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There is increasing interest in use of‘alternative’soil amendments in agriculture, but the wide range of resourcesand products available differ greatly in their potential to overcome soil constraints and improve nutrient useefficiency. The three main types of biological amendments can be categorised as biostimulants, organicamendments and microbial inoculants. Many have potential to influence biological, chemical and physicalconditions of soil, but most are not well researched or easily used in agriculture. The main exception is legumeinoculants, which are very well researched and contribute enormously to agricultural productivity when le-gumes are incorporated into farming systems. Biostimulants include amino acids, chitosan, seaweed extracts andhumic substances. Organic amendments include manures, composts, compost derivatives and biochars.Microbial inoculants include specific bacterial inoculants for legumes, and less specialised rhizosphere bacteria,arbuscular mycorrhizal fungi, ectomycorrhizal fungi and a range of disease suppressing microorganisms. Somebiological amendments applied to soil may be more effective when used in combinations rather than singly.Furthermore, those used over longer periods may have potential for cumulative effects not captured when usedover shorter timeframes. Such differences in effectiveness would occur primarily where benefits involve mi-crobial interactions with chemical and physical soil processes leading to slow transformations within the soilmatrix that influence soil fertility and soil health. Similarly, addition of manures and composts may requireseveral years for any quantifiable increase in soil organic C. Although considerable knowledge of the modes ofaction of many biological amendments is available, their performance underfield conditions is usually less wellunderstood. The wide variety of natural and manufactured products available in most cases precludes adequatepeer-reviewed research to support claims about their effectiveness. This can lead to proliferation of un-substantiated assertions of efficacy. This review highlights the lack offield-scale evidence of benefits for manybiological amendments with potential to be used in agriculture. We propose complementary approaches of (i)laboratory- or glasshouse-scale research to understand modes of action, and (ii) targetedfield-scale participatoryresearch involving groups of farmers using on-farm trials as a forward pathway. Use of biological amendments toovercome soil constraints is expected to expand with intensification of agriculture and as a result of climatechange. Therefore, information that enables farmers to discriminate among products that have different levels ofeffectiveness is necessary, and on-farm participatory research should contribute to addressing this need.

Data collected on the commercial exploitation of seaweeds from the natural seaweed beds of Tamilnadu during 4 years period from 2000 to 2003 showed that the quantity of agarophytes viz. Gelidiella acerosa, Gracilaria edulis, G.crassa, G.foliifera and G.verrucosa varied from 965 to 15 18 tonnes (dry wt) and alginophytes Sargassum spp and Turbinaria spp from 1433 to 2285 tonnes (dry wt) per year. The commercial harvest of seaweeds in Gulf of Mannar and Palk Bay is recommended only during the peak growth period of the algae from July 1 August to January. The harvest of commercially important seaweeds in a rational way from other parts of Indian coast, Lakshadweep and Andaman-Nicobar Islands is suggested. The need for large scale cultivation of agarophytes to augment the resources and uninterrupted supply of raw materials to the seaweed industries is emphasised.

Uncle Wally Ito is passionate about limu, or seaweed. He says limu has always been an integral part of Hawaiian culture, with uses in food, medicine, and religious ceremonies. In a traditional Hawaiian diet, limu was the third component of a nutritionally balanced diet along with fish and poi, providing an important source of minerals and vitamins. Limu, such as wawae‘iole (Codium edule), manauea (Gracilaria coronopifolia), ele‘ele (Ulva prolifera), kohu (Asparagopsis taxiformis), and līpoa (Dictyopteris plagiogramma), are still a common ingredient in many Hawaiian dishes, adding flavor and spice to poke and stews. “At one time there were countless diferent limu that were being consumed in Hawai‘i,” Uncle Wally says. “Today, we would be hard pressed to get a list of 20. So we’ve lost that knowledge of many kinds of limu.”

Culture of seaweeds is practiced since ages in countries such as Japan, Ctiina and Korea. Seaweed cultivation is an industry in Japan as a part-time avocation for land farmers and fishermen. The seaweeds cultured mainly in these countries are Porphyra, Undaria, Laminaria, Enteromorpha and Monostroma. In India seaweed culture is yet to develop on commercial lines. While the demand for these seaweeds is for food purposes in foreign countries, their demand in India is for the extraction of two phytochemicals namely agar-agar and algin. In recent years many factories manufaauring these chemicals have come up in India as a consequence of which the demand for the agarophytes and alginophytes has gone up. In order to maintain a continuous supply of this raw material to the industry, methods to augment the supplies through culture practices have to be developed.

In recent years the Central Marine Fisheries Research Institute has been engaged in the cultivation of several economically important seaweeds such as Sargassum wightii, Twbinaria spp., Gracilaria edulis, G. corticata and Gelidiella acerosa which indicated great scope for cultivation. The production rate has been found to be 4.4 kg/m' in the case of G. edulis and 3 kg/m* in the case of G. acerosa in about 80 days for 0.30 kg and 1 kg of seed material introduced respectively. In the case of alginophytes the growth was not encouraging. These culture experiments were conducted by introducing small fragments of the seaweed into the twists of the coir ropes fabricated in the form of a S x 2 m net and tied to fixed poles in inshore waters. In the case of G. acerosa, the substratum along with the plant fragments was tied to the ropes.

The agarophytes thus grown can be processed further for extraction of agar-agar. The extraction could be done by a simple cottage industry method not involving any costly equipment. In the case of Gelidiella agar, freezing and thawing are required to remove the insoluble chemicals. A total of 90 tonnes of G. edulis can be obtained from 3 harvests in a year from a hectare area.