soil fertility; antioxidant activity; lettuce. Jen-Hshuan Chen, Yu-Chung Tsai
Department of Soil and Environmental Sciences,
National Chung Hsing University, Taichung, Taiwan, ROC.
Vermicomposting is the combination action of earthworms and microorganisms that can convert agricultural wastes into vermicomposts. It is not only more easily controllable, cost effective, energy saving, and no waste process, it also accomplishes most efficient way of recycling of organics and nutrients. Vermicompost is a nutrient-rich organic fertilizer and soil conditioner, its quality maybe determined by many factors, including the degree of earthworm activity, the conditions in which they have been exposed, and the composition of the organic wastes used. This paper reviews the current state of knowledge on vermicomposting and vermicompost . A pot experiment of lettuce was conducted to compare the effects of vermicomposts, chemical fertilizers, composted animal manures, and vermicompose combined with vermicompost tea application on soil fertility, antioxidant activity and growth of lettuce.
Keywords: Vermicompost, vermicompost tea;
Huge quantities of animal manures from livestock farms, and organic wastes from agro-industrial areas, have become a serious global problem. The conventional disposal system for wastes material, such as open dumping, land filling, was not sustainable due to leaching of certain toxic chemicals and heavy metals, have resulted in environmental pollution. There is a need for a safe technology to manage these organic wastes, and the technologies must be ecologically sound, economically viable and socially acceptable (Suthar, 2008). Organic wastes are often rich in plant nutrients. For example, studies have shown that about 70 – 80 % of the nitrogen (N), 60 - 85 % of the phosphorus (P2O5), and 80 % of the potassium (K2O) fed to animals are excreted in the manure, depending on the animal species (Klausner et al., 1984). Therefore, organic wastes have the potential as the raw materials of fertilizers. Converting organic wastes into high quality composts by composting has resource recycling benefits, cconventional composting has been adopted as a good way for the reduction and recycle of wastes, and vermicomposting is emerging as an appropriate alternative to conventional vermicomposting.
Earthworms have been used in the vermiconversion of urban, industrial and agro- wastes to produce vermicpompost (Gupta and Garg, 2008; Sangwa, et al., 2008;,Tsai, 2016). Earthworms can be cultured and put to various uses i.e. to improve and maintain soil fertility, to convert organic wastes into manure, to produce earthworm based protein food (earthworm meal) for livestock, drug and vitamins source, as natural detoxicant and a bait for fish market (Satyawati, et al., 2005)
VERMICONPOSTING AND VERMICOMPOST
Vermicomposting as a principle originates from the fact that earthworms while in the process of feeding fragment the substrate thereby increasing its surface area for further microbial colonization. It is an aerobic, bioxidation and stabilization non- thermophilic process of organic waste decomposition that depends upon earthworms to fragments, mix and promote microbial activity.
Vermicompost is the product or process of organic wastes degradation using earthworms, to create a heterogeneous mixture of decomposing organic wastes (excluding meat, dairy, fats, or oils), bedding materials, and vermicast. Vermicast, also known as worm casting, worm humus or worm manure, is the end-product of the breakdown of organic matter by species of earthworm.
Vermiculture and vermicomposting are similar but different. Vermiculture is the culture of earthworms and to continually increase the number of worms in order to obtain a sustainable harvest. Vermicomposting is the combination action of earthworms and microorganisms that can convert organic wastes into a humus-like material known as vermicompost. The goal is to process the material as quickly and efficiently as possible. (Glenn Munroe, 2005). However, if we want to have high production of vermicompost with high quality, we must know how to operate a successful vermicomposting. It is very important we should keep in mind that earthworms lack lungs or other respiratory organ, the O2 is diffused from their skin; they are photosensitive creatures with no nose, no ears, no bones and no teeth.
