Compost and Vermicompost as Amendments Promoting Soil Health

Full text

31
Compost and Vermicompost as Amendments
Promoting Soil Health
Allison L.H. Jack
1
and Janice E. Thies
2
Q1
1
Department of Plant Pathology Cornell University, New York, USA
2
Department of Crop and Soil Sciences, Cornell University, New York, USA
CONTENTS
31.1 Definitions of Traditional Compost and Vermicompost.......................................... 454
31.2 Review of Research Findings ....................................................................................... 456
31.2.1 Historical Overview ........................................................................................ 456
31.2.2 Plant Growth Promotion: Integrated Nutrient Management .................. 457
31.2.3 Plant Disease Suppression ............................................................................. 458
31.3 Some International Experience with Composting
and Vermicomposting ................................................................................................... 460
31.3.1 Cuban Experience............................................................................................ 460
31.3.2 Indian Experience............................................................................................ 460
31.3.3 Australian Experience..................................................................................... 461
31.4 Discussion........................................................................................................................ 462
References ................................................................................................................................... 463
Before the advent of modern industrialized agriculture, farmers relied almost entirely
on raw and composted animal manures and agricultural residues as soil fertility
amendments. Now, post-Green Revolution, scientists are shifting their focus away from
agricultural systems that rely on synthetic fertilizers and pesticides, toward systems that
incorporate the use of composted organic materials. A growing understanding of the
complex ecological mechanisms producing the observed soil and plant growth benefits
of traditional soil amendment methods prompts this. Practitioners, researchers and
entrepreneurs in both developed and developing nations are experimenting with novel
composting technologies, using a wide variety of organic materials, and reporting positive
results (Bailey and Lazarovits, 2003; Arancon et al., 2003; Bhadoria and Prakash, 2003).
The current emphasis on composting as a means to stabilize manure comes from
increasing public concern over nutrient run-off and the eutrophication of aquatic
ecosystems associated with the over-application of raw animal manures to soils.
Composting animal manures and plant residues can increase bulk density, kill weed
seeds, and decrease the levels of human and plant pathogens. However, the composting
process can lead to an overall loss of nutrients compared to the starting material
(Sommer, 2001). This potential drawback could be outweighed by the increased benefits
453

to plants and the environment, which are beginning to be quantified and understood.
For example, a recent field study comparing the effects of fresh vs. thermally composted
swine manure on the growth and yield of corn showed a 10% increase in yield, and up to
a 15% increase in aboveground biomass for plants receiving the composted manure
treatment (Loecke et al., 2004). In this study, treatments were normalized for total
nitrogen (N) content, so the increased yield could not be explained by a difference in the
overall quantity of N applied, although differences in the chemical form of N might have
affected plant availability. Soil physical and biological factors, including the microbial
communities that the composted material benefited, were probably responsible for the
increased yield in this case.
This chapter presents an overview of the current understanding of how both traditional
compost and the recently popularized vermicompost affect plant growth and overall plant
function. Experience from three countries in different parts of the world is reviewed to
illustrate the beneficial use of compost in sustainable agricultural systems.
31.1 Definitions of Traditional Compost and Vermicompost
There are two major categories of compost: those that incorporate a biologically driven
heating phase and those that do not. The first category will be referred to here as
traditional compost, while vermicomposting will be used as the primary example of the
latter category (Figure 31.1).
Traditional compost is the stabilized product of the decomposition of plant and animal
residues at high temperatures (40–708C) by the activity of thermophilic (heat-loving)
microorganisms. The traditional composting process involves an initial stage conducted at
moderate temperatures (10–408C), during which labile organic matter is rapidly
consumed by mesophilic microorganisms, followed by a stage when thermophilic
Time
T (deg C)
I. Acclimatization
III. Curing
I. Mesophilic II. Thermophilic III. Cooling IV. Curing
Thermal
Compost
10
40
70
I. Mesophilic II. Thermophilic III. Cooling IV. Curing
Mesophilic
Thermal
Compost
Thermophilic
II. Hydrolytic
Vermicompost
FIGURE 31.1
Theoretical time vs. temperature curves for thermogenic (thermal) compost and vermicompost. Arrows represent
major phases in the composting process. Phases for thermal compost are adapted from Chefetz et al. (1996) and
those for vermicompost are adapted from Benitez et al. (2000).
