Journal of Scientific & Industrial ResearchVol. 60, May 2001, pp 378-382

Seaweeds As A Biofertilizer

S T Zodape

Central Salt and Marine Chemicals Research Institute, Bhavnagar 364 002

Seaweeds are large plants growing in the sea, especially various marine algae like the rock weeds, kelps, sea lettuce anddulses. Dried or fresh seaweeds and liquid extracts have been increasingly employed by horticulturists, gardeners, farmers, andorchadists as a fertilizer. Seaweed extracts are now commercially available as maxicrop, seasol, SM3, kelpak, and cytokin .Thceffect of seaweed extract is due to the microelements and plant growth regulators such as cytokinin present in it. Seaweed extractis used as a foliar spray, application to soil and for soaking of seeds before sowing. It enhances the germination of seeds,increases uptake of plant nutrients, and gives resistance to frost and fungal diseases. Seaweed extract is effective for ripening orfruits, increasing shelf-life of the produce, improves the quality of produce, and serves as an excellent soil conditioner.

IntroductionAs the population is growing at a fast rate, the

agrobased products should also increase. With theagrobased products, fertilizer industry is bound to grow,as it is one of the major components for increasing foodproduction. At present there is a shortage of about threeto four million tonnes of fertilizer'. As the disadvantagesof chemical fertilizers are becoming more apparent, farm-ers are slowly but surely turning towards organic fertil-izers. With increasing demand, availability of organicfertilizers from one or two sources is not adequate. Tomeet the increasing demand many viable options as pos-sible have to be explored? and one of such options is theuse of seaweeds as a fertilizer.

Seaweeds belong to a rather ill defined assemblageof plants known as the algae. The term" seaweed" itselfdoes not have any taxonomic value, but is rather a popu-lar term used to describe the common large attached(benthic) marine algae found in the groups ofChlorophyceae, Rhodophyceae, Phaeophyceae or green,red, and brown algae, respectively'.

Seaweed extracts have been marketed for severalyears as a fertilizer additives and beneficial results fromtheir use have been reported 4. Many claims have beenmade for seaweed extracts including better seed germi-nation and deeper root development, increased frost re-sistance, increased nutrient uptake and changes in plant

tissue composition, increased resistance to fungal dis-eases, reduced incidence of insect attack, higher yields,longer shelf-life of produce and improved animal healthwhen livestock is grazed on treated crops or pasture). Ithas been shown that the performance of seaweed ma-nure is superior to the conventional organic manure viz.,farm yard manure". Therefore the interest in seaweed asa fertilizer has been increasing as a supplemental fertil-izer, in which the importance is being given to be thesource of micro elements and as a soil conditioner",

Liquid extracts derived from marine algae have beenused over the past 40y on various crops to promotegrowth and development. Interest in these seaweed con-centrates (SWC) in agricultural system is focused on theiruse as an inexpensive source of naturally occurring plantgrowth regulator. Much of the benefit from the applica-tion of seaweed extract has been attributed to the pres-ence of the plant hormones, especially cytokinins. Vari-ous seaweed concentrates contain significant amount ofcytokinin in addition to other phytohorrnones x. The mainseaweed extracts known to playa useful role in agricul-ture are Maxicrop (seaborn), Algifert (marinure),GoemarGA 14, Kelpak G6, Seaspray, Seasol, SM3, Cylex andSeacrop l6(ref 9), Algistim'", and cytokin".

Work Done At CSMCRI, BhavnagarThivy' has studied the seaweeds as manure for veg-

etable and field crops. Bokil et al" continued the work

ZODAPE : SEAWEEDS AS A BIOFERTILIZER 379

and reported superior performance of seaweed manure over the conventional manure as farm yard manure. Rama Rao 12 has ca rr ied out work on liquid seaw eed fe rtilize r(LSF) and recorded promotiona l e ffec t o n Zizyphus mauritiana Lamk. S ince then, the work is con­

tinuing in thi s Institute ..

After doing exhaustive study, CSMCRI has been able to develop a process for manufacturing a liquid sea­weed fertilizer. Th e process is a lready bee n

commerciali sed by this Institute.

Some of the Methods for the Preparation of Liquid Seaweed Fertilizer

Seaweed ex tract is an organic manure and is benefi­cia l due to the presence of trace e lements and other o r­ganic substances such as amino acids, antibi ot ics, aux­ins , g ibbere llins and vitamins in it . Some of these sub­stances are decomposed by heat and hence it is essential that they should be conserved if they are to benefit the crops n. The method of ex traction and the spec ies used could be of great importance to the plant growth activity o f the ex tract. Many seaweed constituents are known to undergo marked seasonal variati ons, which are be ing considered, in both commercial seaweed ex tract produc­ti on and in the eva luation of incons istent fi e ld tri a l re­s ults~.

