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The use of the decayed tissues of unwanted plants to provide nutrients for crops is a crude but effective way of exploiting weeds and is a simpler technique than any of the other alternatives available. Aquatic plants dragged from their environment to rot on dry land have the advantage that their seeds or vegetative parts do not present any risk of competing with the crop, but this involves considerable labour (as discussed in Chapter IV on harvesting). In areas where water weeds cause the greatest difficulty labour may be relatively cheap and the inducement to use the weeds enhanced by the cost and scarcity of artificial fertilizers, yet it is not universally common for poor farmers near large areas of aquatic weeds to exploit this resource. Kamal and Little (1970) illustrate the struggle of a gardener working on the banks of the Nile ignoring the vast resources of water hyacinth nearby and available for the taking.

Clearly the best use of aquatic weeds for horticulture would be to apply themas a thick layer on the soil to suppress weeds and conserve moisture. They could be used either during a fallow or as a mulch for a growing crop. When decay had eventually reduced the effectiveness of the mulch then the residues could be incorporated into the soil to add organic matter and nutrients.

Where the crop is distant from the weed source then, if possible, the weeds should be allowed to dry on the bank in order to minimize labour and transport costs; or the weeds could be composted, and when the process had been completed the much less bulky finished product could be transported. A further alternative, discussed in some of the papers in this chapter, is to burn the dried weeds and use the ash residue which would contain most of the minerals, except N, and weigh a small fraction of the original wet weed. This is a difficult operation in other than exceptionally dry countries or seasons when complete desiccation of the plants by solar heat is possible. An advantage of this procedure is that it minimizes the risk of transporting viable portions ofany weed into regions so far uninfested.

The papers that follow discuss all these aspects of the use of aquatic plants for crop improvement.

Abdalla, A.A. and A.T. Abdel Hafeez, 1969 Some aspects of utilization of water hyacinth (Eichhornia crassipes). PANS, 15(2):204–7

The authors carried out experiments in the Sudan with the use of water hyacinth as a mulch to suppress nutsedge, Cyperus rotundus. Using plots 3 m x 3.7 m, records were made of the effect of three rates of mulching on weed suppression. The mulch was kept in position for three weeks after which tubers of thesedge were taken from each plot and the time taken to sprout, as well as the growth rate, measured. In addition, the effect on retention of moisture in the soil as a result of themulch was measured at three soil depths. The results are tabulated below:

Water hyacinth mulch tonnes/haDays to 50% tuber sproutingGrowth rate mm/daySoil moisture %
Surface 0–13 cm15 cm deep30 cm deep

The authors conclude that the use of a water hyacinth mulch can be effective in controlling Cyperus rotundus and also in substantially conserving soil moisture. (See also Hafeez, 1975.)

* Basak,M.N., 1948 Water hyacinth compost. Alipore, West Bengal Govt. Press

The author begins by discussing the burning of water hyacinth to ash for fertilizer use in Bengal. He rejects this because of the loss of valuable nitrogen and organic matter, the labour and difficulty of drying the plant, especially in wet weather, and the difficulty of storing and bagging the ash. He advocates the making of water hyacinth compost, which he says is “four times richer than farmyard manure and is less than the usual price of the latter.” He considers that where labour is cheap mechanical harvesting is unnecessary and that the value of the compost will more than pay for the cost of making it.

“Floating masses of water hyacinth were easily drifted to the edge of the embankments by towing round a piece of rope or by the help of a boat; this minimised labour and difficulty of transport. Bunches of plants were then picked up from water by hand and spread immediately (without drying) on a square (10' x 10') [3 x 3 m], rectangular or circular plot (5 feet [1.5 m] in diameter) of plain high land, uniformly and loosely into a 1-foot [0.3 m] layer; care was taken to prevent any trampling or pressing of the heap. On the water hyacinth layer was placed a thin layer (1" to 2") [2.5–5.0 cm] of undiluted cowdung, alone or mixed with a little canal mud, urine earth or prepared compost. If cowdung or urine earth was not easily available in the area, as happened when the centre was far away from habitations, the addition of the above materials also helped decomposition. Cattle dung and urine earth which act as valuable “starters” are always preferable for they not only enhance decomposition through necessary supply of suitable bacterial inoculum but enrich the final product by incorporation of additional nitrogen. A second 1-foot [0.3 m] layer of water hyacinth was similarly built up on the first with a thin layer of cowdung on it and the process repeated till the heap rose to about 6 ft [1.8 m]. The topmost layer of water hyacinth was built up in the shape of a dome and the top was plastered with cowdung and canal mud to prevent any subsequent intrusion of rain water into compost heaps.