Biological Approaches to Sustainable Soil Systems454

microorganisms drive the temperatures up to 608C at which point lipids, proteins and
complex carbohydrates are consumed and broken down. During the final curing stage,
when the material cools down, mesophilic organisms are able to recolonize and break
down the remaining recalcitrant organic matter (Chefetz et al., 1996).
The vermicomposting process has been described as “biooxidation and stabilization of
organicmaterialinvolving thejointactions of earthworms and (mesophilic) microorganisms”
(Aira et al., 2002). In contrast to traditional compost, vermicompost never heats up much
above ambient temperatures. Many feedstocks can be used directly in vermicomposting
systems; however, animal manures can drive temperatures into the thermophilic range
during decomposition, which can kill compost earthworms. Many practitioners combine the
two techniques, initially doing a partial precomposting at high temperatures followed by a
finishing stage of vermicomposting (Frederickson et al., 1997). The phases in vermicompost-
ing involve a period where worms acclimatize to the substrate that they are placed in. There is
a hydrolytic phase in which readily degradable organic matter is broken down, and then a
curing phase where the more recalcitrant organic matter is broken down (Benitez et al., 2000).
More information on the vermicomposting process is provided in Aranda et al. (1999).
Microbes living in traditional compost effectively go through a selection event during
the heating phase where the material is populated by only specially adapted thermophilic
bacteria, most of which are as of yet uncultured (Dees and Ghiorse, 2001). The microbial
community in finished traditional compost is derived from microbes that are facultative
thermophiles and can survive in mesophilic temperatures, surviving the hot phase by
forming spores or recolonizing during the mesophilic curing stage. Vermicompost, on the
other hand, maintains a wide diversity of organisms throughout the entire process,
including saprophytic bacteria and fungi, protozoa, nematodes and microarthropods.
There is evidence that the compost worm Eisenia fetida has unique indigenous gut-
associated microflora (Toyota and Kimura, 2000) which could be contributing to the
microbial community in cured vermicompost.
Earthworm fecal pellets, or casts, are different from traditional compost in that they are
covered with a mucus layer generated by the worms’ intestinal tract. This layer provides a
readily available source of carbon for soil microbes and leads to a flush of microbial
activity in freshly deposited casts. The effects of earthworm-derived polysaccharides on
soil microbial populations are reviewed in Brown et al. (2000). Polysaccharides of plant,
bacterial, fungal origin have been shown to enhance soil aggregate stability (Oades, 1984).
Several recent studies have investigated the effect that polysaccharides of earthworm
origin may have on the physical aspects of soil as well as the documented effects on soil
microbiota (Albiach et al., 2001; Ge et al., 2001).
The microbial communities in traditional compost and vermicompost are thought to be
distinct because of the differences between the two processes just described. However,
many of the studies carried out so far have used composts made from different feedstocks
(raw organic materials). This makes it difficult to determine whether the resulting
microbial community differences are due to the respective composting processes or are an
artifact of the starting materials. A culture-based study using Biolog plates (Biolog Inc.,
Hayward, CA, USA) found that microbial populations in vermicomposts were able to
metabolize a greater number of single C substrates than microbial populations in
traditional composts made from different feedstocks (Atiyeh et al., 2000b). This implies a
greater metabolic diversity in the culturable bacterial communities in vermicompost.
It should be pointed out, however, that culturable soil microbial communities
represent only a small fraction of the total communities present, so other research
techniques are needed to access a greater proportion of the total microbial community
(Hill et al., 2000). Several separate studies using molecular techniques to track microbial
communities have shown that traditional composts and vermicomposts have strikingly
Compost and Vermicompost as Amendments Promoting Soil Health 455

different taxonomic groups present; however, the composts used in these studies were
prepared from different types of feedstocks (Alfreider et al., 2002; Verkhovtseva et al.,
2002; Schloss et al., 2003).