Many species have been reported to be used for the

preparation of LSF suc h as Funts vesiculata. Furcelaria fas ti g iata , Hyp nea 111ll sc ifo nnis 14

, Sargassum p/agiophyl lum 15

, Ascophy / I wn nodosum (Alg i fe rt ) Jr.,

Ulva fac tuco, Durl' illea potatorum, Sargassum lVightii 17,

Saragassum plagiophyllum and Padina pavonica 1x,

Sargassu m , Champia , Padina , Turbinaria , Helmin thocladia 1 ~ , Laminaria saccha rina, Funts ser­ratus, Fucus vesiculosus n , Ptemc/adia and Ecklonia

radiata 20, Padina tetras tomati ca a nd Sargassum

tenerimwn 21.

Method I - Challen and Hemingway Ll have de­

scribed the method where in two samples of co mmercial seaweed meal, one derived from Ascophylfu111 nodosum and another derived from Funts vesiculosus were used to prepare extract accord ing to the following method :

The powder was mixed with distilled water and al­lowed to stand. The mixtu re was boiled. al lowed to stand for some time, then passed through a fi ne sieve to re-

move the solids and the liquor obtained was centrifuged . The solids from the sieve and centrifuge were pressed and the liquor obtained was mixed with the main liquor. The combi ned I iquors were then concentrated under re­duced pressure to yield a brown fluid . The percentage of total solids was determined and the ex tract diluted with suffic ient water to contain the same percentage o f tota l solids as the commerci al seaweed ex tract. The ex trac t

of dry seaweed was further diluted when required .

Method 2- The method is g iven by Bhosale et a/. 21

in whi ch c hopped Sargassum ten erimum or Padina tetrasomatica was boiled with di still ed water and then

filte red. The filtrate was taken as I 00 per cent concen­tration of the seaweed ex tract and from thi s d ifferen t concentrations were prepared using di still ed water.

Chemical Constituents of Seaweed Extract It has been already establi shed that the beneficial ef­

fect is due to the presence of trace e le ments and in par­ticular the growth hormone like substances such as cy­tok inin in seaweeds. T he chemical constituent for dif­ferent seaweed ex tract have been reported by vari ous workers 17

·225

. Simi larly the presence of natural cy tok i­nin in seaweed ex tract has also been already reported in Ecklonia maxima 23 and Ascophyllum nodosum 2u 1

.

Effect on Seed Germination and Seedling Growth The treatment of seaweed ex tract increased the seed

gennination.However, concentrati on plays an import ant role to impart desired effec ts. In hi gher concentrati on the respiratory activity was higher and the percentage germination was less. But when the concentration was such that the respiratory activity was on ly moderate ly inc reased the germination percentage also was in­creased20 . More rapid germination of rice seeds was ob­served when soaked in seaweed ex tract o f Phonnidiu111 fovea/arum 14

•

Venkatraman et al. 15 have experimented with the pre­pared extract from Smgassum p/agiophy //um and com­mercia l seaweed extract (SM3) and reported that liquid seaweed fe rti llzer promoted seed germ ination and en­hanced early seedling growth upto a concent ration of 0.75 per cem in black gram and upto a concentration of 1.5 per cent in green gram . The significant g rowth of the seedling of black gram and green gram have been re­ported when the seeds were soaked in 0.1 per cent and 0.05 per cent ·elution of seaweed extract Alg ife n 1r' . Mohan et a/ . 1 ~ prepared extracts from five se lected

380 JSCIINDRES VOL60MAY2001

seaweeds namely P(J(/ina, Sasrgassum , Turbinaria , Champia and Helminthocladia and carried out studies on the effect on germination of seed and seed ling growth in Cajanus CC(jan. They found that crude extracts ob­tained from brown seaweeds especially that of Sorgos­

sum and Padina were more effective when the seeds were soaked in ex tract for 24 h.

Results from seaweed research on citrus showed that many of the metabolic stimulations observed at the low rate of seaweed ex trac t were probably the indirect result of IAA (Indole Acetic Acid) induced growth 27

.