“Previous drying of green water hyacinth and then moistening it with a slurry of cowdung and water (1:10) during the making of compost heaps were unnecessary. Instead, semi-solid cowdung was added and the surplus water sticking to plants diluted cowdung in the layer below and in course of draining away effected thorough mixing with the water hyacinth layer underneath. Another important point was the taking of over-ground heaps. It was difficult to have dry pits, particularly in the rainy season, due to high rainfall and subsoil water-table in Bengal and the compost charged pits were susceptible to holding outside water to delay decomposition and cause leaching of soluble nutrients. Heaps were comparatively free from these drawbacks and had additional advantages over pits in dispensing with the cost of digging and in facilitating draining out of surplus water and evaporation of excess moisture, which hastened decomposition.

“The heaps were left exposed to sun and air for 4 to 6 weeks, in which interval excess water was slowly lost with corresponding rise in temperature and growth of fungus; fermentation proceeded fairly rapidly and the heaps sank down to half the former level into a damp moist mass. If there was occasional rain it brought down temperature and slackened fermentation; fungus growth was scanty and sluggish. Although soft leaves and stalks were quickly fermented, the stems were a bit more resistant and after 4 to 6 weeks turned brown and partially decomposed but still retained hardness, particularly if dung was not added in the making of heaps. After the said interval the whole mass was given a complete turning, 2 or 3 sunken heaps making a new one of parent size. If manure was required in 3 months, an extra turning could be given to the mass 4 weeks after the first. If manuring season was far ahead, after the first turning the heaps could bemade dome-shaped and plastered well all over with cattle dung, alone or mixed with canal mud. Such a simple device, while allowing semi-aerobic fermentation to proceed slowly to complete ripening of the manure, offers protection to compost heaps from sun, rain and free aeration and helps in conservation of manurial ingredients, otherwise likely to undergo rapid loss. The fermentation was generally complete in 3 months (in dry season) to 5 months (in rainy season), when compost lumps could be broken down to finely divided brown powder resembling leaf mould. The average volume of per capita production of manure per day was 110 ft3 [3.1 m3] of fresh compost.”

Basak tabulates the analyses of water hyacinth compost compared with town compost and farmyard manure.

Chemical composition of compost manures (dried)

 Water hyacinth compostTown compostFarmyard manure
1. Nitrogen2.051.00.50
2. Phosphoric acid (p2O5)
3. Potash (K2O)2.500.800.30
4. Lime (CaO)3.913.0 to 5.00.2
5. C/N ratio131012 to 13

Bates, R.P. and J.F. Hentges, 1976 Aquatic weeds - eradicate or cultivate? Econ.Bot., 30(1): 39–50

In a general review of the utilization of aquatic weeds the authors state: “The simplest and least costly conversion which can be accomplished is merely to compost the aquatic plants. Suitable compost has been produced, although plant nitrogen conversion to nitrate is not ideal. There is some indication that soil microflora can be adversely influenced by improper aquatic weed addition to soils. Thus the complex interactions between plant material, soil and microflora will require detailed study, if practical soil conditioning uses are to evolve.”

Boyd, C.E., 1974 7. Utilization of aquatic plants. In Aquatic vegetation and its use and control, edited by D.S. Mitchell. Paris, Unesco, pp.107–14

The author reports that Salvinia molesta has been used as a mulch on gardens in the vicinity of Lake Kariba. It is particularly useful if mixed with the dung from game animals such as elephant or buffalo, or when placed in a chicken run for some days so that it partially dries out and becomes mixed with the chicken droppings.

Chokder, A.H., 1968 Further investigations on control of aquatic vegetation in fisheries. Agric.Pak. 19(1):101–18

The author states that water hyacinth ash has a commercial value as a base for fertilizers, especially potash fertilizers. It contains 25–27% K as K2O. Other plant nutrients in the ash are of negligible importance. The ash has more value for fertilizer than other preparations of water hyacinth.

*Day, F.W.F., 1918 Water hyacinth as a source of potash. Agric.Bull.Fed.Malay States, 6(7/8): 309–14

The author describes the manurial value of water hyacinth especially in regard to its potash content, which is particularly high in the stalks. He describes methods of burning the plant and collecting and storing the ash. He adds: “Experience will show whether a little lime should be mixed with the ash as probably this would keep the phosphate in the residue.”

*Finlow, R.S. and K. McLean, 1917 Water hyacinth and its value as a fertilizer. Calcutta, India, Govt. Printer, 16 p.

Experiments on the use of water hyacinth as a fertilizer for jute were carried out either after the hyacinth had been heaped and allowed to rot or after burning to ash.

“For tests on the jute crop about 30 tons of fresh hyacinth was collected in Dacca. Some of this was heaped and allowed to rot and the remainder dried and burnt. There was a considerable loss of liquid squeezed out from the rotted material which resulted in a loss of potash as shown by the following:

100 parts by weight of fresh hyacinth yielded: after rotting - 6.6 lb [3 Kg] K2O after burning - 30.5 lb [14 Kg] K2O

There was thus a loss from rotting material of 70% available potash, and 60% of the nitrogen was also lost. It is thus recommended that hyacinth before stacking should be partly dried, or alternatively fresh hyacinth should be mixed with earth or dry plant material in the stack.