The entire field of soil microbiology is rapidly expanding as new techniques provide
greater insight into the structure and function of soil microbial communities. Our
understanding of compost microbiology should increase greatly as researchers use more
of these techniques to assess the differences between traditional and vermicompost and
between composts made from different feedstocks, relating this information to their
overall effects on soil and plant function.
31.2 Review of Research Findings
31.2.1 Historical Overview
The oldest recorded mention of the use of manure in agriculture is on clay tablets from the
Akkadian Empire of the Mesopotamian Valley nearly 4500 years ago, and both the Greeks
and the Romans wrote about compost (Rodale, 1960). Sir Albert Howard is widely
considered the father of modern scientific composting through his pioneering research and
international work in the early 1900s in India where he helped develop the Indore method
of compost production (Howard, 1943). Rodale, champion of organic farming and founder
of the Rodale Institute in Kutztown, PA, USA, continued Howard’s work and published
several classic, still relevant texts on composting in the USA (Rodale, 1945, 1960).
Traditional compost has been widely used as a potting mix amendment in the
horticulture, turf, landscaping and nursery industries for decades (Roe, 1998), but it is
rarely used on field crops in industrialized nations. Very little recent scientific information
is available on the large-scale field application of composts, although some research is
beginning to appear on this topic, most notably in developing nations such as India, as
discussed later in section 31.3.
Although the 1960 edition of Rodale’s book of composting contains an entire chapter on
home and farm production of earthworm compost, vermicomposting on a commercial
scale is a more recent practice. Large-scale vermicompost production was pioneered by
Clive Edwards who worked on developing the continuous flow-through reactor design at
the Rothamsted Experimental Station in the 1970s, and the industry has been growing ever
since. Edwards has contributed greatly to the scientific literature on vermicompost
production and use (Edwards et al., 1984; Edwards and Neuhauser, 1988) as well as to
general earthworm ecology (Edwards, 2004).
In the United States, vermicompost is most commonly used as a potting mix amendment
for cultivating vegetables, ornamentals and seedling starts. It is primarily marketed to
home gardeners in small, highly packaged quantities through horticulture catalogues and
retailers. Prices run up to 10 times those for traditional compost, which leads to the image
of vermicompost as a “luxury” soil amendment. However, in developing nations, both
traditional compost and vermicompost are applied to field soil at rates of several t ha
21
in
an effort to decrease dependence on synthetic fertilizers and pesticides and to replace
organic matter lost through years of intensive conventional farming.
31.2.2 Plant Growth Promotion: Integrated Nutrient Management
When traditional composts and vermicomposts have been compared directly with respect
to their chemical characteristics, vermicompost has been shown to be a potentially better
Biological Approaches to Sustainable Soil Systems456

growth medium amendment than traditional compost based on such analyses
(Vinceslas-Akpa and Loquet, 1997; Chaoui et al., 2003). In one study, woody plant
materials were composted using both thermal composting and vermicomposting, and the
chemical composition of the organic matter in the resulting composts was compared using
NMR spectroscopy (Vinceslas-Akpa and Loquet, 1997). The organic matter in the
vermicompost was more humified and had undergone more lignolysis compared to the
traditional compost.
This result indicates that vermicompost is a more stable form of organic matter than the
thermal compost, and thus less likely to immobilize N when used as a growth medium
amendment. In another study, vermicompost was shown to be a slower-release fertilizer
than traditional compost, giving an extended release of N over time, which reduces the
risk of nutrient leaching in container-based systems (Chaoui et al., 2003), although it is not
known if the composts used in this study were made from the same type of feedstock. In
the same study, vermicompost also had a lower risk of causing salinity stress in plants
when compared to traditional compost.