Effect on Yield

Aqueous ex tract from Sargassum ll"igh tii (Ag), when applied as foliar spray on cultivated race of Zizyphus nwuritiana plants before harvest of fruits, enhanced over­all growth of fruit s in terms of length , breadth and we igh t by 11.23 per cent, 9.2 per cent and 25.36 per cent ,re­specti ve ly, over the control 12

.

Three different trials with strawberries gave respec­tive increases in the yield over the control of 14.8, 3 1.9 and 28 .0 per cent. With the turnips the mean yield per root was: control 22 g, seaweed ex tract 27 g. Each of these differences were statistically significant2x.

The increase in the yield of cucumber has been re­corded to the tune of 4 1 per cent over the control _~ , while Booth 29 has reported the increased yield of potatoes by 20 per cent through the appli cati on of seaweed ex tract at I 0 ga l/ac.

The fi eld trial s using seaweed ex tract (S M3) carried out by Blunden4 indicated that banana bunches shot on an average 8.5 weeks earlier when seaweed ex trac t was given in the form of foliar spray. Application at 0.75 gal/ac gave the average bunch weight 17.69 kg as against the control ( 14.5 I kg), reg istering the increase in the yield by 22 per cent over control. The increased corn weight from five different blocks was in the range of 6.2 per cent to 29.44 per cent. It has also been reported that the yield of tomato increased by 20 percent after appli ­cat ion of seaweed extract at the rate of I ga l I ac.

The increase in the fresh and dry weight was observed in case of Vigna ungiulata L. ( Walp) when treated with o.25 per cent of liquid seaweed fertilizer obtained from green seaweed Ulva lactuca. It also enhanced the accu­mulation of total nitrogen and phosphoru s 17

From the results, it is likely that the increased yie ld can be attributed to the cy tokinin like substances present in the seaweed ex tracts . However the effect of increased

yield may well be an ex press ion of the effec ts consid­ered elsewhere (i.e. res istance to di seases, root develop­ment). The effec t of minerals supplied in situation or marginal defic iencies shou ld also be considered ' ·

Effect on Shelf-life and Storage of Produce It has been reported that seaweed sprays appli ed to

peach trees generall y resu lted in greater she lf -life or treated fruit s. After 2 1 cl , more than 50 per cent of un­treated peaches were unmarketable, compared to less than 20 per cent of the fruit receiving seaweed sprays. Earlier applications, begining wi th fu ll bloom gave bet­ter resul ts than did sprays during the last of the growing season. Seaweed applied to peach trees has no appre­ciable effect on pH , firmness , ~o lub l e so lids or total titrabl e acidity ' 0

.

Similar results were observed when peaches sprayed with seaweed ex tract before harvest k pt longer. Six­teen days after harves t it was observed that 32.2 per cen t of the controls were rotten, compared wi th onl y 14.7 per cent of the fruit from treated trees .1 . Applying two foliar sprays of seaweed (DSWE Algifert) extract to Cox·s orange apple trees two weeks and four weeks before har­vest led to statist icall y significant increase in she lf- li fe as measured by visual appearance and the hardness of the flesh. The spray ing did not change the nutriti ve va lue est imated through sugar conten t, ac idity and soluble dry su bstance31

•

Peepers harves ted from each block were kept in the darkness at 23°C for 8 d by which time all the control fruits were unmarketable clue to softening and co lour changes but those from seaweed extract (0.5 gal/ac and I gal/ac) treated plants were still marketable4

.

Blunden et o/. 10 have reported that the shelf -life of produce was significantl y increased by immersion in seaweed extract. They have in ves tigated the effects or post harvest dipping of fruit s in seaweed ex tract sol u­ti ons of known cytokinin activity and fo und no signifi ­cant effect on ripening time as a result of clipping aub­ergines, avocados, and pears in either diluted seaweed ex tract or in aqueous sol utions of kinetin. However, ba­nanas showed a signifi cant increase in the ripening rate after being dipped in diluted seaweed ex tract or in an aqueous solution of kinetin . Mature gree n fruit s of man­goes when dipped in SMJ with an activity equiva len t to 7.5 ppm kinet in gave significa nt results but mos t effec tive treatment was found to be immers ion in marinure at 30 ppm kinetin- equivalen ts. The marked reducti on in the" degreening" of li mes were noted when

ZODAPE : SEAWEEDS AS A BIOFERTILIZER 3HI

immersed in diluted seaweed extracts for I h and which is of potential economic va lue. Immers ing capsicum in seaweed ex tract solutions with a kinetin equi va lent of 15,7.5 and 2.5 ppm, caused a significant reducti on in the reddening.