On a total of about 72 plots, of which 22 were checks, a variety of treatments were applied including rotted hyacinth, rotted Pistia, hyacinth ash and various fertilizers including potassium sulphate and potassium chloride. The results gave a clear indication of marked response of jute to potash (about 25% increase in yield) a result which was also obtained when hyacinth ash containing an equivalent amount of potash (94 lb K2O/acre) [105 Kg/ha] was applied. Good results were also obtained from rotted Pistia.

In Bengal water hyacinth contains considerable stores of plant food of which potash is the chief constituent. If rotted, the residue contains about the same amounts, or more, of nitrogen and phosphoric acid as ordinary farmyard manure; and it is several times as rich in potash: it has about the same water content (60%). The dried hyacinth material weighs about one-twentieth of the fresh and thus is in a more convenient form to transport. It contains from 1.5 to 2% of nitrogen and about 8% of potash.

After burning, the ash residues of clean water hyacinth (unmixed with earth) have been found to contain as much as 35% of potash (K2O), and an average figure for the Dacca district would seem to be over 25%. The ash is therefore several times richer in potash than ordinary wood ashes.

The results of the field tests showed conclusively that water hyacinth is a valuable manure either in the rotted state or as ash on laterite soils of the old alluvium in Bengal. Some of the various silts of the new alluvial tracts exhibit potash deficiency and there is little doubt that hyacinth, either rotted or as ash, will prove equally valuable for them. On the high, light, well drained soils the rotted material may be preferable but on heavy low–lying lands the ash would probably be more successful.”

*Gratch, H.I., 1968 Water hyacinth - a menace that could be turned to a blessing. In Handbook of utilization of aquatic plants, edited by E.C.S. Little, Rome, FAO, Plant Protection and Production Division, PL:CP/20:16

The author estimates that about 200 000 ha of water bodies throughout India are infested with water hyacinth and carry about 250 t/ha. As about 10 t of compost can be made from 100 t of water hyacinth there is a potential of about 5 million t of compost. He cites the analysis given by Basak (1948). He contends that the cost of making the compost is mainly derived from the labour needed to harvest it and make the heaps. The compost should be used at the rate of 5–7.5 t/ha. Preferably it should be fortified by mixing in superphosphate at the rate of 1 part of super to 20 parts of compost. The clearing of the hyacinth and using it for compost would not only lead to increased crop production but also would increase fish yields in the tanks from which the weed was cleared.

Hortenstine, C.C. and J.V. Parra, 1973 Water hyacinths as a soil amendment and source of plant nutrients. Abstr.Meet.Weed Sci.Soc.Am., 1973

Control measures for water hyacinth which use chemicals allow the plants to become part of the detritus and thus create a permanent sink for plant nutrients. Complete removal of the hyacinth with subsequent disposal in soil would alleviate this nuisance in affected waters, lower the nutrient content of these waters and benefit the soil, especially sandy soils. Normal soil has an average C/N ratio between 9 and 12 which is maintained at almost a fixed value. Therefore when organic matter with a C/N ratio greater than 12 is added to soil, micro-organisms must draw upon the soil N in order to assimilate the added C; water hyacinths generally have a C/N ratio between 25 and 30. (From Weed Abstracts)

*India, 1952 Council of Scientific and Industrial Research, The wealth of India. Vol. 3. Raw materials. New Delhi, CSIR, pp.130–4

In a review of utilization of water hyacinth it is stated that the laterite soils of the old alluvium of Bengal and some types of silt comprising the new alluvial tracts are deficient in K, P and lime. So water hyacinth, either rotted or ashed, is a valuable manure for them. For light, well-drained soils the rotted material may be preferred; for heavy low-lying lands the ash may be used with advantage.

Water hyacinth, mixed with earth, cow dung and wood ashes in the Chinese compost fashion gives a compost in about two months. It is necessary to use wilted rather than fresh plants in the compost heap as due to the high water content the juice from the fresh plants is expelled and lost during stacking.

Hyacinth compost contains on an average (dry matter basis):

N - 2.05%; P (as P2O5) - 1.1%; K (as K2O) - 2.5%; Ca (as CaO) - 3.9%;

and the C/N ratio is 13. Bulk for bulk hyacinth compost is twice as rich as town compost and four times as rich as farmyard manure in K. It is eminently suitable for jute and rice fields, for vegetable gardening and fruit growing. It can be produced at low cost and large-scale trials have demonstrated that water hyacinth control through composting is both practical and profitable.

