III. WATER, MINERAL AND PROTEIN CONTENT AND PRODUCTIVITY OF AQUATIC PLANTS

The ingredients, other than water, of aquatic plants are similar to those in plants adapted to growth on dry land. The literature contains the results of numerous analyses taken of different species growing in a range of habitats in many countries. A general criticism against the usefulness of aquatic plants is that their high water content makes them inconvenient to harvest and also unsuitable as fodder for livestock. Moreover, it is often alleged that the plants are low in useful nutrients.

Thereforea study of these various results should be interesting and helpful tothose considering the utilization of aquatic plants for their own particular needs.

Probably the most comprehensive analyses of aquatic plants has been done by C.E. Boyd, U.S.A., whose work will be repeatedly noted in the following pages. This work has culminated in an extensive review (Boyd and Scarsbrook, 1975) in which the data from 35 papers, all on work in the U.S.A., have been tabulated. Anyone studying the overall range of aquatic weed analyses should have a copy of this paper.

A brief but useful review on nutrient uptake by aquatic plants by J.J. Gaudet appears in a chapter in Mitchell (1974).

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

Water hyacinth analysis (% fresh weight) :

water = 90.2; N = 1.03; P = 0.42; K = 1.81; Ca = 0.02

The authors point out the high P content in water hyacinth compared with 0.24% in alfafa (lucerne).

^*Agrupis, F.M., 1953 The value of water hyacinth as silage. Philipp.Agric., 37(1–2):50–6

^*Alford, L.W., 1952 Alligator weed - a good cattle food. Chemurg.Dig., 2(9):10–2

Alligator weed (Alternanthera philoxeroides) - analysis of dry matter (100°C) (%):

Allenby, K.G., 1967 The manganese and calcium content of some aquatic plants and the water in which they grow. Hydrobiologia, 29:239–44

Analyses of Mn, Ca and ash of a range of aquatic plants (mean of several analyses):

The author comments that the Mn content of aquatic plants is several times greater than land species. There appeared to be no correlation between the amount of Mn in the plants and the water in which they grow. He also noted that the Ca to ash ratio of E. canadensis, S. ramosum and A. plantago is less than that of the water.

Allenby, K.G., 1968 Some analyses of aquatic plants and waters. Hydrobiologia, 32:486–90

Analyses (% or ppm dry weight) of a range of aquatic plants compared with the water in which they were growing (mean of several analyses):

The author draws attention to the high N. content of L. polyrhiza which was growing in high nitrogen water.

He also notes that chloride content of L. minor appeared to decrease with increasing chloride content of the water, while with L. polyrhiza the reverse appeared to be the case. With E. canadensis there appeared to be no relationship.

Anderson, R.R., R.G. Brown and R.D. Rappleye, 1966 The mineral content of Myriophyllum spicatum L. in relation to its aquatic environment. Ecology, 47:844–6

Analyses of Myriophyllum spicatum when grown in fresh water and in brackish water (ppm fresh weight):

The authors comment that M. spicatum appears to be capable of regulating salt uptake independently of concentrations in the aquatic environment. It can tolerate salt concentrations up to a maximum of 15 000 ppm.

^*Bailey, T.A., 1965 Commercial possibilities of dehydrated aquatic plants. Proc.Annu.Meet. South.Weed. Sci.Soc., 18:543–51

Citation of unpublished analyses of the dry matter of aquatic plants compared to common animal foods containing xanthophyll:

Analyses (mean of different harvests):

Estimated annual yields of E. densa = 6.5 tonnes/ha and of M. exalbescens = 8.4 tonnes/ha

The author concludes that it would appear that these dehydrated plants will average 840 mg of xanthophyll per kg, about 19% protein, and about 12% fibre.

Book, J.H., 1969 Productivity of the water hyacinth, Eichhornia crassipes (Mart.) Solms. Ecology, 50(3):460–4

Water content of water hyacinth (derived from the mean of 82 determinations) was 93.4%. The author notes that this content remained nearly constant throughout the growing season. After reviewing literature from several countries on daily production she points out that, in California, water hyacinth can, in spite of winter frosts, produce at a rate comparable with growth in the tropics.

Boyd, C.E., 1968 Fresh water plants: a potential source of protein. Econ.Bot., 22:359–68

The author has carried out analyses of many aquatic plants. Tannin content was included. He cites work at Auburn University, Alabama, U.S.A., which showed that high tannin interferes withprotein digestibility. Most high quality forage crops contain less than 2.3% (dry weight) of tannin. Thus plants containing more than 6–7% would be so low in digestibility as to be of little food value. The following table is quoted:

Dry Matter (D.M.) and Proximate Nutritional Analyses of Aquatic Plants

¹ Number of samples.

