Composting is a biological process in which microorganisms decompose organic matter and lower the carbon-nitrogen ratio of the substrate. It is generally prepared from organic waste material such as crop residue, household waste etc.

Methods of composting

The available residues in the farm are collected and stored till they form sufficient mass for compost making. A trench of suitable size, say, 4-6 m long, 2-3 m broad and 1-1.5 m deep is dug, the accumulated residues is well mixed, and spread in a layer of 30 cm in thickness, along the length of the trench. This layer is well moistened by sprinkling cowdung slurry and water over it. A second layer of identical thickness of the mixed residues is then spread over the first layer. The process is repeated till the heap rises to a height of 45 cm to 60 cm above ground level. The top is then covered with a thin layer of soil. After three months of decomposition, the mass is taken out of the trench and formed into a conical heap above the ground, moistened with water if necessary, and covered with soil. After one or two months, the manure will be ready for application in the field.

Vermicompost

Vermitechnology is a process by which all types of biodegradable wastes such as farm wastes, kitchen wastes, market wastes, biowastes of agro-based industries, livestock wastes etc. are converted to nutrient rich vermicompost by using earthworms as biological agents. Vermicompost contains major and minor nutrients in plant available forms as well as enzymes, vitamins and plant growth hormones.

Species suitable: Eudrillus eugineae has been identified as the most ideal species of earthworm for vermitechnology under Kerala conditions.

Vermicomposting of farm wastes

Pits of size 2.5 m length, 1 m breadth and 0.3 m depth are taken in thatched sheds with sides left open. The bottom and sides of the pit are made hard by compacting with a wooden mallet. At the bottom of the pit, a layer of coconut husk is spread with the concave side up to ensure drainage of excess water and also for proper aeration. The husk is moistened and above this, biowaste mixed with cowdung in the ratio of 8:1 is spread up to a height of 30 cm above the ground level and water is sprinkled daily. After the partial decomposition of wastes for 7 to 10 days, the worms are introduced @ 500 to 1000 numbers per pit. The pit is covered with coconut fronds. Moisture is maintained at 40 to 50 per cent. After around 60 to 75 days, when the compost is ready, it is removed from the pit along with the worms and heaped in shade. The worms will move to bottom of the heap. After one or two days the compost from the top of the heap is removed. The undecomposed residues and worms are returned to the pit for further composting as described above. The vermicompost produced has an average nutrient status of 1.5 per cent N, 0.4 per cent P₂O₅ and 1.8 per cent K₂O with pH ranging from 7.0 to 8.0. The nutrient level will vary with the type of material used for composting.

Precautions

1. The composting area should be provided with sufficient shade to protect it from direct sunlight.

2. Adequate moisture level should be maintained by sprinkling water whenever necessary.

3. Preventive measures should be adopted to ward off predatory birds, ants, rats, etc.

Vermicomposting of coconut leaves

Weathered coconut leaves can be converted into good quality vermicompost in a period of three months with the help of earthworm, Eudrillus sp. On an average, 6-8 tonnes of leaves will yield 4-5 tonnes of vermicompost with about 1.2, 0.1 and 0.5 per cent N, P₂O₅ and K₂O respectively.

Vermicomposting of household wastes
A wooden box of 45 cm x 30 cm x 45 cm or an earthen/plastic container with broad base and drainage holes may be selected. A plastic sheet with small holes may be placed at the bottom of the box / container. A layer of soil of 3 cm depth and a layer of coconut fibre of 5 cm depth may be added above it for draining of excess moisture. A thin layer of compost and worms may be added above it. About 250 worms are sufficient for the box. Vegetable wastes of each day can be spread in layer over the coconut husk fibre. Top of the box may be covered with a piece of sac to provide dim light inside the box. When the box is full, it can be kept without disturbance for a week. When the compost is ready, the box can be kept outside for 2-3 hours so that the worms come down to the lower fibre layer. Compost from the top, may be removed, dried and sieved. The vermicompost produced has an average nutrient status of 1.8 per cent N, 1.9 per cent P₂O₅ and 1.6 per cent K₂O, but composition will vary with the substrate used.

