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Chapter 10

Preparing Compost and Silage from Water Hyacinth

Robert N. Muzira, Alice Amoding and Mateete A. Bekunda

Water hyacinth, Eichhornia crassipes (Mart), is an aquatic plant from Tropical America belonging to the family Pontederiaceae. The mature plant consists of long fibrous roots, rhizomes, buoyant petioles, stolons, leaves, inflorescence and fruit clusters. The inflorescence bears between 6 and 120 lily-like violet and yellow flowers. The fruit is a capsule, containing up to 450 seeds. Water hyacinth is a problem in water bodies because of its dense strands and rapid proliferation. It is very efficient in utilizing aquatic nutrients and solar energy for profuse biomass production (Amoding et al., 1999).

Depending on the time of the year and location, the plants double in number and biomass every 6 to 15 days. Between 400 and 1700 tonnes fresh weight are produced per hectare per year. Given that the dry weight is about 5-7% of fresh weight, one hectare yields between 20 and 120 tons of dry water hyacinth per year, containing nitrogen (N), phosphorus (P) and potassium (K) as well as other plant nutrients. It makes sound economic sense to utilize the water hyacinth as an organic input to soils. Water hyacinth waste provides mulch that assists in both water retention and weed suppression.  When composted with a variety of materials such as animal manure, phosphate rock and wood ash, its nitrogen content increases making it more suitable for the production of higher-value crops or as an ingredient for potting mixtures (Table 1).

Compost is a mixture of the remnants of degraded plant material and the by-products of the degrading organisms. It is produced through a process referred to as “composting”.  Several factors influence this process and its rate.  Substrate size is important because smaller plant material degrades more rapidly due to its higher surface area. Initially, temperature affects the types of organisms that colonize the compost pile and the rate of their metabolism but later, heat released by microbial decomposition determines the compost’s peak temperature. Composting proceeds more rapidly during warmer months and slower during the cooler months.  The placement and dimensions of the compost may increase decomposition rates due to better aeration and moisture conservation.  Alternatively, poorly drained or drier conditions slow the rate of compost production.

Table 1. Changes in the chemical characteristics of composting water hyacinth.

The following procedure describes a pit composting technique that is appropriate for water hyacinth and other course-textured materials. Pit composting generally requires more time than raised (piled) composts but it requires less initial investment and better conserves moisture.

Preparing Pit Compost

1. Prepare a pit 1.5 m long  x 1 m wide  x 1 m deep and line the sides and bottom with plastic sheeting.

2. Obtain 5 to 10 t of fresh water hyacinth plants, place them into the pit, spread 10 to 20 kg of cattle manure across the top as a biological activator and cover the pit with plastic sheeting.

3. After 1 month, uncover the pit and mix with a pitchfork. By this time, plants are light brown, leaves are decomposing and stems and roots are more-or-less intact

4. After another month, uncover and mix with a pitchfork again. Material is now dark brown, shoots are decomposed and the corms and roots are beginning to fragment. Replace plastic cover.

5. After one more month, uncover and remove finished compost from the pit, spread, break apart large "clods" and dry.

6. After drying, the dark coloured compost is ready for application to soil.

Fortifying Compost with Rock Phosphate

1.       Retrieve well-composted water hyacinth material from the pit

2.       Spread the material on a plastic sheet or concrete floor to drain out excess water

3.       When it is still moist, pass the compost through a 5 or 10 mm screen

4.       Put the screened material on a plastic sheet and mix with 5% ground phosphate rock

5.       For larger volumes use a cement mixer or oil drum to mix the material

6.       Pack the mixed product in convenient bags, for example 3, 5 or 10 kg bags.

7.       Store secured bags of the compost in a dry place until the time of application

Preparing Potting Mixtures from Water Hyacinth Compost

1. Partially dry the water hyacinth compost

2. Separately pass the compost, coarse sand and charcoal granules through a 5 mm screen

3. Put the screened compost, sand and charcoal on plastic sheet; and mix with powdered phosphate rock and crushed bone in the ratio of 20:10:10:1:1

4. For large volumes use a cement mixer or oil drum to mix

5. Pack the mixed product in storage bags

Using Compost and Potting Mixtures

Remember that compost is great for improving the condition of your soil. With compost you will get better crops and healthier plants. Now is the time to start using this wonderful material.

• In the garden. Spread the compost on the soil about 3 to 5 cm thick and incorporate it into the soil before planting.