Five selected species were analysed, and their crude protein content analysed into amino acid content:

Amino Acid Analysis (% DM)

Boyd, C.E., 1968a Evaluation of some common aquatic weeds as possible feedstuffs. Hyacinth Control J., 7:26–7

The crude protein content of samples of 43 species of aquatic plants was determined and tannin analyses made. The author has summarized the results as follows:

Crude Protein Content (%DM)

Crude Protein Content (% fresh weight)

Boyd states that protein content declines rapidly with maturity. Therefore harvesting for fodder should be at maximum protein content related to total plant material. He adds that typical fresh forage crops have a protein content of 3–5%. Therefore to obtain comparable analyses aquatic plants would have to be partially dried.

Boyd, C.E., 1969 The nutritive value of three species of water weeds. Econ.Bot., 23:123–7

This article gives analytical data on Eichhornia crassipes, Pistia stratiotes and Hydrilla sp. not included in the author's previous publications. Protein, amino acid and plant nutrient analyses are given.

Amino Acid Composition of Water Weeds
% Dry weight

^a Sum of amino acids. Tryptophan analysis not obtained.

^b Essential amino acids.

Fertilizer Units for Water Weeds

Analyses of freshly harvested plants:

Inorganic nutrient analyses (% DM)

Boyd, C.E., 1969a Production, mineral nutrient absorption and biochemical assimilation by Justicia americana and Alternanthera philoxeroides. Arch.Hydrobiol., 66(2):139–60

Detailed studies were made of the nutrient uptake and production of Justicia americana and Alternanthera philoxeroides. The author observes that J. americana, an emergent species, absorbs large amounts of nutrients, especially N and P, early in the season. He suggests that this could have important ecological significance because it would deplete the water of these nutrients before the optimum condition for phytoplankton growth can occur. Thus the phytoplankton population would be effectively reduced and so lessen competition for nutrients later in the season. He speculates that if this feature is also the case for other vascular plants it would explain why many shallow-water lakes consistently produce large crops of vascular plants and small crops of phytoplankton. Moreover, if only some species of angiosperms have this ability to absorb and store particular nutrients early in the season it might explain why such species typically occur in dense, relatively monospecific, stands. The plant having stored a surplus of nutrients can use them and translocate them to growing points when environmental conditions are optimum.

It was found that more than 50% of the total absorption of ash and macronutrients (other than Mg) occurred prior to the first sampling date (mid-May). Though the standing crop of dry matter increased until mid-July no net uptake of N, S or Ca occurred past mid-June. Mg content doubled between mid-May and mid-June. Samples were taken from Lake Ogletree, Alabama, U.S.A., and a drainage ditch.

J. americana Analysis (dry weight) and crop amounts (g/m²) (Lake Ogletree):

A. philoxeroides Analyses (dry weight) and crop amounts (g/m²) (drainage ditch)

Boyd points out that A. philoxeroides also has the apparent ability to absorb large quantities of mineral nutrients prior to the period of maximum dry matter production. Though this plant and J.americana are strong competitors, yet they tend, when present together, to form individual monospecific stands without substantial mutual invasion.

Boyd, C.E., 1970 Production, mineral accumulation and pigment concentrations in Typha latifolia and Scirpus americanus. Ecology, 51(2):285–90

Maximum shoot standing crop of Typhalatifolia and Scirpusamericanus was recorded as 684 g/m². Levels of nutrients and pigments declined in both species as the plants aged, as shown in the following table:

Analysis (%) of nutrients in Typha seed heads:

N = 0.81; P = 0.23; S = 0.10; Ca = 0.25; Mg = 0.22; K = 2.41; Na = 0.07.

The most rapid uptake of several nutrients in both plants was found to occur earlier than maximum growth rates.

Boyd, C.E., 1970a Chemical analyses of some vascular aquatic plants. Arch.Hydrobiol., 67(1): 78–85

This paper contains analyses of various plants all collected from the same site (a 1 200-ha lake) in autumn.

The author draws attention to the wide interspecific differences in analysis from plants growing in water of the following chemical composition (ppm):

Macronutrient Contents (% DM)

Micronutrient Contents (ppm DM)

Pigment Contents

Boyd, C.E., 1970b Losses of mineral nutrients during decomposition of Typha latifolia. Arch.Hydrobiol., 66(4):511–7

The author determined the nutrient content of shoots removed from the plant and retained in bags held submerged beneath the surface of a lake, or suspended just above it. The experiment began in mid-winter.