Seaweed ex tract can also be used on fl owers. Trials at Clemson University with Poinsettias have shown that there is an increase in the number, weight of the fl owers increased as much as 27 per cent and quality of the fl ower

with low concentration26•

Effect of Seaweed Extract on Resistance of Plants Soon after the seaweed extract came into use, it was

noticed that it virtually e liminated "black spot" from roses. In some breeding experiments with the green peach potato aphid on turnip leaves, it was found that there was much less mildew on leaves which had been sprayed with a seaweed extract. It has been reported that mildew was much less prevalent on me lons, which had been sprayed with seaweed extract. It has also been shown to

reduce the incidence of brown rot of peaches from 3.7 per cent to 1.5 per cent . It was observed from the ex­periment undertaken to inves tigate claims by growers that seaweed extract seemed to reduce the incidence of Botrytis infect ion in strawberries29

.

Stepheson2x has observed that the hydrolysed seaweed greatly reduced the incidence of damping off. The mean number of tomato seedlings to reach fourth leaf stage without damping off was 45 per cent in the control and 90 per cent in those treated with maxicrop . Overhead watering of plants with I : 120 dilution of seaweed ex­tract (Maxicrop standard) each week reduced the inci­dence of infected fruit to 4.6 per cent compared with 22.5 per cent for the control plants. It was further re­oorted that when aphids were given the choice of treated md untreated sugar beet leaves of the same physiologi­:al age the majority of the alate aphids always went to he control s . The mean percentage distribution of young )lack bean aphids over a 5 h period was 20 per cent 'rom maxicrop treated vs 83 per cent from control. The ;ignificant reduction in the population of red spider mite md aphid was reported by the app licat ion of seaweed ~x tract on chrysanthemum. Seaweed ex tract have been ;hown to e nsure improved res istance o f pla nts to mfavourabl e conditions of environment ( fros t an d lrought) and reduce incidence of fun gal , in sec t, and 1ematode attack 9

.

It is now well known that substances with growth regu­ating properties also have an inhibitory effec t on di s-

ease and in sect pests . Since seaweed extract contain s growth-promoting substances it now seems log ical that they should also inhibit the growth of insect pests and fungal di seases 1 ~ .

Seaweed Extract As A Soil Improver The modern trends of seaweeds utili zation as so il ma­

nure were set in 195 1 in the European countries and the seaweeds were used along with the farm yard manure as

so il conditioner in those countries 32. Since seaweed fer­

tili zer supply trace e lements, it is particularly very use­ful on alkaline so il s where deficiency di seases are com­mon 14 and help in improving the so il condition.

It has been already mentioned that seaweeds are not only used in the form of liquid, but all forms of seaweed have for centuries been applied to the land as a fertili ze r. Liquid seaweed application results in improvement in plant growth and so il texture . Improved soil structure is in variably associated with better aerati on, enhanced ni­

trogen fixation, and generalized ra ised proliferati on of so il organisms. Capillary action is a lso increased and as a result, root system of plant are st imul ated into furth er growth. The application appears to bring about mob ili ­zation of certain trace e lements in soi ls where these tend to be in unavailab le form33

.

Thivy 11 has reported that brown seaweeds such as Sargassum are valuable as manure, since they contain some of the soluble a lginates (polyuronides) which serves as soil conditioners and alginic acid which acce l­erate decomposit ion of organic matter by bac teria . Sea­weed manure steps up bacterial populations inc luding nitrogen fixers. The waste products excreted by soi l bac­teria contain other polyuronides that serve as additional soil conditioners. Seaweed manure can rectify unusual deficiencies and defects of the soil and has other advan­tages also. A remarkable capac ity for retaining water is noted in Sargassum manure.

Soils that contain large amounts of clay and only mini­mum of organic material are not porous and are said to lack crumb structure. Humic acid, and to a greater ex­tent soluble alginates in seaweed, bind partic les of c lay into larger aggregates or create cnunb structure by com­bining chemically with metallic radica ls present in the soil. They bring about aggregation of soi l particles. ln the case of soluble alg i nates, each metallic radica ls com­bine with two or more a lg inate molecules to form a po ly­mer or large molecule wi th branched chai ns. The po ly­mers are responsible for the formation of crumb struc­ture.

382 J SCI IND RES VOL 60 MAY 200 I

Acknowledgement

Author expresses his sincere thanks to Dr Rangarajan for valuable guidance and the Director for his kind per­mission to publi sh thi s paper.

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