Key requirements for successful vermicomposting
Decide the types of vermicomposting systems
There are three basic types of vermicomposting systems, including windrows, beds or bin, and flow-through reactors. Windrows and bins can be either batch or continuous-flow system, while all flow-through systems are of continuous flow variety. Batch systems are ones in which the bedding and food are mixed, the earthworms added, and nothing is done until the process is complete. Continuous-flow systems are ones in which earthworms are placed in bedding, whereupon feed and new bedding are added incrementally on a regular basis (Glenn manroe, 2005).
Use suitable earthworm
Earthworms are classified into three main ecophysiological categories: (1) leaf litter- or compost-dwelling worms, live at soil-litter interface and eat decomposing organic matter (called Epigeic) e.g. Eisenia fetida; (2) topsoil- or subsoil-dwelling worms that feed (on soil), burrow and cast within soil, creating horizontal burrows in upper 10–30 cm of soil (called Endogeics); and (3) worms that construct permanent deep vertical burrows which they use to visit the surface to obtain plant material for food (called Anecic (meaning "reaching up")), e.g. Lumbricus terrestris.
The selection of the correct earthworm species for particular vermiculture application is important. The earthworm species (or composting worms) most often used is Eisenia fetida (Savigny) is the most commonly used earthworm species with high rates of consumption, digestion, and assimilation of organic matter; tolerance to a wide range of environmental factors, show good potential for vermicomposting. Eisenia fetida (Savigny) is epigeic species of earthworm, and also known as the “compost worm”, “manure worm”, “redworm”, and “red wiggler” (Sangwan, 2008).
Select suitable bedding and feed materials
Materials that provide the earthworm with a relative stable habitat, the materials must have the following characteristics, including (1) High absorbency: earworms breathe though their skin, so the bedding must be able to absorb and retain water fairly well if the earthworms are to thrive; (2) Good bulking potential: If the material is too dense to begin with, or packs too tightly, then the flow or air is reduced or eliminated. Worms require oxygen to live, just as we do. And (3) Low protein and/or nitrogen content (high C/N): High protein/N levels can result in rapid degradation and its associated heating, creating inhospitable, often fatal, conditions. In general, shredded paper, cardboard, horse manure, peat moss, corn silage, or paper fiber sludge makes an excellent bedding (Georg, 2004).
In the general rule-of-thumb, earthworms are able to consume the food for 1/2 of their body weight per day under ideal conditions. They will eat almost anything organic (that is of plant or animal origin), but they definitely prefer some food to others. The characteristics of food commonly used are:
Of organic origin:
Manures are the most commonly used worm feedstock, they are nutritious, and produce excellent vermicomposts. Dairy and beef manures are generally considered the best natural food for Eisenia (Gaddie and Douglas, 1975). However, they also have some disadvantages, such as weed seed make pre-composting necessary for cattle manure; high protein contents can be dangerous to earthworms due to ammonia toxicity, so pre-composting is necessary for poultry manure. Hog manure are usually in liquid form, therefore must be dewatered or used in large quantities of highly absorbent bedding. Meat and high-fat wastes can create anaerobic conditions and odors, attract pests, so should not be included without pre-composting.
Of plant origin:
Grains that feed mixtures for animals are excellent, they have balanced nutrition, easy to handle and no odor, but more expensive to use than most feeds, in addition, their water content usually are low, some large seeds are hard to digest and slow to break down. Fresh food scraps (e.g., peels, other food preparation wastes) have excellent nutrition, good moisture content, however, they are extremely variable, high N can result in overheating,
Some foods that should be avoided to be used, because they will harm earthworm growth , or attract animals and pests , including (1) anything containing meat, oil, fat, or grease, (2) diseased plant materials, (3) sawdust or chips from pressure-treated wood, (4) dog or cat feces , (5) weeds that go to seeds and (6) dairy products. Lin (2015) indicated rice bran was better in enhancing earthworms’ growth and reproduction than pig manure and watermelon rind. Although vermicompost are derived from lower nutrient contents, but they have better growth and reproduction and have lower heavy metal contents than that of pig manure, so rice bran is a better food source for earthworm growth and vermicompost production compared to the other two organic wastes.