T. latifolia - in submerged bags

The same general trends were evident, but at a slower rate, for the suspended material.

The author concludes that the initial increase of N was related to a build-up of microbial biomass. The rate of loss of N increased rapidly after 95 days and corresponded with the spring temperature increase. At the end of the experiment N losses corresponded to dry matter disappearance. Within the first 20 days leaching of nutrients resulted in the loss of most of the Na and K, 50% of the Ca and P, and 75% of the Mg. Thereafter nutrient losses were at about the same rate as dry matter degradation.

Data on nutrient loss of other plants (including terrestrials) as described in the literature, are reviewed.

Boyd, C.E., 1970c Vascular aquatic plants for mineral nutrient removal from polluted waters. Econ.Bot., 24:95–103

Yield of Eichhornia crassipes, Justicia americana, Alternanthera philoxeroides and Typha latifolia under continual culture:

Analyses of these plants are reviewed from the literature.

Boyd, C.E., 1970d Amino acid, protein and caloric content of vascular aquatic macrophytes. Ecology, 51(5):902–6

Typha latifolia and other aquatic plants were analysed.

Protein levels in T. latifolia decreased from 10.5% (dry weight) in April to 3.2% in July. The proportion of each amino acid in the protein did not change appreciably. Caloric values increased from 4 160 to 4 552 cal/g during the vegetative period.

Protein content of T. latifolia from different sites ranged from 4.0 to 11.9%. When plants grow in the same site protein variations indicate interspecific variation in protein synthesis. Crude protein is a fairly accurate estimate of actual protein in aquatic macrophytes though it may usually overestimate actual protein content by 10–20 %.

Protein and caloric content of plants from Par Pond, near Aiken, South Carolina, U.S.A.:

Amino acid composition (%) of T. latifolia protein at different stages of maturity:

Boyd, C.E., 1971 Leaf protein from aquatic plants. In IBP Handb., (20):44–9

Reviewing literature on yields of aquatic plants the author cites the following:

1. Floating species such as Eichhornia crassipes and Pistia stratiotes may have standing crops of 10 000 kg/ha and, because of vigorous growth might, under a continuous cropping system, yield up to 100 000 kg/ha. They have a high moisture content of 92–97% and contain 3–4% nitrogen. From water hyacinth (E. crassipes) only about 15% of the total N was recovered in leaf protein.

2. Submerged species can produce standing crops up to 5 000 kg/ha, seldom more. They contain 90% or more water and N levels range from 2–4%. Less than 30% of the total N of several species was extractable as leaf protein.

3. Species with floating leaves have comparatively small standing crops, e.g.

   Nymphaea odorata 1 800 kg/ha

   Brasenia schreberi 790 kg/ha

   Nelumbo lutea 990 kg/ha

   water and N contents are similar to floating species.

4. Emergent species, e.g. Typha latifolia, Arundo donax, Scirpus lacustris and Cyperus papyrus, may have standing crop yields of over 20 000 kg/ha.

Other yields recorded were:

Alternanthera philoxeroides standing crop: 8 000 kg/ha; protein: 480 kg/ha Justicia americana standing crop: 25 000 kg/ha; protein: 590 kg/ha Sagittaria latifolia protein: 362 kg/ha

The author points out that these values are as high as those reported for leaf protein yields of crop plants and emphasize the value of aquatic plants as a crop.

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

Data on analyses of various aquatic plants are reviewed, typical standing crop yields given, and these figures are compared with a typical fodder crop (alfalfa).

Analyses (% Dry weight)

The author points out that there are considerable variations in the concentrations of most chemical constituents in samples of an aquatic plant species and this makes it difficult to predict the usefulness of a particular stand of plants. Concentrations may very twofold or more when plants are harvested at similar stages of maturity but from different sites. For example, crude protein values from Typha latifolia shoots from 29 sites ranged from 5.4 to 13.2% of the dry weight. Concentrations of various constituents also increase, or decrease, as plants mature. The crude protein content of dried shoots of Justicia americana (from the same population) decreased from 23% in May to 13% in September.

Submerged and floating plants usually had higher values for crude protein than emergent or floating-leaved plants.