Kamal, I.A. and E.C.S. Little, 1970 The potential utilization of water hyacinth for horticulture in the Sudan. PANS, 16 (3):488–96

The World Food Programme initiated a project to encourage the removal of water hyacinth from the Nile river by hand (see also Chapter IV) and then to put it to use for horticulture as mulch and/or fertilizer. Experiments were carried out to determine the rate of drying of fresh hyacinth as a means of reducing the cost and difficulty of transportation, and to improve the condition of the material for composting. Trials were also carried out, at different sites, on the effectiveness of layers of hyacinth of different thicknesses as means of killing or suppressing infestations of two of the most difficult and persistent weeds, Cyperus rotundus and Cynodon dactylon.

The following tables summarize the results of the weed control trials:

Control of weeds (mostly Cynodon dactylon and Cyperus rotundus) by different thicknesses of water hyacinth mulch. Weed cover at time of treatment was 100%

Table 1 Trial 1
No.of layers of hyacinth applied 24 Jan.Effect on aerial parts of weeds
13 February (after 21 days)23 April (after 59 days)25 October (after 275 days)
No coverNochangeNo changeNo change
2 layersEtiolation60% dead100% dead
3 layersEtiolation80% dead100% dead
4 layersEtiolation80% dead100% dead
6 layersEtiolation80% dead100% dead
Table 2 Trials 2 and 3
No of layers of hyacinth applied 25 Jan.Effect on aerial parts of weeds
25 April (after 90 days)6 September (after 225 days)
 Trial 2Trial 3Trial 2Trial 3
No coverNo changeNo changeNo changeNo change
1 layer40–50% kill60% kill20% kill20–50% kill
2 layers60–90% kill50–100% kill50–60% kill90–100%kill
3 layers60–100% kill60–100% kill70–100% kill95–100% kill

The following table summarizes the results of composting trials. The pits were made 2 m x 1 m and 0.5–1.0 m deep. When using cow dung or soil these were added in layers 2–3 cm deep at every 20–30 cm height of the pile.

Results from composting water hyacinth by different methods

Method (pits made 24 Jan)Results observed
24 April6 September (after rainy season)
1. Fresh hyacinth aloneVery little decompositionPatchy decomposition
2. Fresh hyacinth with cow dung layersDecomposed to depth of 40 cmDecomposed completely
3. Dried hyacinth with cow dung layersLittle decompositionDecomposed to a depth of 95 cm

The authors make the following conclusions and recommendations:

“Hyacinth can be fully sun-dried before using as mulch. Using hyacinth for mulch could consume large quantities of the weed, especially if employed on the more important crops such as cotton or sorghum. After 8-12 months the mulch could be worked into the soil.

Compost from hyacinth. Good compost can be made from hyacinth but further research is needed to determine the most efficient method. Neither fresh material nor completely dry material appears suitable, though dry material might be satisfactory if the right amount of water were added to the clamp. It is estimated that hyacinth dried to about half its fresh weight may be the most suitable. Addition of layers of manure is clearly beneficial but layers of soil may be an adequate alternative. Digging of compost pits in the conventional way near the river banks may lead to damage from a rising water when the river is at a high level. Compost clamps built on the soil surface are thus preferable.

The amount of compost required by soils near the Nile and its tributaries may be 100-125 tonnes/ha for which some 500–625 tonnes of fresh material would be needed.

The effect on the viability of hyacinth seeds after composting should be determined to assess the safety of moving compost any substantial distance from the area of collection.

Burning hyacinth: Hyacinth completely or partially burnt after drying would produce a product of fertilizer value though lacking in some or all of its nitrogen content.”

Mara, M.J., 1976 Estimated values for selected water hyacinth by-products. Econ.Bot., 30(4): 383–7

The author reviews the value of various by-products which can be obtained from water hyacinth. The calculations are based on demand and supply in the U.S.A. and on local currency. Though the prices are, of course, no longer applicable a summarized version is given below because relative costsmay remain applicable.

  1. Plotting compost. In 1973 the production costs for a finished compost made with half water hyacinth and half peat was US$1.31/bushel (36.4 litres). It was sold at US$1.75/bushel. Thus the firm manufacturing the product could pay at most US$0.44 for the water hyacinth needed per bushel of dry compost. This amount converts to US$98.20/ dry ton or, at most, US$6.42/wet ton (this calculation was based on 21.7 bushels/cubic yard (0.76 m3) and 5.14 cubic yards/ton). The wet to dry ratio of water hyacinth was found to be 15.3 and was constant throughout the growing season (but with a standard deviation of 2.1). This worked out at a water content of the hyacinth of 93.4%. Mara considered that the market at this calculated price might not be large.

  2. Soil amendment. Mara states that water hyacinths may have some value as compost when used alone. If hyacinths are used as a soil amendment their value must cover the costs of transporting, spreading and working them into the soil. The fertilizer value (1974) of 1 t of water hyacinth was approximately US$0.30 based on the assumption that 300 t of hyacinth is equivalent to 1 t of 8–8–8 fertilizer. Additional to this value the hyacinths would be worth something for the improvement they would give to the soil. Transportation cost was estimated at US$0.27/ton/mile (1.6 km). This cost suggests that hyacinths would not be in demand as compost by farmers located more than one mile from the source of supply. If all costs were considered it is doubtful whether any hyacinths would be wanted for soil amendment at even this relatively short distance.