Some of the more interesting effects of both traditional and vermicompost on plants are
nonnutrient related and point to the possibility that using composts may be a sustainable
way to increase biological soil health. Experiments have shown that vermicompost in both
solid and liquid forms promotes plant growth (Buckerfield et al., 1999) and enhances
seedling germination (Ayanlaja et al., 2001). With all mineral nutrients held equal, the
addition of as little as 10–20% vermicompost to the growth medium resulted in significant
increases in plant biomass and yield in greenhouse tomatoes (Atiyeh et al., 1999) and
marigolds (Atiyeh et al., 2002b). More compost is not necessarily better in this case, as
plants grown in 100% vermicompost were significantly smaller than the controls (Atiyeh
et al., 2000a).
Subsequent field studies carried out by the same research group found that 5–
10 t ha
21
applications of vermicompost significantly increased marketable yields of
pepper, tomato and strawberry when compared to synthetic fertilizers (Arancon et al.,
2003). Plant growth promotion depended on the type of feedstock used; vermicom-
posted cow manure consistently gave the highest yields compared with food-waste and
paper mill-waste vermicomposts (Arancon et al., 2003). A subsequent greenhouse
comparison of traditional vs. vermicomposts found an inconsistent growth-promoting
effect compared to a Metro-Mix control (Atiyeh et al., 2000b). However, the same study
did find a significant growth-enhancing effect when 20% vermicompost was added to
soil and used to grow raspberry plants. Vermicomposted pig manure solids gave the
highest plant biomass when compared to vermicomposted food waste and to
traditionally composted biosolids, leaf waste, yard waste, bark, and chicken manure
(Atiyeh et al., 2000b). No clear conclusions about the plant growth-promoting effects of
different composting processes (thermal and vermicompost) can be made until composts
made from the same feedstock are compared.
Humic acids extracted from vermicompost have been shown to promote plant
growth (Atiyeh et al., 2002a) as well as physiological changes in plant roots including a
greater number of sites of lateral root emergence and greater total root area (Canellas
et al., 2002). One of the ways that humic acids are thought to enhance plant growth is
by binding plant-growth hormones present in the soil. The contributions of
phytohormones to plant growth and health have been discussed in more detail in
Chapter 14. Auxin (indole acetic acid, or IAA) has been extracted from traditional
compost (Garcia Martinez et al., 2002) and has been detected in humic acid complexes
in vermicompost (Canellas et al., 2002). Auxin is present in the soil solution partly due
to the action of certain groups of rhizobacteria referred to as plant growth-promoting
rhizobacteria (PGPR). These are soil bacteria that aggressively colonize plant roots and
Compost and Vermicompost as Amendments Promoting Soil Health 457

have been shown to promote plant growth and suppress plant disease. PGPR that
produce auxin-like compounds have been isolated from traditional composts (De Brito
Alvarez et al., 1995) and are thought to contribute to the increased plant growth
observed with compost amendments.
In addition to bacteria that secrete plant-growth hormones, PGPR include associative
nitrogen-fixing bacteria and phosphate-solubilizing bacteria, considered in Chapters 12
and 13. Associative nitrogen-fixing bacteria such as Azospirillum spp. do not enter the
plant root or form root nodules as in the classic Rhizobium –legume symbiosis, but they fix
atmospheric N
2
into cellular amino acids, which are subsequently mineralized into plant-
available N forms (ammonium and nitrate) upon cell death. Phosphate-solubilizing
bacteria convert mineral forms of P into soluble, plant-available forms as discussed in
Chapter 13. Although research in this field is expanding, there has been limited
commercialization of PGPR as biofertilizers. Finding strains that will perform consistently
in different plant cultivars and under different field conditions is an ongoing challenge, but
there is great potential for the use of PGPR to help reduce dependence on synthetic
fertilizers (Vessey, 2003).
Other microorganisms that are associated with the plant-growth promotion effect of
composts are the arbuscular mycorrhizal fungi (AMF). As discussed in Chapter 9, AMF
colonize plant roots and form a symbiotic relationship that facilitates plant nutrient
uptake in exchange for photosynthetically-derived carbon (C). AMF colonization of rice
(Kale et al., 1992) and sorghum (Cavender et al., 2003) was found to increase
significantly with vermicompost applications, and AMF colonization has also been
correlated with traditional compost applications (Tarkalson et al., 1998), although this
relationship has not been studied in depth. In the case of sorghum, plant growth was
actually found to decrease with vermicompost applications, even though there was an
increase in AMF colonization. This could be due to the plants not being nutrient-limited
during the experiment, so the AMF colonization was more parasitic than beneficial
(Cavender et al., 2003).