Provide the right environmental factors
(1) Moisture content
There are strong relationships between the moisture content of organic wastes and the growth rate of earthworms. In general, earthworms can survive in moisture ranging between 50% and 90%, but grow more rapidly at 80 - 90 % in organic wastes.
Earthworms lack specialized respiratory organs, and O2 and CO2 diffuse through their body wall. Therefore, earthworms are very sensitive to anaerobic condition. They operate best when ventilation is good and the materials in which they are living in is relatively porous and well aerated. In fact, they help themselves in this area by aerating their bedding through their movement.
The most common earthworm used in vermicomposting system, such as Eisenia fedtide, Eisenia Andrei, feed most rapidly at temperature of 15oC – 25oC, They can survive at 10 oC. Their growth was reduced at 30 oC and death occurred at 35 oC. The best growth and cocoon production for E. fedtide was found was shown to occur at temperature of 20oC to 25oC.
Most epigeic earthworms can survive in a pH ranging between 5 and 9 (Edwards, 1998). In general, the pH of earthworm beds tends to drop over time. If the food source or bedding is acidic than the pH of the beds can drop well below 7. This can be a problem in terms of the development of pests such as mites. The pH can be adjusted upwards by adding calcium carbonate.
(5) Ammonia and salt content
Earthworms are very sensitive to NH3 and salts, preferring NH3 and salts of the wastes are < 1 mg/g and < 0.5 %, respectively(Guna adi et al., 2002). Many types of manure have high soluble salt contents (up to 8 %), when the manure is used as a feed, because the material is usually applied on top, where the worms can avoid it until the salts are leached out over time by watering or precipitation.
(6) Other toxic components:
Some feeds may have potentially toxic components for earthworm growth, such as urine, de-worming medicine, detergent cleansers, industrial chemicals, pesticides, tannins, these feed should avoid to be used.
Vermicompost teas are defined as water extracts leached from vermicomposted materials. Vermicompost teas are generally produced by mixing vermicompost with Cl-free water and incubating for a defined time, either actively aerating (ernated compost tea, ACT) or not (Nonaerated compost tea, NCT). Vermicompost tea is used as a foliar and soil application to plants.
Field studies have shown the benefits of adding compost teas to crops due to the adding of organic matter, increased nutrient availability and increased microbial activity (Gómez-Brandón et al., 2015). They have also been shown to have an effect on suppressing plant pathogens.( Santos, et al., 2011). Vermicompost tea is a well-balanced and nutrient-rich fertilizer and can be used on variable plants to increase growth, blooms, and yields. The trick to making vermicompost tea is using well-aged vermicompost doesn’t contain any dangerous pathogens, and using a pump to aerate the tea as it brews. Therefore, the beneficial microorganisms in the soil are able to thrive in the tea, and this makes for healthier plants.
THE APPLICATION OF VERMICOMPOSTS AND VERMICOMPOST TEAS
ON THE GROWTH AND ANTIOXIANT ACTIVITY OF LETTUCE
The application effects of vermicomposts and vermicompost teas on soil quality, crops growth, nutrient uptake and soil fertility may be varied with the characteristics of food fed. Vermicomposted rice bran (VRM) and vermicomposted fruit residue (VFM) were produced using Eisenia fetida fed with rice bran and fruit residue for 8 week vermicomposting, respectively. The brewing method was used to produce vermicompost teas with adding 5% molasses, , and 30 g/L sesame meal, 30 g/L fish meal and 10 g/L plant ash , vermicompost and water was at the rate of 1:10 (W / V), then aerated continuously for three days. Then a pot lettuce experiment was conducted to evaluate the effects of (1) Check , (2) chemical fertilization (CF), (3) composted animal manual (CAM), (4) vermicomposted rice bran (VRM), (5) vermicomposted fruit residue (VFM), (6) Mix. 1 : 2/3 vermicomposted fruit residue (VFM) + 1/3 vermicomposted fruit residue tea (VFMT) and (7) Mix.2: 2/3 vermicomposted rice bran (VRM) + 1/3 vermicomposted rice bran tea (VRMT) and on the growth, nutrient uptake and antioxidant activity of lettuce and soil fertility. VFM and VRM were applied on the soil, and VFMT and VRMT were applied on the leaf and the amount of each fertilizer treatment was calculated based on the N recommendation of lettuce (N: 120 kg/ha). Besides N, Chemical fertilizer treatment also applied 50 kg/ha P2O5 and 90 kg/kg K2O (Tsai 2016).