Mohamed, B.F. and F.F. Bebawi, 1973 Burning as a supporting treatment in controlling water hyacinth in the Sudan. 1. Routine burning. Hyacinth Control J., 11:31–4

Mohamed, 1973a Burning as a supporting management in the control of water hyacinth in the Sudan. 2. Back burning. Hyacinth Control J., 11:34–7

The authors describe methods of efficient burning of dried mounds and carpets of water hyacinth, either harvested into piles or deposited onto the banks by flooding. The papers are concerned primarily with the destruction of the plant accumulations and particularly of viable seeds that they contained. However the papers are cited because they could be useful to those interested in retrieving the ash from such fires for fertilizer purposes. A warning is given that seeds may not always be destroyed if the temperature of the fire does not reach an adequate level due to the presence of insufficiently dry material in the piles.

Moore, A.W., 1969 Azolla: biology and agronomic significance. Bot.Rev., 35(1):17–34

Reviewing the literature on Azolla spp. Moore describes the nitrogen-fixing capacity of this water fern which is attributed to its symbiotic relationship with a blue-green alga, Anabaena azollae. This yields and amount of N fixed are given in Chapter III.) Thus Azolla has clearly a potential value as a fertilizer. It has been used extensively in Vietnam as a green manure for rice which is harvested in May and June. For 20 years the Ministry of Agriculture in North Vietnam organized over 1 000 depots for multiplying Azolla for the farmers. In 1957 it was claimed that 90 000 ha had been fertilized with Azolla with consequent increase in rice production. The best periods for vegetative growth of Azolla are during August-September and January-February. At these times the plants double in number every 5–7 days, when the temperature is optimum at 16–17 C. Just before, or after, rice transplanting Azolla is scattered in the fields, at a rate of about 10 m2/ha, and it grows along with the rice during January and February. Towards the end of March the temperature rises to a mean of 22–24 C when the Azolla dries off and forms a sediment on the bottom. The rice is at the boot stage at this time and starts to become greener. Growth and tillering then accelerate. By the time of harvest (May-June) little or no Azolla remains. Trials have measured a 14% increase in rice yield from this treatment.

Another trial with rice in North Vietnam gave a yield of 1 760 kg/ha from an untreated control plot; 2 500 kg/ha from a plot to which 5 000 kg/ha of manure had been added, and 3 500 kg/ha from a plot with 2 500 kg of manure plus Azolla.

Moore comments: “Azolla appears to be capable of fixing N in the field in a similar way to a leguminous crop. So it can be considered to have a potential value in paddy rice cultivation provided the rice crop is not preceded by a legume, nor fertilized directly with N fertilizer. However since this practice is used traditionally in only a limited area of S.E. Asia it suggests that problems of management are involved. In Japan Azolla in the rice crop is considered to be a weed. Under these circumstances it may have a role as a green manure in unused paddy fields. Azolla must be killed before the N it contains becomes available. So it may be that it is the convenient rise in temperature in North Vietnam a month before the May-June harvest which kills the Azolla and makes it useful as a fertilizer. In most tropical rice-growing areas temperatures decline during the growing season.”

Parra, J.V., 1975 Use of water hyacinth as a soil amendment and source of plant nutrients. Diss.Abstr.Int.(B), 36(2):1016–17

Water hyacinth was used as a soil amendment and fertilizer in greenhouse and field experiments in FLorida, U.S.A. Optimum levels of water hyacinth for maximum yield were above 4 000 ppm in Arredondo fine sand. For Lakeland and Leon fine sands optimum levels varied between 6 000 and 8 000 ppm. Nutrient uptake was enhanced by hyacinth applications in all soils. Residual effects of hyacinth resulted in higher C, N, K, Ca, Mg and Mn content of all soils. The Zn content of Lakeland and Leon soils was increased and exchangeable Al reduced.

In the field, water hyacinth rates of 0, 15 000 and 30 000 kg/ha (dry matter) were incorporated in Wachula fine sand. Pearl millet, Pennisetum americanum, was grown as indicator crop. Basal fertilizer rates were N—P—K at 0–0–0, 30–13–25, and 60–26–50 kg/ha. After the first harvest 80 kg/ha was applied to all treatments. Two harvests were collected and analysed for nutrient uptake. Pearl millet yields were higher on all water hyacinth treatments than on fertilizer treatments. In the second harvest basal fertilizer depressed yields and nutrient uptake on plots amended with water hyacinths. The optimum level for maximum yield was 27 000 kg/ha of water hyacinths. The content of C, N, P, K, Ca, Mg, Zn, Mn and Cl, and effective cation exchange capacity of Wachula fine sand were increased by addition of water hyacinth. Soil pH was not affected as the soil was limed prior to water hyacinth incorporation.