Both composts and biofertilizers can be used in Integrated Nutrient Management
(INM) schemes, where lower rates of synthetic fertilizers are applied in conjunction
with use of organic or biological amendments. In a recent field study in India,
researchers found that providing rice with 50% of its N requirement from synthetic
fertilizer and 50% from vermicompost, with the addition of Azospirillum lipoferum and
Bacillus megaterium var. phosphaticum as biofertilizers, could increase yields up to 15%
compared with the control (receiving 100% of the recommended dose of synthetic
fertilizer N) (Jeyabal and Kuppuswamy, 2001). Since organic amendments and
biofertilizers were not tested separately, it is impossible to draw conclusions on how
much of the observed effect was due to the vermicompost or the manure treatments
alone. Further evidence of the benefits from INM is found in a greenhouse study from
Venezuela where vermicomposted cow manure and coffee pulp composed up to 45%
of the potting medium for papaya plants. Plant growth in treatments with a mixture of
intermediate amounts of synthetic N fertilizer and vermicompost was higher than in
treatments with the full rates of one or the other source of nutrients (Acevedo and
Pire, 2004).
31.2.3 Plant Disease Suppression
Traditional composts have widely documented plant disease-suppressive properties and
are a common component of potting media used in greenhouse production systems
(Hoitink and Fahy, 1986; Hoitink and Kuter, 1986; De Ceuster and Hoitink, 1999). Liquid
Biological Approaches to Sustainable Soil Systems458

preparations of compost, known as compost teas, have also been shown to prevent various
plant diseases (Weltzien, 1992; Scheuerell and Mahaffee, 2002). Less widely known are the
disease-suppressive qualities of vermicompost. The addition of vermicompost to growth
media has resulted in the significant suppression of the following plant diseases: damping
off (Pythium, Rhizoctonia) (Chaoui et al., 2002); wilts (Verticillium) (Chaoui et al., 2002),
Fusarium (Szczech et al., 1993); root rot (Phytophthera) (Szczech et al., 1993; Szczech and
Smolinska, 2001); club root (Plasmodiophora) (Szczech et al., 1993; Nakamura, 1996);
white rot (Sclerotium) (Pereira et al., 1996); and the sugar beet cyst nematode (Heterodera
schachtii)(Szczech et al., 1993).
A recent study showed vermicompost tea to be as effective in controlling bacterial
canker (Clavibacter michiganensis spp. michiganensis) in tomatoes as several commercially
available biocontrol agents, giving a 63% reduction in disease for inoculated seedlings
(Utkhede and Koch, 2004). Field trials have also shown a reduction in plant damage
between conventionally fertilized rice and rice fertilized with vermicompost at
equivalent NPK levels. The plants receiving the vermicompost treatment had
significantly less damage due to the brown plant hopper (Nilapavata lugens (Stal)
(Homoptera: Delpecidae)) and sheath blight caused by the fungus Rhizoctonia solani
compared with plants in synthetic fertilizer treatment, both with and without chemical
pest control (Bhadoria et al., 2003).
Disease suppression has been seen to vary depending on the type of feedstock. In one
trial, biosolids vermicompost was less suppressive toward Phytophthera than vermicom-
post made from sheep, horse or cow manure (Szczech and Smolinska, 2001). The observed
suppression was thought to be biological in nature because heat-sterilized vermicompost
was not found to be disease-suppressive (Szczech, 1999). In addition to their role in plant
growth promotion, PGPR isolated from traditional compost have been shown to inhibit
fungal pathogens in vitro (De Brito Alvarez et al., 1995).