• To existing garden beds. Place the compost around the existing plants as top dressing mulch. If you wish, dig the compost into the soil being careful to avoid disturbing plant roots.

• As a potting mixture. You can make great potting mixes for indoor and outdoor plants using compost. Try mixing compost, soil, sand and manure for a rich well-drained potting mixture (as described above).

• Remember your friends.  Whenever you have too much compost, give some away to friends.

Preparing Silage

Scientists in the Faculty of Agriculture at Makerere University in Uganda have developed a simple method to prepare nutritious feed for livestock from water hyacinth that promises to commercialize this use. Silage is made by combining wilted water hyacinth with 10% maize bran and allowing the mixture to ferment for 20 days. Silage is produced by the activities of naturally-occurring bacteria that convert some of the plant sugars into organic acids that preserve nutritional qualities. The finished product is golden brown in colour, sweet smelling, readily acceptable to cattle and may be stored for long periods without loss of quality. The following procedure produces silage useful as a feed supplement (Lindsey and Hirt, 1999; Woomer et al., 1999).

1. Recover. Fresh water hyacinth plants are recovered from a clean water body and the roots removed and dried for use as an ingredient in potting soil. Do not use water hyacinth taken from polluted waters as it may contain toxic heavy metals.

2. Chop dry and mix. The shoots, consisting of leaves, petioles (stalks) and rhizome (base), are chopped into large pieces and air dried to about 80% moisture. Drying a large pile requires about two days and periodic mixing until the leaves and stalks are just beginning to wilt. Add 7.5 kg of maize bran to 42.5 kg of water hyacinth and mix in a large tray or on a rolling tarpaulin until the maize bran uniformly coats the chopped water hyacinth. This mixture may be prepared by combining 11 parts water hyacinth to 1 part maize bran. Maize bran will not adhere to the chopped water hyacinth if it is too dry. If this problem occurs, sprinkle 2 litres of water on the chopped water hyacinth and maize bran and re-mix the materials.

   Figure 2. Water hyacinth utilization in Uganda. Fresh water hyacinth (upper left) is collected and transported (lower left) for processing into silage (upper right) and compost (lower right).

3. Bag and store. Tightly pack the mixture into a large, medium gauge, air-tight plastic bag and close bag with string or wire. Squeeze out any remaining air when tying the plastic bag. Stack 3 to 4 bags in an upside-down position. This minimizes the entry of air from any tears in the plastic bags. Place the bags away from the sun or cover with a non-transparent sheet. It is normal for the bags to feel warm to the touch after three days or so. The contents will turn from green to olive to brown during the first week.

4. Feed. The silage is ready for use after 14 to 20 days and can be stored for several months without loss of quality. Very little weight loss occurs during silage fermentation or storage. Use silage as a feed supplement, not a complete ration. Poultry and ducklings perform poorly with this feed but cattle, goats, pigs and rabbits are well suited to it.

The silage is approximately 20% dry matter. The dry matter contains 13% crude protein, 20% acid detergent fibre, 0.4% calcium and 0.8% phosphorus. Silage may be prepared by substituting molasses for maize brain but the resulting feed is lower in dry matter and crude protein. The silage resulting without addition of either maize bran or molasses has poor nutritional value and storage characteristics. The scientists at Makerere are currently investigating the use of sweet potato vines and urea as additives as well as preparing the silage on a larger scale in brick-lined pits. Preparing compost or silage from water hyacinth offers many advantages (Woomer et al., 1998). It provides incentive for communities to recover water hyacinth from the shoreline, eliminates the problem of waste disposal and reduces the need of growing or collecting other green manures and fodders.

References

Amoding, A., Muzira, N.R., Bekunda, M.A and Woomer, P.L. 1999. Bioproductivity and decomposition of water hyacinth in Uganda. African Crop Science Journal 7:433-439.

Lindsey, K. and Hirt, H.M. 1999. Use Water Hyacinth! Anamed, Winnenden, Germany. 114 pp.

Woomer, P.L., Bekunda, M.A., Karanja, N.K, Moorehouse, T. and Okalebo, J.R. 1998. Agricultural resource management by smallhold farmers in East Africa. Nature and Resources 34(4):22-33.

Woomer, P.L., Muzira, R., Bwamiki, D., Mutetikka, D., Amoding, A. and Bekunda, M.A. 1999. Biological management of water hyacinth waste in Uganda. Biological Agriculture and Horticulture 17:181-196.

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