm). This indicates that particle

size does not matter (Martin et al. , 1992).

(24) Earthworms haveless requirements than

microbes in processing

carbon and nitrogen.

Although high amounts of low molecular weight proteins encourage microbialgrowth and consequently mineralization there's a possibility that earthworms

have lower requirements than microbes in processing C and N (proteins

included) since material that goes through the earthworm gut show a highermineralization rate than in the case where it's just incorporated in the soil (where

decomposition occurs through microbes); Devliegher and Verstraete (1996)

studied the effects of nutrient enrichment processes (i.e. allowing the passage of

organic residues from the surface of the soil to below the surface) and those ofgut associated process (i.e. enzymatic activities in the earthworm gut that

increase the nutrient content of the ingested residues). They concluded that if the

weight-increase of the worms is accounted for, the nutrient content of ingested

organic material largely makes up for the nutrient content of the same materialwhen simply incorporated in the soil. Therefore we might assume that earthworm

have less restrictions than microbes on protein quality and carbon to protein ratio

as related to decomposition of organic matter.

(25) High salinity levelsand alkalinity harm

earthworms.

Earthworms are also

sensitive to pesticides.

A pH of 8.5 and electrical conductivity of 8 dS m-1 were found to harmearthworms. Alklainity and salinity are harmful to both earthworms and

microorganism (Santamaria-Romero et al ., 2001). Worms can be used to assess

the environmental effects of chemicals because they can predict the effect of

chemicals on other soil invertebrates. The survival rate of earthworms when atoxic chemical is added to the soil would then be the indicator of the level of

toxicity of this chemical Edwards et al. (1992).

Edwards et al. (1992) states that pesticides tested on worms in labs are more

consistent since a standard number of worms from the same species is in intimate

contact with the pesticides. Still soils with different absorbing capacities have been used. He also considers that the unvalid methods would be applying a

chemical directly to the earthworms (the results would be unrealistic), mixing a

chemical with the earthworm food (due to food repellency problems) and

injecting the tested chemical into the earthworm, since this can cause direct

injury and falsify the results.



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OVERVIEW OF EARTHWORM CASTS AND A COMPARISON WITH COMPOST

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