There are several ways in which beneficial microbes such as PGPR can inhibit plant
pathogens. They can outcompete the pathogen for a nutrient source; they can directly
parasitize the pathogen; or they can stimulate the plant to make physiological changes
that will decrease its susceptibility to infection through a process known as Induced
Systemic Resistance (ISR) (Pieterse et al., 2003). One of the physiological changes induced
in plants by PGPR is an increased production of antioxidants. Scientists are just
beginning to make the connection between soil health, plant health and human health by
documenting cases of higher levels of antioxidants in foods grown without synthetic
pesticides (Carbonaro et al., 2002).
Along with the hormone-producing and nutrient-mineralizing strains of PGPR, many
PGPR have been shown to prevent a wide variety of plant diseases in greenhouse and field
trials. Many practitioners who are committed to limiting chemical pesticide use are
interested in using PGPR and other biocontrol agents as alternatives, as discussed in
Chapter 32. Even with the great potential documented in the scientific literature, very few
plant disease-suppressing PGPR are available commercially to growers (Nelson, 2004;
USEPA, 2004).
There is evidence that certain composts naturally contain many species of PGPR (De
Brito Alvarez et al., 1995), as well as plant-growth hormones such as auxin (Canellas
et al., 2002; Garcia Martinez et al., 2002). Owing to the complex microbial ecology of
composts, the presence of many strains of PGPR is not necessarily an indicator that
the compost as a whole will be suppressive to plant diseases (McKellar and Nelson,
2003). With increasing knowledge of compost microbiology, the use of compost could
potentially be a low-cost, sustainable way to inoculate agricultural soils with beneficial
bacteria that can biologically enhance plant growth.
Compost and Vermicompost as Amendments Promoting Soil Health 459

31.3 Some International Experience with Composting
and Vermicomposting
31.3.1 Cuban Experience
After the Cuban revolution of 1959 and the subsequent US embargo, Cuban agriculture
relied almost entirely on imports for maintaining its food and agricultural systems. At the
time, over half of the daily caloric intake of Cubans was obtained through imported foods.
To support the Cuban economy, the Soviet Union bought Cuban sugar at above world
market prices, and it provided synthetic fertilizers and pesticides, farm equipment and
fuel to support “modernization” of Cuban agriculture. The collapse of the USSR at the end
of the 1980s and a strengthening of the US embargo in 1992 led to a food security crisis in
Cuba. Historical circumstance thus created a nationwide experiment in more biologically
based agriculture, the results of which have been well documented (Funes et al., 2000;
Warwick, 2001).
The Cuban government responded to the crisis by enlisting the support of researchers
and practitioners to shift the national agricultural system toward low-input, organic,
small-farm and urban garden plots with an emphasis on civic participation. Traditional
compost and vermicompost have played important roles in this shift toward sustainable
agriculture along with regional small-scale production and use of various biocontrol
agents against both microbial and insect pests (Altieri, 1999). Already by 1993, Cuba had
197 large-scale vermicomposting centers that produced 93,000 t vermicompost year
21
from a mixture of cow manure, sugar cane press mud, coffee pulp, plantain waste and
municipal garbage feedstocks (Gersper et al., 1993). The Ministry of Agriculture estimates
that about 600,000 metric tons of vermicompost were produced in urban areas of Cuba in
2002, while approximately 4.4 million t of other organic soil amendments were used
(Nodals, 2004). The Ministry also stated that agronomic studies have documented yield
increases of up to 40% in various crops when vermicompost is substituted for synthetic
fertilizers (Vanasselt and Bourne, 2000), although none of these reports is accessible in the
USA. Chapters 32 and 33 report experience of Cuban researchers with the use of bacterial
and fungal inoculants in their own and other countries.
31.3.2 Indian Experience
There is a large sustainable agriculture movement in India that is seeking to combine
traditional knowledge with modern science. Understanding and using beneficial soil
organisms is part of the overall effort to reduce dependence on synthetic fertilizers and
pesticides (Sinha, 1997; see also Chapter 35). Many government and civil society groups
are promoting vermicomposting both as a system of waste management and as a valuable
soil amendment. Recent reports in the Indian Journal of Agronomy have been providing
evidence that vermicompost applications to field crops can significantly reduce synthetic
fertilizer inputs.