Mass multiplication of earthworms

Earthworms can be multiplied in 1:1 mixture of cowdung and decaying leaves in a cement tank or wooden box or plastic bucket with proper drainage facilities. The nucleus culture of earthworms is to be introduced into the above mixture at the rate of 50 numbers per 10 kg of organic wastes and properly mulched with dried grass, straw or wet gunny bag. The unit should be kept in shade. Sufficient moisture level should be maintained by occasional sprinkling of water. Within 1-2 months, the earthworms multiply 300 times, which can be used for largescale vermicomposting.

Preparation of vermiwash

Method 1

The system consists of a plastic basin having a capacity of 20 litres, a plastic perforated wastepaper basket and a PVC pipe of 5 cm diameter and 30 cm length. The waste paper basket is covered with a nylon net and placed at the centre of the basin upside down. A hole is made at the bottom of the waste paper basket so that a PVC pipe of 5 cm diameter can be placed into the basin through the hole in such a way that one end of it touches the basin. The PVC pipe is perforated so that the leachate from the basin seeps through the wastepaper basket and collects in the PVC pipe, which can be siphoned out by a kerosene pump. The basin outside the wastepaper basket, is lined with a layer of brick pieces at the bottom and a 2-3 cm thick layer of coconut fibre of 2-3 cm placed above it. After moistening this, 2 kg worms (about 2000) are introduced into it and 4 kg kitchen waste is spread over it. After one week, the kitchen waste turns into a black well decomposed compost. Two litres of water is sprinkled over the compost containing worms. After 24 hours, the leachate collected in the PVC pipe is removed by siphoning. The collected leachate is called vermiwash, which is actually an extract of compost containing worms. This is used for soil application and foliar spray in different crops. Vermiwash is honey-brown in colour with a pH of 8.5 and N, P₂O₅ and K₂O content 200, 70 and 1000 ppm respectively. For large scale collection of vermiwash, a cement tank of size 80 cm x 80 cm x 80 cm with a side tap is constructed. A layer of small brick pieces or gravel is placed at the bottom of the tank. Above it a layer of fibre of 3-4 cm thickness in placed. A definite quantity of biowaste (4 kg) is added to the system along with 2 kg of earthworms. After two weeks, the entire mass of biowaste will turn to brownish black compost. It is sprinkled with 2 litres of water. Vermiwash is collected through the side tap after 24 hours. Biowaste can again be added to the system and the process repeated.

Method 2

This is a simple and economical technique to collect vermiwash. The system consists of an earthen pot of 10 kg capacity with a hole at the bottom, which is filled with pieces of stone up to a height of 10 cm from the bottom. A plastic net is spread over this. Then a thick layer of coir fibre along with humus containing 1500-2000 worms of Eudrillus euginae or Isenia foetidae is added to the pot. The hole situated at the bottom of the pot is fixed with a water tap through which vermiwash is collected. The kitchen waste of each day is added to the container. The composting process is allowed to continue for a week or more till brownish black mass of compost is obtained. Occasionally, two or three tablespoons of fresh cowdung slurry is poured on the humus as feed for the worms. After the formation of compost, the entire mass is soaked with two litres of water. After 24 hours, about 1.5 litre of vermiwash can be collected. This process can be continued for one or two weeks till the brown colour of wash disappears. The less enriched compost that remains in the pot can be collected and used as fertilizer. Later, the pot can be emptied and set up again to continue the process.

The vermi wash, either alone or in combination with botanical pesticides can be used for pest management in kitchen gardens.

Recommendation for crops

When vermicompost is applied as organic manure instead of FYM, the quantity of in-organic fertilizers can be reduced to about half the recommended dose.

Coirpith composting

Coirpith, is produced in large quantities as waste material of the coir industry. Every year, approximately 2.5 lakh tonnes of coirpith accumulate in Kerala as waste. Coirpith has wide C:N ratio and its lignin rich nature does not permit natural composting process as in other agricultural wastes. Mushrooms belonging to the genus Pleurotus have the capacity to degrade part of the cellulose and lignin present in coirpith by production of enzymes such as., cellulases and lactases, bringing down the C:N ratio as well as lignin content.

Method of composting

Materials required: Coirpith 1 tonne, urea 5 kg, mushroom (Pleurotus) spawn 1.5 kg.