Parra, J.V. and C.C. Hortenstine, 1974 Plant nutritional content of some Florida water hyacinths and response by pearl millet to incorporation of water hyacinths in three soil types. Hyacinth Control J., 12:85–90

Pot experiments were carried out in Florida, U.S.A., to measure the fertilizing effect of water hyacinths in three different soils. The plants were dried and ground and added at 0, 2 231, 4 462 and 8 924 ppm to the soils with and without added fertilizer. Pearl millet, Pennisetum typhoides, was used as the test crop.

One soil, Arrendondo, pH 6.5, had nearly ideal characteristics for plant growth. The addition of water hyacinth did not increase millet yield in the first crop, but when included in addition to fertilizer there was a positive response over and above the response to fertilizer alone. Fertilizer in terms of N-P-K was added at 0,0,0; 45, 25, 50; and 90, 50, 100 ppm. For the second millet crop in the same pots yields were much less than for the first crop and the residual effect of fertilizer alone was not significant. However there was a residual effect from water hyacinth with or without added fertilizer. Water hyacinth appeared to enhance nutrient uptake through a possible improvement of the root environment in addition to maintaining a source of plant nutrients.

On a less fertile sandy soil, Lakeland, pH 5.0, there was a greater response by the crop both to fertilizer and water hyacinth applications with greater residual effects. The best response was to the lowest rate of water hyacinth application.

The least fertile soil, Leon sand, pH 4.8, gave the biggest responses, with water hyacinth alone giving as good or better yields than fertilizers alone. Second crops were also better, reaching 74% of the first crop yields. In addition to increasing yield, water hyacinth applications increased N–P–K uptake by both crops of millet.

The authors comment that the relatively high 7.5 pH of the water hyacinth would certainly be a beneficial characteristic where large quantities of water hyacinths are disposed of on sandy acidic soils. The high base content would also probably be effective in reducing aluminium toxicity in unlimed soils.

Parra, J.V. and C.C. Hortenstine, 1976 Response by pearl millet to soil incorporation of water hyacinths. J.Aquat.Plant Manage., 14:75–9

The material in this paper describes in more detail the results reported in Parra (1975).

In the introduction, in which literature is briefly reviewed, the authors state that organic sources of nutrients, particularly organic N compounds and organic chelates of heavy metals, may have unique value in plant nutrition under some circumstances because of their solubility, or because of their steady release of available forms of nutrient elements. The benefits to be derived from the incorporation of organic matter into the soil are well known, and become of paramount importance in sandy soils which are low in organic matter and deficient in most plant nutrients. Water hyacinths contain fairly high concentrations of plant nutrients as compared to other species and would be very desirable green manures.

Reimer, D.N. and S.J. Toth, 1969 A survey of the chemical composition of Potamogeton and Myriophyllum in New Jersey. Weed Sci., 17(2):219–23

Reimer, 1970, Chemical composition of five species of Nymphaeaceae. Weed Sci., 18(1): 4–6

The authors carried out analyses of Potamogeton spp, Myriophyllum spp andother genera in the family Nymphaeaceae (see Chapter III).

In the 1969 paper they refer to the wide variation in composition of aquatic plants andexplain their interest in respect of the utilization of such plants for composts. They state: “Itis recognized that when the total N content of plant tissue is between 1.5–2.0%, or higher,no extra N need be added to ensure proper decomposition of residues. The analytical data indicate that species of Myriophyllum andPotamogeton contain sufficient total N for decomposition. Partial drying of the cut plants before composting however will be necessary to reduce anaerobic decomposition to a minimum. The final composts prepared from the aquatic plants probably will contain fairly high amounts of minor elements, especially Fe, Mn and Zn which may be beneficial. It is believed that the composts will need the addition of extra P and K.”

In the 1970 paper hey conclude: “In the previous paper it was pointed out that plants with 1.5–2.0% N or higher do not require addition of extra N for composting. Of the tissues reported in this paper only the petioles of Nuphar advena, Nymphaea odorata, and Nymphaea tuberosa fall below these values. The leaf blades of these species and the top growth of Brasenia schreberi and Cabombacaroliniana contain sufficient Nfor decomposition.”

“It wasalso pointed out in the previous paper that partial drying of the cut plants probably would be necessary to reduce anaerobic decomposition to a minimum. Except for Cabomba the Nymphaeceae reportedon here are coarse in structure and excess water should drain off quite readily and affort little problem.”