Large standing crops are found in tall emergent plants and values of 10–20 tons of shoots/ha are sometimes found in species such as Typha latifolia, Schoenoplectus (Scirpus) validus, Saururus cernuus, Panicum hemitonium and Juncus effusus. However, depending on the stage of growth of the plants, emergent species which produce large standing crops of dry matter usually have a higher fibre content and a lower protein content than emergent species which produce lower standing crops of dry matter. Thus species such as Justicia americana, Alternanthera philoxeroides and Pontederia cordata are of higher quality as feeds, though they normally have shoot standing crops of 4–8 t/ha. Large floating plants may also have large standing crops, and values of dry matter above 10 t/ha are commonly encountered in Eichhornia crassipes. Other floating plants usually have standing crops below 5 t/ha. Submerged and floating-leaved plants normally have standing crops of shoots which range from 1–5 t/ha.

Tannins decrease the digestibility of protein. Concentrations of tannin of 10% and more have been found in Myriophyllum brasiliense, Cabomba caroliniana, Ludwigia peruviana, L. stolonifera, Brasenia schreberi and Nymphaea odorata.

Inorganic elements are found in aquatic plants at concentrations within the range of values reported for crop plants and deserve no special mention. However, submerged aquatic plants from hard water often have marl encrustations on external surfaces which greatly increase the proportion of inorganic to organic matter. Ash values of 25–50% of the dry weight are common. Such plants would be of low nutritive value but would be useful as a calcium supplement in diets of low calcium content.

Boyd, C.E. and R.D. Blackburn, 1970. Seasonal changes in the proximate composition of some common aquatic weeds. Hyacinth Control J., 8(2):42–4

The authors have recorded the protein content of seven common aquatic plants (Alternanthera philoxeroides, Vallisneria americana, Hydrilla verticillata, Nuphar advena, Najas guadalupensis, Pistia stratiotes and Eichhornia crassipes (water hyacinth). They found no increase in protein content of any of these species as summer progressed. In A. Philoxeroides and N. advena there was a decline. They conclude that the protein content of emergent species declines with age. For submersed species protein content may remain static or fluctuate. When increases occur they are related to new growth.

Ash content in A. philoxeroides and V. americana declined with age, but in the others only fluctuated.

The paper gives analyses for each plant for each month from April to August inclusive. The means of these figures are given below:

The authors point out that analysis of the whole plant does not reveal the variation which often exists between the contents of different parts of the same plant. As an example they give the analysis of Justicia americana shoots:

Boyd, C.E. and L.W. Hess, 1970. Factors influencing shoot production and mineral nutrient levels in Typha latifolia. Ecology, 51(2):296–300

Analyses of Typha latifolia (means, % of dry weight):

Standing crop values ranged from 428–2 252 g/m² (average 951 g/m²).

The authors comment on the variability of mineral nutrient content. Maximum values for N, P, Ca and K were 3–5 times as large as minimum levels. The greatest amounts of S and Na exceeded the smallest by 10 and 20 times, respectively.

Boyd, C.E. and E. 1975 Scarsbrook, Chemical composition of aquatic weeds. In Proceedings of the Symposium on water quality and management through biological control. Gainesville, University of Florida, pp. 144–50

The analyses of about 80 species of aquatic plants from 35 papers published in the U.S.A. since 1921 are reviewed. The data are given infive tables, and include dry matter content, ash, crude protein, ether extract and fibre, also the minerals p, s, Ca, Mg, K, Na, Fe, Mn, Zn and Cu. The amino acid content of 22 species appears in Table 4 and the caloric content of 41 species in Table 5. The numbers of samples are shown from which the mean figures are derived, together with reference to the papers from which the data originated. Much of the information is listed under the different papers cited herein.

The authors comment that the wide variation in composition between species and within species was not unexpected. These variations can be due to variations in sampling methods and methods of analyses by different authors as well as the variations in content within the same species when growing in different sites and at different stages of growth.

^*Byers, M.,1961 Extraction of protein from the leaves of some plants growing in Ghana. J.Sci.Food Agric., 12: 20–30

Analyses of three common aquatic plants:

Caines, L.A., 1965 The phosphorous content of some aquatic macrophytes with special reference to seasonal fluctuations and applications of phosphate fertilizer. Hydrobiologia, 25:289–301

In studies of phosphorous content of various aquatic plants the analyses (whole plant) were:

The lake in which these plants were growing was later fertilized with calcium superphosphate (at 126 kg/ha). Only the last two species showed evidence of greater uptake. The analyses taken 14 days later were:

Analyses of the P content of two species of Myriophyllum, from two different lakes in Scotland, were made at intervals from spring to autumn (% dry weight):

The author points out the seasonal variation in P content of the plants which he says is related to their growing, flowering and fruiting phases. He showed that the highest concentration was found in the growing tips.