Researchers have found some synergistic effects from satisfying only 50–75% of the
crop’s recommended NPK need with synthetic fertilizer while providing the remainder
through vermicompost. A combination of synthetic and organic fertilizers has, in many
cases, resulted in higher yields than from either nutrient source used alone. Yields from
the integrated use of synthetic and organic fertilizers (traditional compost, farmyard
manure or vermicompost) that are comparable to or greater than those achieved with
100% recommended NPK fertilizer applications have been documented for rice (Jeyabal
and Kuppuswamy, 2001; Bhadoria and Prakash, 2003; Bhadoria et al., 2003), sunflower
Biological Approaches to Sustainable Soil Systems460

(Dayal and Agarwal, 1998), guinea grass (George and Pillai, 2000), forage oats (Jayanthi
et al., 2002), maize (Nanjappa et al., 2001), and wheat (Ranwa and Singh, 1999).
An economic analysis of the INM system has shown little benefit to small farmers if
vermicompost had to be purchased off-site from a commercial producer (George and
Pillai, 2000). In light of this finding, several Indian nongovernmental organizations such as
Morarka Rural Research Foundation (Morarka, 2000) and the Bharatiya Agro Industries
Q3
Foundations Institute for Rural Development have responded by training over a million
farmers in on-site vermicompost production (BAIF, 2004). Pune, India, the location for the
Bhawalkar Ecological Research Institute (BERI), is considered by some to be the
vermicompost capital of the world. BERI promotes the in situ use of deep-burrowing
earthworms for processing organic wastes in agricultural fields, as well as vermicompost-
ing toilets and other urban waste-management systems (BERI, 2004; Bhawalkar, 2004).
In addition to being used with field crops, vermicompost is being used in various tree
crops, including agroforestry systems. One case study describes the success of one farmer
who dug a small basin around each coconut palm tree and applied 5 kg of active
vermicompost as an initial inoculum, a thin layer of cow manure, and a layer of plant
debris as mulch. The mulch is replenished periodically, and vermicompost is continually
produced under each tree (OFAI, 2004). In teak production, vermicompost used in
combination with the ring basin irrigation method has led to increased growth of young
teak trees through nutrient additions and improved moisture retention (Koppad and Rao,
2004). Indian researchers and practitioners are also enriching vermicompost with different
species of PGPR, including nitrogen-fixing and phosphate-solubilizing bacteria, with
vermicompost serving as a substrate for producing and applying of biofertilizers (Kumar
and Singh, 2001). Emerging local systems for producing and distributing vermicompost
and biofertilizers in India are discussed in Chapter 45.
31.3.3 Australian Experience
Australia is home to one of the larger vermicompost equipment companies, VermiTech,
which manufactures large-scale, continuous flow-through, reactor-type vermicomposting
systems. Many of Australia’s agricultural soils are low in organic matter and have poor
water infiltration and water-holding capacities. Trials that VermiTech has carried out with
cooperating farmers on the effects of applying vermicompost to field soils have showed
potential for 3–5 t ha
–1
application of vermicompost to significantly decrease soil
compaction, measured as depth to 300 psi with a penetrometer (Patten, personal
communication). Another field trial showed the potential of the same application of
vermicompost to increase pH, cation exchange capacity (CEC), and soil organic matter
(SOM), but so far, no peer-reviewed studies have been published (P. Patten, personal
communication).