A shaded place of 5 m x 3 m dimension may be selected and levelled after removing weeds. 100 kg coirpith may be spread uniformly. Spread 300 g (one bottle or cover) of Pleurotus spawn on this and cover with a second layer of 100 kg coirpith. On the surface of the second layer, spread 1 kg urea uniformly. Repeat this sandwiching process of one layer of coirpith with spawn followed by another layer of coirpith with urea up to 1 m height. Sprinkle water if necessary to keep the heap moist. Allow the heap to decompose for one month.

The coirpith is converted into good manure after 30-40 days and the lignin content is reduced from 30 per cent to 40 per cent. Another significant change is the lowering down of C: N ratio from

112:1 to 24:1.

The use of biofertilizers is important while practising integrated plant nutrient management as well as organic farming. Some of the commonly used biofertilizers in Kerala are as follows.

1. Rhizobium (Bradyrhizobium and Azorhizobium)

It induces better root nodulation and stem nodulation in inoculated plants and thereby brings down the requirement of nitrogen fertilizer for the cultivation of pulses, oil seeds and legume green manures. Commercially it is available as carrier based inoculum. Method of application is seed treatment.

2. Azotobacter
Suitable for upland crops like vegetables, tapioca, plantation and orchard crops. It is available as carrier-based inoculum. It fixes about 15-20 kg of N per ha under ideal upland conditions and thereby reduces the requirement of nitrogen fertilizers by 10-20 per cent. Methods of application are seed treatment, seedling dip and direct soil application.

3. Azospirillum

It is suitable for both upland and wetland conditions and is available as carrier-based inoculum. It fixes about 20-25 kg N per ha under ideal conditions, thereby effecting a reduction of 25 per cent in the quantity of N fertilizers required. Treatment with Azospirillum also induces better root formation in inoculated plants. Hence this biofertilizer is also recommended for root induction in polybag raised seedlings of plantation and orchard crops as well as vegetables. The isolates of Azospirillum brasilense strains AZR 15 and AZR 37 from Kuttanad soils are highly effective for rice, vegetables and nursery plants.

Methods of application

Seed treatment: For treating 5-10 kg seeds, 500 g culture is required. Moisten the seeds by sprinkling water or rice-gruel water. Take 500 g culture in a plastic tray/basin, add moistened seeds, mix well and dry in shade for 30 minutes. This may be sown immediately.

Seedling root dip (for transplanted crops): Slurry of the culture is prepared by mixing 500 g culture with 50 ml of water and the roots are dipped in the slurry for 15-20 minutes before transplanting.

Soil application: Mix the culture with FYM or compost in the ratio 1:25 and apply directly in the soil.

Inoculation for paddy: Mix 2 kg of culture in 60 litres of water and soak the seeds required for 1 ha (60 kg) for 24 hours before sowing. At the time of transplanting, dip the roots of seedlings for 15-20 minutes in the culture slurry prepared by mixing 2 kg inoculum with 40 litres of water. This slurry can be used for treating seedlings required for 1 ha. Another 2 kg culture may be applied in the field along with FYM or compost.

4. Blue green algae (BGA)

Mainly recommended for wetland rice cultivation. It is available as carrier-based inoculum and it fixes about 25-30 kg N per ha under ideal conditions. However, the use of this biofertilizer is not feasible in acidic soils with pH below 6.0.

Method of application

Broadcasting in the rice fields at the rate of 10 kg ha-1 one week after transplanting.

5. Azolla

It is suitable for wetland rice cultivation. The required quantity of azolla will have to be raised in the farmers field itself. Fixes about 25 to 30 kg N per ha.

Method of application: Apply fresh

azolla at the rate of 10 t ha-1 at the time of ploughing.

6. Phosphate solubilising bacteria and fungi

Recommended mainly for upland crops raised in neutral and slightly alkaline soils. Available as carrier-based inoculum. Enables the efficient utilization of cheaper sources of phosphatic fertilizers such as rock phosphate by the crop plants.

Method of application: Seed treatment and direct application.

7. Vesicular/Arbuscular mycorrhiza (VAM/AMF)

Vesicular arbuscular mycorrhiza is mostly recommended for upland crops, especially for raising container and tissue culture plantlets and transplanted crops. It mainly improves the uptake of available P by inoculated plants. There is also an enhanced absorption of water and other nutrients such as N and K and certain micronutrients. Mycorrhiza inoculation can improve the survival and establishment of tissue culture plantlets under field conditions as well as induce better resistance against certain soil borne plant pathogens. It is commercially available as granular inoculum consisting of infected roots and soil with mycorrhizal spores. It is given as soil application.