Chalmers, M.I., 1968 Report to World Food Programme on a visit to Sudan. In Animal production WFP. Mission report on animal nutrition in Sudan. Study on the use of water hyacinths in ruminant animal feeding and also as a means of weed control. Rome, FAO, Acc. No. 02787–68–WS

Analysis of water hyacinth:

¹ Lamina is about 1/5th by weight of the fresh green material.

Comparison of the analysis of water hyacinth on a dry basis with an ‘average’ straw and an ‘average’ hay. Ash compared with English pasture species:

The author concludes that water hyacinth has a high ash content and inadequate protein, which is found mainly in the lamina. The carbohydrate is mainly in the petiole.

Cifuentes, J. and L.O. Bagnall, 1976 Pressing characteristics of water hyacinth. J.Aquat. 1976 Plant Manage., 14:71–5

The paper gives details of water hyacinth analyses. Water content of the whole plant was 94.96% ± 0.38%.

Analysis of liquid pressed out of water hyacinth (at about 600 kPa about 70% of the water was expressed):

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

The paper describes in detail the manufacture of ash and compares the potassium content of the ash with that of various other plants, including trees and grasses. Detailed tables are given, from which the mean figures have been extracted:

Analysis of sun-dried plant

Water = 11.4%; organic matter = 61%; ash = 27.6%
Ash analysis (mean): K₂O = 15.3%; P₂O₅ = 2.8%; S0₃ = 13%

^* Dirven, J.G.P., 1965 The protein content of Surinam roughages. Qual.Plant.Mater.Veg., 12:172–84

Protein analyses of the dry matter of aquatic plants and grasses compared with indigenous and cultivated grasses:

Easley, J.F. and R.L. Shirley,1974. Nutrient elements for livestock in aquatic plants. Hyacinth Control J., 12:82–5

Analyses of Hydrilla verticillata, Eichhornia crassipes, Ceratophyllum demersum, Potamogeton pectinatus, Vallisneria americana and Najas guadalupensis for their value as stock food showed that the elements K, Mg, Cu, Zn and Mn were present at a range of concentrations similar to those of land plants. Na, Fe and Ca were higher, while P tended to be lower. E. crassipes (water hyacinth), exceptionally, had a lower Ca concentration (only 2%) (see Chapter VII).

Fekete, A., D. Riemer and H.L. Motto, 1972. Removal of Rhizoclonium from a pond and its relationship to dissolved nutrients. Proc.Northeast.Weed Sci.Soc., 26:193–6

The paper gives details of studies of a filamentous alga, Rhizoclonium sp. Analysis: N = 3.64 - 3.87%; P = 0.14 - 0.17%
Yield: 4 600 kg/ha dry weight.

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

Analyses of water hyacinth:

Hyacinth ash thus contains about 50% KCI.

(c) Comparison with Pistia stratiotes and cow dung at a common moisture content of 65%:

(d) Comparison between large plants growing in water courses in the city of Dacca and stunted plants in shallow water in red soil districts:

^* Fish, G.R. and G.M. Will, 1966 Fluctuations in the chemical composition of two lakeweeds from New Zealand. Weed Res., 6(4):346–9

Analyses (mean values) of Elodea canadensis and Lagarosiphon major:

The authors state that the data indicate that Lagarosiphon has a greater content of dry material than Elodea, a fact no doubt related to the more rigid and robust habit of the former. It also contained rather less potassium but much more magnesium than Elodea. Some seasonal variation appeared to occur in the mineral content of Elodea from Lake Okataina, which has a catchment largely of undisturbed native bush. The winter samples of plants from this lake had the highest content of N, P and K, but no seasonal variation was apparent in the analyses of samples from Lake Rotorua, probably because of the non-seasonal artificial eutrophy to which the lake is subjected.

Important differences were found between the Elodea samples from the two lakes. Those growing in Lake Okataina had lower contents of N, P and, in some cases, K. The clear water and low organic production that characterize this lake compared with Lake Rotorua support the view that the composition of Elodea reflects the quality of the water in which it grows. The present data suggest that Lagarosiphon probably reacts in a similar way.