Table 1. Properties of vermicomposted fruit residue(VFM), vermicomposted rice brain (VRM) and composted cattle manure (CAM)
The results showed that pH and EC values , the contents of main ingredients (N, P2O5, K20), harmful ingredients(Cd, Cr, Cu, Zi, Ni,Hg, Pb ,As), and organic carbon of vermicomposted fruit residue (VFM), vermicomposted rice bran (VRM) (Table 1) and rice bran vermicompost tea (VRMT) and fruit residues vermicompost tea (VFMT ) (Table 2) all complied with the standard of organic fertilizers and liquid organic fertilizers issued by the Council of Agriculture (COA) of Taiwan, respectively. Therefore, they can be defined as high quality fertilizers.
Table 2. Properties of vermicompost teas produced
* VFMT: Vermicompost tea with fruit residue. VRMT : Vermicompost tea with rice bran.
# EC: Electrical conductivity
Growth and nutrient uptake
Fig. 1 showed that all treatments except CF treatment, increased the dry weight of lettuce, the highest effects were found in Mix. 1 and Mix. 2 that vermicompost applied on the soil and vermicompost tea was applied on the leaf. The dry weight of lettuce of CAM, VFM, and VRM treatments were significantly higher than that of CF treatment, but there was no significant difference among them. Use of vermicompost has been found effective for improving soil aggregation, structure, and soil fertility, increasing soil microbial population and enzymes, improving moisture-holding capacity of soil, increasing cation exchange capacity, and crop yield (Tejada et al., 2008). The results of Vivas’s research indicated that vermicompost has plant growth hormones, higher level of soil enzymes, such as dehydrogenase , and other enzyme activities, greater microbial population than that of conventional compost. Dehydrogenase, urease, protease, and cellulose activity in soil also improved by vermicompost application (Ronero et al., 2010).
Fig. 1. The amounts of phenolic compounds and flavonoids of lettuce in each treatment
The effects of different fertilizers application on the N, P and P uptake by lettuce werer recorded in Table 3. Data showed that compared to the control treatment, all the fertilizer treatments except CF were significantly increased the nutrient uptake of N, P and K, the highest uptake of N was found in the Mix.1 and Mix.2 treatments. However, statistically the differences among the treatments of CAM, VFM, VRM, Mix.1 and Mix.2, was not significant. Nutrient uptake precedes dry matter accumulation because nutrients are required for plant growth and hence dry matter accumulation. Nutrients can be absorbed by plant roots and leaves, mainly uptake by plant root. It was demonstrated that leaf‐supplied nutrients were accumulated in the plant biomass and even stimulated root nutrient uptake,maybe it was the main reason for better growth and nutrient uptake of lettuce in the treatment of Mix. 1 and Mix.2.
