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By Biswajit Pramanick (Asst. Professor, Department of Agronomy, Bidhan Chandra Krishi Viswavidyalaya, West Bengal)

Co-authors: Koushik Brahmachari,S.T.Zodape,Arup Ghosh

Looking behind before forward looking

In the early 60’s it was a very urgent surge for the agricultural scientists to give an immense push on the so called package of practices to ensure the food security for the ever escalating population of the nation. Thus a phenomenon like green revolution was must for the entire nation at that time. But during post green revolution era, unsystematic exploitation of chemical fertilizers, pesticides, herbicides etc put the entire environment and the overall ecological balance in danger. Fertilizers and pesticides both have definite pros and cons associated with their use. Both types of chemical tend to increase yields and thus make a significant difference in food production. On the other hand, both of them can cause water pollution when erosion carries the chemicals off of the farms along with eroded soils after each rainfall. There is also concern by some authorities that pesticides pose a risk, not only to non-target animal and plant species, but to human being as well. The downside of fertilizers is that some portion inevitably washes into waterways along with eroded sediments.

This nonpoint source runoff occurs nationwide and the nitrogen fertilizer finds its way into rivers, lakes and the ocean where it causes eutrophication and “dead zones” that kill aquatic life. Eutrophication is a process whereby nitrogen feeds an algal bloom; but when the short-lived algae die, decomposing bacteria consume most of the available oxygen and thus suffocating the aquatic life. Additionally, use of artificial fertilizers in place of animal or ‘green’ manure eventually can deplete soils of organic matter by making them lose their ability to hold water and more subject to erosion. Runoff of synthetic fertilizer can enter the waterways, causing water to be polluted and to lose oxygen. Over time, chemical fertilizers can degrade the quality of the soil by building up toxins or leaching away natural nutrients, making the soil unfit for growing plants. Using too much fertilizer can damage plants by chemical burning of roots and leaves. If we grow edible crops, synthetic fertilizers may contain unnecessary even sometimes harmful chemicals that will end up in our food. According to the National Institute of Environmental Health Sciences, pesticides have as yet incompletely understood effects on humans. Most people are exposed to a certain level of pesticides. Farmers who experience routine exposure to pesticides have exhibited neurological symptoms such as headache and hand tremors. Children, in particular, may be more susceptible to negative effects resulting from pesticide exposure. Pesticide runoff can have devastating effects on non-target organisms as well. For example, roundup, a widely popular herbicide used in agriculture, is highly toxic to fish and amphibians. The National Coalition for Pesticide-Free Lawns says, “Of 30 commonly used lawn pesticides, 19 are linked with cancer or carcinogenicity, 13 are linked with birth defects, 21 with reproductive effects, 26 with liver or kidney damage, 15 with neurotoxicity, and 11 with disruption of the endocrine system.”

It is a cruel reality that developing countries like India accounts for less than 30% of global pesticide consumption. The vast majority of pesticide poisonings occurs in developing countries. In India agro-chemicals account for as much as 25% of all occupational injuries in the agricultural sector and 15% of all fatal injuries. 69.4% pesticides are used in agrarian sector of India whereas in case of public health 30.6% pesticides are used. The information on crop wise pesticide consumption in India reveals that consumption of pesticide is the maximum in cotton (44.5%) followed by paddy (22.8%), sorghum (8.9%), vegetables (7%), wheat (6.4%), pulses (2.8%) and others (7.6%). The ill impacts of excessive pesticide uses are the contamination of the environment, soil and ground water causing serious human health hazards vis-à-vis narrow nutrient holding capacity, severe micronutrient deficiency and sharp declination in carbon stock of soil. All these things ultimately offer directly or indirectly more and more crucial problems to the environment ultimately acting as some of the important agents in changing the climate as a whole. So, in the perspective of global climate change it can be uttered that it is the high time for reshaping our present package of practices in agriculture and introducing some alternative approaches to mitigate the hectic hazards of changed climate vis-à-vis sustaining the food security. One such approach is the use of biostimulants, which can enhance the effectiveness of conventional mineral fertilizers. Disadvantages of chemical fertilizers are going to compel the farmers to turn towards organic manures. To meet increasing demand of organic manures, among many viable options, one is the use of seaweed extracts as plant nutrient bearing fertilizer. The bioactive substances extracted from marine algae are used in agricultural and horticultural crops, and many beneficial effects may be attained in terms of enhancement of yield and quality. Liquid extracts obtained from seaweeds have recently gained importance as foliar sprays for many crops including various cereals, pulses and different vegetable species. Seaweed extracts have proven to accelerate the health and growth of plants. It supplies nitrogen, phosphorous, potassium as well as trace minerals like Zn, Mn, Mg, Fe, etc. It also contains natural plant growth substances like auxins, gibberlins and cytokinins. As it is an excellent source of almost all plant nutrients, it can substitute the conventional chemical fertilizers to some extent.