Riemer, B.N.and S.J. Toth, 1971 Nitrification of aquatic weed tissues in soil. Hyacinth Control J., 9(1):34–6

This paper describes laboratory test sof the potential usefulness of 16 aquatic weeds for disposal, after harvesting,by composting. The objective was to determine the rateand degreeof nitrification of dried, ground aquatic weed tissues when added to soil under aerobic conditions. The weeds were compared with untreated soil, alfalfa (lucerne) and ammonium sulphate, which is an easily nitrified source of nitrogen. Over a period of eight weeks the amountof nitrogen in the plant tissue which was nitrified in the soil was measured. Considerable variations were observed. Myriophyllum heterophyllum and Elodea canadensis nitrified at aboutthe same rate as alfalfa (20–25%. Cabomba caroliniana did not nitrify at all. In another test Nuphar advena nitrified to 58%, which was much higher than alfalfa, but the leaf petioles did not nitrify. Phragmites communis was much lower, as was Peltandra virginica (12–15%).

In a further test with P. communis itwas found that young plants (0.5 m tall) with a high N content gave moderate nitrification but that older plants (2–3 m tall) not only did not nitrify but they inhibited nitrification of the nitrogen already in the test soil.

In a final test Lemna minor gave a higher nitrification rate than alfalfa (40–50%). Utricularia sp. was equivalent to alfalfa. Potanogeton pulcher, P. cordata and Sparganium sp. all gave negative nitrification results.

The following conclusions were drawn:

  1. Aquatic plants show great variation in the conversionof plant nitrogen to nitrates by soil micro-organisms.

  2. Some tissues not only show poor nitrification but inhibit nitrification. This may be due to chemical inhibitors, or to high carbon-nitrogen ratios. Alternatively highmicrobial populations utilize nitrates so fast that low nitrate values are obtained.

  3. The older plants of one emergent species (Phragmites) appear to inhibit nitrification. No data are available for floating or submerged species.

  4. Some aquatic weeds may be composted for agricultural use without the addition of extra nitrogen, but not all.

*Schultz, H., 1962 Brazil's big-lipped Indians. Natl. Gogr.Mag., 121(1):118—33

A traditional method used by native Indians in Brazil is to burn water hyacinth as a source of potash in place of common salt.

*Singh, S.B., 1963 Preliminary experiments on the relative manurial values of some aquatic weeds as composts. Proc.IPFC, 10(2):141–5

Five aquatic plants were composted at the Central Inland Fisheries Research Substation, Cuttack, India, and their analyses compared with that of cow dung and garden soil as shown in the following table:

CompostpHOrganic C %Available N mg/100 gAvailable P mg/100g
Pistia sp.7.51.338.110.1
Hydrilla sp.8.21.959.96.6
Najas sp.
Ottelia sp.7.51.448.710.1
Eichhornia sp.
Dry cow dung-
Garden soil7.60.822.46.6

In preparing the composts in pits it was found best to air-dry the weeds for a day or two first. For composting the plants were mixed with equal quantities of soil and dry cow dung in early experiments. In later experiments the cow dung was omitted in order to improve comparisons between the different plants. Fibrous plants like Hydrilla and Najas and the roots of Eichhornia and Pistia took a comparatively long time to decompose. Hydrilla compost took 1 1/2 months to get ready; the others took one month.

Crops of tomatoes and lady's finger were grown on plots to which these composts had been added at the rate of 28 tonnes/ha, in four weekly applications of 7 tonnes/ha.

The conclusions from the trials were that the yield of tomatoes and lady's finger were increased by all the water plant composts exceptEichhornia, which consistently gave yields lower than crops grown in the garden soil only. The author, however, feels that his results show that water plant composts are useful for manuring fish ponds or as agricultural fertilizer. He suggests that composts appropriate to the nutrient needs of various crops could be prepared by a judicious mixture of water plants having the necessary analysis of plant nutrients.

Subagyo, T. and N.V. Vuong, 1975 Biological studies of Salvinia molesta. BIOTROP Newal., (12)

Dead masses of Salvinia molesta stimulated the growth of rice seedlings in Indonesia. No significant difference was found between the use of fresh or dry material as a mulch on the growth or rice seedlings. The mulch increased the dry weigh by 40% and the number of tillers by 30% of lowland rice seedlings six weeks after planting. (From Weed Abstracts)

Sudan, National Council for Research, Agricultural Research Council, 1975 Aquatic weed management: some prospects for the Sudan and the Nile Basin. Report of a Workshop held 24–29 November 1975. Khartoum, Sudan, National Council for Research, 157 p.

This book rports on the work of Abdalla and Hafeez, 1969 (see also p.114). Reference is also made to the usefulness of water hyacinth compost, claimed to be equivalent to farm yard manure in respect of N and P content, and having a much higher content of K.

Thompson, T.W. and H. Hartwig, 1973 Control of watermilfoil inlarge Wisconsin lakes. Hyacinth Control J. 11:20—3

The authors report the successful disposal of Myriophyllum spicatum and M. heterophyllum as a soil conditioner. The plants were prepared by chopping and dewatering.