Table 3. The uptake of total N and P by lettuce in each treatment applied with different fertilizer
Antioxidants are capable of scavenging free radicals, which can oxidize major biological macromolecules (DNA, protein and lipid) in cells and tissues. If the oxidative damage is beyond the capacity of natural repair mechanisms of the cell, it may result in human cancer (Franco et al., 2008). It is suggested that eating the heantioxidants rich foods may prevent cancer, vitamins and certain ptytochemical antioxidants (such as flavnoids and carotenoids are effective against the proliferation of human cancer cells ( Wang et al., 2011) . Caldwwell (2003) had detected significant levels of antioxidants activities and phenolic components in lettuce . The content of flavonoids and phenolic acid in lettuce is sensitive to environmental condition and antioxidant activity of lettuce (Liu et al., 2007).
As presented in Figure 2, the amounts of phenolic compounds and flavnoids of lettuce were significantly increased by fertilizer application, maximum amount were observed in the Mix. 1, Mix.2 and VFM treatments, followed by VRM and CAM treatment, and then CF treatment. The DPPH radical scavenging ability of organic fertilizers was higher than that of CF treatment and those treatments using vermicomposts and vermicompost tea all had higher DPPH radical scavenging ability than conventional compost and chemical fertilizer (Fig. 2). The results confirm that organic fertilizer, especial for the combination treatment of vermicompost and compost tea, can be beneficial in producing antioxidants and improving antioxidant activity of lettuce.
Fig. 2. The amounts of phenolic compounds and flavonoids of lettuce in each treatment
Organic matter in soil serves as a reservoir (pool) of crop nutrients and with general functions of improving soil (physical, chemical and biological) properties to favor the crop tillage and management, thus, its content in soil could be regarded as an ideal index of fertility level (Ellet et al., 1987). Table 3 showed that all treatments included compost or vermicompost had higher organic matter content of soil than those of CK and CF treatment due to more organic matter provide by application of organic fertilizers. VFM (OM: 78%) and VRM (OM: 75%) contained higher amount of OM than that of CAM(OM: 53%), but the OM content of the soil was lower than that of CAM treatment. It suggested that the organic matter in vermicompost is more easily decomposed than cconventional compost after adding on to soil. Organic fertilizers application also significantly increased Bray-1 content of soil than those of CF and CK treatments, the highest content was noted in the treatment of CAM (P2O5: 4.2%), followed by VAM (P2O5: 5.0%) and VFM (P2O5: 5.0%). It indicated the increase of Bray-1 content of soil was not only determined by the P2O5 content of the organic fertilizers added.
Use of compost can be expected to enhance the availability of soil P and promote the efficiency of P fertilizers, due to its decrease effect of P adsorption. Mechanisms to explain decrease effect of compost on P adsorption are multiple and suggested as follows: (1) complex of Fe, Al or Ca with humic or organic acid formed to decrease the opportunity of P adsorption.（Barrow, 1989）(2) adsorption sites preoccupied by organic P.（Chen, 1995）(3) adsorption sites preoccupied by inorganic P ions dissolved from organic fertilizer or released from the mineralization of organic P fractions.（Chen, 1995）and (4) pH fluctuation lead to the variation of surface charge on soil colloid.
The quality of vermicomposts is determined partly by the degree of earthworm activity and the conditions they have been exposed to, but mainly by the composition of the organic wastes used. The results of pot experiment showed that all treatments with fertilizer adding, increased the yield and nutrient uptake by lettuce, but the effects were relatively low for CF treatment. The highest effects were found in the treatment of Mix. 1 and Mix. 2 treatments t. The total amount of antioxidants of all treatments were significantly increased with yield, vermicompost application had the ability in antioxidant ability improvement. The DPPH radical scavenging ability of VFM and VRM were higher than those of CAM and CF treatments, however, the best effect were found in the treatments of Mix. 1 and Mix. 2. that combined use of vermicompost that applied on the soil and vermicompost tea that applied on the leaf. It suggested that nutrients supplied from roots and leaves simultaneously, will be a smart fertilization for vermicompost in improving plant growth, nutrient uptake and antioxidant activity of plant.
Table 4. Soil pH, organic matter (O.M.) and Bray-1 P content in each treatment applied with different fertilizers after lettuce harvesting
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