VAM fungus Glomus microcarpum var. microcarpum is suitable for tropical tuber crops. The inoculation can be done by placing inoculum (3-5 g/sett) beneath the sett before planting. The rate of spore load in the inoculum should be to the tune of 50 to 400 spores per 100 g soil medium. Method of application is the rooted infected cutting technique.

Application techniques of biofertilizers

1. Seed treatment

Five hundred grams of commercially available inoculum will be required for treatment of seeds for one hectare area. For this, thick slurry of the carrier-based inoculum is initially prepared by mixing 500 g of the inoculum in 1.25 litres of water. The stickiness of the biofertilizer on seed surface can be significantly improved by using 10 per cent jagerry solution or 5 per cent sugar solution supplemented with 40 per cent boiled and cooled gum arabic solution or rice-gruel water. The required quantity of seed material is then gently mixed with this slurry without damaging the seed coat. The treated seeds are spread evenly over a gunny bag and dried in shade and sown immediately in moist soil. The treated seeds should never be exposed to direct sunlight for a long period of time since the UV rays of solar radiation will reduce the population of inoculated bacteria on seed surface significantly.

2. Seedling treatment

This method is mainly recommended for transplanted crops. The roots of seedlings to be transplanted are dipped in water slurry of the biofertilizer (500 g in 2.5 litres of water) for 20 minutes, prior to transplanting.

3. Soil application
Soil application is generally recom-mended for all types of biofertilizers except Rhizobium, Bradyrhizobium and Azorhizobium. The method is to apply the biofertilizer after mixing with dried FYM,

compost or vermicompost at the rate of 1:25. For crops of six-months duration, the recommended dose is 1-2 kg ha^-1. This can be increased to 2-4 kg ha^-1for crops of more than six months duration. For perennial crops, 10 to 25 g of the biofertilizer is to be applied in the root zone during the first year and 25 to 50 g during subsequent years. This can be done at the time of sowing, transplanting or during intercultivation.

Factors influencing the efficient use of biofertilizers in Kerala

1. Use adequate quantity of organic manure (as per the recommendation for each crop) along with biofertilizer application. This is essential to ensure better survival, growth and activity of the introduced microbial inoculum in acidic soils.

2. Liming is essential if the soil pH is below 6.0. In moderately acidic soils, the application of lime at the rate of 250 kg ha^-1 is recommended along with biofertilizer treatment.

3. Irrigation is essential during summer months after biofertilizer application to ensure the survival of the introduced microbial inoculum in the soil.

4. Since N biofertilizers can supplement only a part of the nitrogen requirement of the inoculated plant, low dose of nitrogen and full doses of phosphorus and potassium as per the recommendation may be applied. This is essential to ensure better plant growth and yield. Similarly, in the case of P biofertilizers, the full doses of nitrogen and potassium should be applied. However, there should be a gap of at least one week between application of biofertilizer and chemical fertilizer.

5. Use only biofertilizers, which are manufactured as per the quality parameters prescribed by the Bureau of Indian Standards. In the case of bacterial biofertilizers, the prescribed standard is that in the final product, the population of the desired bacterium should not be less than ten million per gram of the carrier material and there should not be any contamination with other microorganisms when examined at 1:100000 dilution. Further, it should have a shelf life of at least six months.

6. The commercially available biofertilizer should always be used before the expiry date marked on the culture packet.

7. Top dressing with superphosphate at the rate of 25 kg ha^-1 10 days after inoculation of BGA will enhance its growth under field conditions.

8. Since the occurrence of green algae in rice field can affect the normal growth and proliferation of BGA, the population of green algae should be controlled initially by applying copper sulphate at the rate of 4 kg ha^-1.

9. In moderately acidic soils of pH around 6.5, root nodulation by Rhizobium and Bradyrhizobium can be improved by pelleting with finely powdered calcium carbonate. (See recommendation under cowpea)

10. Application of P₂O₅ at the rate of 1 kg ha^-1 is recommended once in 4 days in P₂O₅ deficient soils to ensure good growth of azolla. The development of a reddish purple colour in azolla is a typical symptom of P₂O₅ deficiency.