Vermicompost has the potential to become a useful soil amendment in the Australian
and New Zealand wine industries. Field trials carried out by Australia’s Commonwealth
Scientific and Industrial Research Organization (CSIRO) with vermicomposts made from
mixtures of grape marc waste, animal manure and other agricultural wastes have shown
significant increases in yield without decreases in fruit quality (Buckerfield and Webster,
1998). In one study, vermicompost was used as mulch under the vines, applied about two
inches deep and covered with a thick layer of straw. When vermicompost was applied
alone, there was no significant increase in yield; however, when the vermicompost applied
was covered with straw, there was a 56% increase in yield. The straw is thought to protect
the microorganisms in the vermicompost from UV radiation and desiccation. The
following fruit quality factors were measured: Brix (% sugar content), pH and titratable
acidity, none of which was adversely affected by vermicompost treatments (Buckerfield
Compost and Vermicompost as Amendments Promoting Soil Health 461

and Webster, 1998). The effects of the undervine vermicompost and straw combination
were still measurable two years after the original application, which enhanced the
economic return for the grower (Buckerfield and Webster, 2000). Papers in peer-reviewed
journals describing these trials are forthcoming.
Even with several successful field trials, grower adoption of this practice is relatively
low, however, owing to a lack of consistent quality-assured product and high cost
(K. Webster, personal communication). There has been some grower adoption of
vermicompost amendments in the US wine industry. One well-established worm farm
in Sonoma Valley, CA, charges $375 yd
23
for dairy-manure vermicompost and
recommends that it be used in very small amounts, just one small cup when planting
new vines (Anonymous, 2003). Outreach and extension efforts as well as market prices
and the availability of quality vermicompost will determine adoption rates and the ways
in which vermicompost is used by practitioners.
31.4 Discussion
Composts play an essential role in any type of sustainable agricultural system, effectively
recycling municipal, industrial or agricultural wastes and residues, and returning organic
matter to the soil ecosystem. Adding organic matter to soils can relieve compaction and
increase aggregate stability, thus greatly improving soil structure, which has favorable
effects on soil biota. Composting processes, both traditional and vermicomposting, can
reduce the number of human and plant pathogens present in many types of organic
residues before they are applied to agricultural soils. The complex microbial communities
in high-quality cured compost have the ability to increase plant growth and decrease the
incidence of plant disease, reducing the need for synthetic fertilizers and pesticides.
Compost applications, both in research and in practice, are demonstrating that they can
increase soil health and therefore the overall sustainability of food-producing systems.
The future of compost use in sustainable agriculture will depend on collaborative efforts
among researchers, entrepreneurs and practitioners. Groups in the United States such as
the US Composting Council, the Cornell Waste Management Institute, and JG Press, the
publishers of BioCycle magazine and Compost Science & Utilization, are providing
channels for communication among these groups. Two US Department of Agriculture
programs, Associated Technology Transfer to Rural Areas (ATTRA) and Sustainable
Agriculture Research and Education (SARE), have compiled and disseminated extensive
information on composting.
Several international conferences have contributed to the growing scientific base of
knowledge such as the International Symposium on Composting and Compost Utilization
in Columbus, Ohio, held in 2002, and the First International Soil and Compost Eco-biology
(SoilACE) Conference convened in Leon, Spain, in 2004. A number of international NGOs
are carrying out compost research and extension on a large scale. Even with so much
international interest in compost science and use, much of the information available on
producing and using compost is difficult to access. It is scattered throughout numerous
trade journals, scientific journals from widely varying disciplines, diverse Internet sites, or
is passed on entirely by word of mouth.
Books published recently in Europe (de Bertoldi et al., 1996; Insam et al., 2002) are
helping to assemble and disseminate available scientific and practical information on
compost production and use. Increased attention by governments, NGOs and agribusi-
nesses to the role of compost in sustainable agriculture will contribute to the development
of new and better compost technologies. More mechanistic (laboratory) and empirical
Biological Approaches to Sustainable Soil Systems462

(field) studies on the production and use of composts will be mutually reinforcing.
Knowledge of actual practices and their effects can help keep laboratory experimentation
relevant, and a mechanistic understanding of the beneficial effects that composts have on
soils and plants should help drive innovative new practices.
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Author Queries
JOB NUMBER: 12276
Title: Compost and Vermicompost as Amendments Promoting Soil Health
Q1 Please check affiliation of Allison L. Jack.
Q2 Morarka (2004) is uncited, kindly provide details.
Q3 Morarka (2000) is citeed in text kindly provide reference list.