Many aquatic plants, including Lagarosiphon and Elodea, are anchored to the bottom deposits of a lake or river by adventitious roots, but nutrients are probably absorbed mainly by leaves and stems in contact with the free water. Although the concentration of dissolved salts in the surrounding water will largely control the density and composition of these plants, the evidence indicated a difference in composition between species, even in the same lake, as well as seasonal changes. It follows that if these water weeds are to be exploited commercially, preliminary plant analyses are needed to determine the best species and season for harvesting.

Gortner, R.A., 1934 Lake vegetation as a possible source of forage. Science Wash., 80:531–3

Analyses of a range of aquatic plants for ash, protein and fibre compared with typical forage crops are given. The author points out that, with the exception only of Chara (which is uncommon), lake vegetation is characterized by high ash and protein content and low fibre. He suggests that legume hays are the only common forages which approximate to the lake weeds in these constituents.

Analyses (% Dry weight, mean results)

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

Water hyacinth analysis: Compost N = 2.05%; P₂O₅ = 1.1%; K₂O = 2.5% Yield = about 100 t/acre (250 tonnes/ha). Estimated area covered in India = 500 000 acres (200 000 ha).

Harper, H.J. and H.A. Daniel, 1935 Chemical composition of certain aquatic plants. Bot.Gaz., 96:186–9

The variation in N content of aquatic plants grown in different situations is discussed. Potamogeton foliosus and Typha latifolia were both low in N when growing in sandy soil and high in N on dark organic soil. The N and P content of the plants analysed were found to be higher than in common cultivated forage plants and weeds. The authors draw attention to the potentials of both species for “luxury consumption” of P by these plants from nutrient-rich situations. This is possibly the first reference to this attribute. The summarized, averaged, analyses of the aquatic plants are given below in comparison with the terrestrial plants.

The high Ca content of Elodea was attributed to encrustations on the surface.

^* Hossain, W., 1959 Investigation of water hyacinth as fodder. Agric.Pak., 10(4):513–8

Water hyacinth compared with napier grass (% dey matter basis):

Ingvason, P.A., 1969 The golden sedges of Iceland. World Crops, 21(3):218–20

Analysis of a semi-aquatic sedge, Carex lyngbei (local name ‘gulstör’) in comparison with a leading pasture grass, Poa pratensis (bluegrass):

Analytical work on Icelandic sedges which was done in Sweden about 60 years ago showed a crude protein content average of 10.2%, carbohydrates 45.5% and fibre 20.7%.

Knipling, E.B., S.H. West and W.T. Haller, 1971 Growth characteristics, yield potential and nutritive content of water hyacinths. Proc.Soil Crop Sci.Soc.Fla., 30:51–63

Water hyacinth analysis (% of dry matter):

N =1.75; Ca =3.06; P = 0.63; K = 3.07; Mg = 0.63

Optimum temperature for growth is stated as 28–30°C.

Koegel, R.G., 1973 et al., 1973 Increasing the efficiency of aquatic plant management through processing. Hyacinth Control J., 11:24–30

Analysis of Eurasian water milfoil, Myriophyllum spicatum:

Lancaster, R.J., M.R. Coup and J.W. Hughes, 1971 Toxicity of arsenic present in lakeweed. N.Z.Vet.J., 19(7):141–5

Analysis of three species of aquatic weeds compared with good pasture:

The authors do not comment on the substantial differences in analysis between the two samples of Lagarosiphon - especially the high ash content of the second sample.

Lawrence, J.M. and W.W. Mixon, 1970 Comparative nutrient content of aquatic plants from different habitats. Proc.Annu.Meet.South.Weed Sci.Soc., 23:306–10

Analyses of Eichhornia crassipes (water hyacinth), Alternanthera philoxeroides (alligator weed) and Justicia americana (water willow) from different habitats containing a wide range of nutrients, and covering a period of four years, are recorded. The results, averaged and summarized below, reveal the wide range of N, P and K the plants can contain if growing in water fertilized to various degrees with these elements.

The authors conclude that these results clearly demonstrate the variation in elemental composition of plants of the same species. They have shown how aquatic plants, when growing in water containing ample quantities of N, P and K, will exploit the situation by “luxury consumption” of these elements, far in excess of what they need for healthy growth. The plants growing in low N pools, for example, appeared just as healthy as those growing in water with high N from sewage. An extreme example was in K uptake by A. philoxeroides. In one case consumption was 20 times the content of plants grown in unfertilized pools (7.3% K compared with 0.36%).

Linn, J.G., 1975 et al., Nutritive value of dried or ensiled aquatic plants. 1. Chemical composition. J.Anim.Sci., 41(1):601–9