*Watson, E.P., 1947 The utilization of water hyacinth. Indian Farming, 891):29–30

After pointing out the usefulness of compost the author describes how it can bemade from water hyacinth.

“Water hyacinth should not be composted in the fresh green state, otherwise it will settle down into the sortof soggy mass that we see when itis piled on the edges of tanks. Nor shoulditbecomebone-dry asthat would necessitate gettingit allmoist again. If when removed it is spread out in a thin layer to wilt in the sun for a week or two,it will be just about right. Even then to avoid its compacting into a solid mass through which air cannot penetrate, it is always best tomix some other material such as rough dry grass, wilted jungle or fallen leaves with it.

“The simplest way of making compost in the first instance, and until oneunderstands the process sufficiently well totackle iton alarge scale, is to use a circular framework made of bamboo. A convenient size is 5 ft diameter [1.5 m] at base, 4 ft [1.4 m] high and 4 ft 6 in. [1.37 m] diameter at top. This taper is to enable it to be lifted off without sticking. This should be put up on a plot ofwell-dug earth and roughly mud-plastered inside except for the bottom 6 inches [15 cm]; this is to prevent strong winds blowing through it.

“The well-wilted water hyacinth, together with any other vegetable refuse available, is spread evenly in a layer about 9 in. [22 cm] thick. Over this a layer of any fresh manure is put an inch [2.5 cm] or more thick; urine-soaked bedding is best of all. Then a layer of wood ashes, or finely powdered earth, is evenly scattered over the whole; that obtained from the scraping of cattle stances or the cleaning of drains is the best but it must be dry and finely powdered to spread evenly.

“Turn over the whole two or three times to get it thoroughly mixed. Every leaf should have a little manure and a little earth adhering to it. Then stick a 5 ft [1.5 m] bamboo lightly into the ground in themiddle of the bamboo framework and toss all the material in round it, piling up as much on the top as can be managed to stay. Leave for four days (by which time it should have settled to half the height) andremove the central bamboo stake, the bottom of which should be too hot to touch if the material has been mixed properly.

“The aeration hole thus left will start smoking at once. Failure to heat up generally means that the material has been mixed too wet which helps making silage instead of compost. If this is the case lift off the bamboo framework, spread all the material out for an hour or two to dry a little and then refill as before. The heap should continue stemin for a fortnight and then slowly cool downn. If it cools too quickly, it probably indicates stinted wood ashes and earth.

“After 20 days the framework can be lifted off and set up alongside while the still hot material (which should now be completely covered with grey fungus mycelium) is mixed and reloaded in it. Any over-dry parts should be put in the middle this time and overdamp parts round the edge. The bamboo pole should be put in as before and removed after four days. In another 10 days the framework can be removed altogether and used again for starting a fresh compost heap.

“The first made heap should be left two months to ripen, after which (three months from the start) it will have become a brown friable compost ready for immediate use. Nothing needs to be done to it during this time beyond an occasional light watering of the outside, should the weather be very dry. If not wanted at once it should be stored under cover or the tops of heaps made conical and covered with a little earth to ward off heavy rain.”

*Anon., 1966 Notes and news. Mulching with water hyacinth (Eichhornia crassipes). Two Bud, Newsl.Tea Res.Assoc.Tocklai Exp.Stn., 13:31

The author describes the mulching of tea bushes with water hyacinth in India.

“There is usually an abundant supply of water hyacinth in most estates. Itis extremely good for use as a mulch in young tea areas during the dry period for conservation of soil moisture. Inthe droughty regions, particularly in the hot southern slopes of the teelas in Cachar, this is of particular benefit. The plants are best used wet, as this adds some moisture as well to the soil. This mulch slows downthe rate of evaporation from the soil. It also keeps the soil surface permeable and reduces the run-off of the rain and consequently reduces the amount of soil the water can carry away, and increases the proportion of the rain or irrigation water that percolates into the soil. Mulching can, therefore, be used with advantage in irrigated areas as well.

“The water hyacinth plants are of great manurial value as well and the dried ones of the local varieties contain about 70% organic matter, 1.5% nitrogen, 0.6% phosphorus and about 5.5% potash. When the dry period is over, all the undecomposed matter should be removed from near the collars of the bushes and heaped in between the rows of tea till completely decomposed. The soils of all poor tea areas are normally very deficient in organic matter and mulching with water hyacinth will not only add the minerals deficient in the soil but will also improve the physical texture.”

Knapsack sprayer in dug-out canoe used for weed control on Rawa Peninglake, Central Java, Indonesia

Working carrying fresh hyacinth to mulch plots (left) at Malakal on the Nile river, Sudan. Ploths for drying experiment on right

A completed compost clamp covered with a layer of earth. In the background are plots with diferent thicknesses of fresh water hyacinth applied as a much

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