Some of such marine algal members are Kappaphycus, Laminaria, Ulva lactuca, Haliotis tuberculata, Porphyra, Macrocystis pyrifera, Alaria esculenta, Lithothamnion corallioides, Phymatolithon calcareum, Ecklonia, Agars, Fucus, Andaria, Bryopsis, Sargrassum, Aschophyllum, Macrosystis, Palmaria, Gracilaria, Manostama, Enteromorpha etc. The versatile utilities of these marine algae are making them popular day by day. Without mining into detail about the uses of these algae this article will be confined into their importance in the agrarian sector.

Causes behind the miracle effects of marine algae

Seaweed is amply rich in carbohydrates; the vital building block of plant body and a good food source of many beneficial micro-organisms. Unlike conventional forms of fertilizers, being a wealthy source of natural plant hormones viz. auxins, at least two gibberellins, endogenous cytokinins, betaines etc; various vitamins like B1 (thiamine), B2 (riboflavin), B12, vitamin E (tocopherol), vitamin K and other growth-promoting substances vitamin C (ascorbic acid) as well as pantothenic acid, folic acid and folinic acid etc; alginic acids; antibiotics; many macro nutrients and almost all micro nutrients in fully chelated form seaweed fertilizers are especially useful in organic farming. Chelating- a combination of mineral atom with organic molecules, makes micro elements available to the crops. Such chelating properties are possessed by the starches, sugars and carbohydrates in seaweed and seaweed products. For this reason, these components naturally combine with iron, cobalt, copper, manganese, zinc and other microelements present in seaweed. Thus these trace elements in seaweed and seaweed products do not settle out even in alkaline soils, but remain available to the crops which need them. Alginic acid is a soil conditioner and the remainders are plant conditioner. All these are found in fresh seaweed or dried seaweed meal as well as liquid seaweed extracts.useful in organic farming. Chelating- a combination of mineral atom with organic molecules, makes microelements available to the crops. Such chelating properties are possessed by the starches, sugars and carbohydrates in seaweed and seaweed products. For this reason, these components naturally combine with iron, cobalt, copper, manganese, zinc and other microelements present in seaweed. Thus these trace elements in seaweed and seaweed products do not settle out even in alkaline soils, but remain available to the crops which need them. Alginic acid is a soil conditioner and the remainders are plant conditioner. All these are found in fresh seaweed or dried seaweed meal as well as liquid seaweed extracts.

Spectacular fields where marine algal mass may function In soil management

Application of seaweed saps in the soil activate the soil microorganism viz. bacteria, fungi etc. and make the moisture more available to the plants. As alginic acid is a soil conditioner, therefore, its presence in seaweed and seaweed products improves the water holding capacity of soil and facilitates formation of crumb structure. Alginic acid in the seaweed combines with metallic radicals in the soil to form a polymer with immensely increased molecular weight of the type known as cross-linked. Virtually, the salts formed by alginic acids with soil metals swell when wet and retain moisture persistently. Alginates, the sponge-like starches found in seaweeds hold water droplets near the plant roots, making moisture available to them without drowning them.

TABLE- 1 : Chemical Composition Of Kappaphycus sap

[Data courtesy National Institute of Nutrition, Hyderabad, India (except growth hormone data generated by CSMCRI using quantitative MS-MS and LC-MS techniques)]

The application of seaweed meal in sloppy land can check the washing away of seedlings and nutrients into the ditch by improving the soil structure. Review says that in exceedingly dry period, cultivation of second crop is possible only with the field application of seaweed fertilizer, other fields dry out completely1. This incidence validates the water-retaining capability of seaweed. This in turn leads to better aeration and capillary activity resulting in stimulation of the root systems of plants for further growth and thus motivates the soil bacteria towards greater activity. Acceleration in bacterial activity through the soil application of seaweed meal results in the secretion of organic chemical substances like polyuronides by them that ultimately condition the soil thoroughly. Practically, polyuronides are chemically similar to the soil conditioner alginic acid that has soil-stabilizing properties. Thus seaweed fertilizer provides a couple of conditioning agents to the soil: alginic acid from the undecomposed seaweed in one hand and polyuronides from the soil bacterial secretion in another hand.

In crop production and crop health management

Application of seaweed saps have been revealed to be a successful technique to preserve proper plant health and improve the productivity without disturbing the overall ecological balance. It has been noticed that pre-sowing or pre-planting treated seeds or seed pieces will germinate effectively and rapidly resulting in robust root growth and vigorous seedling at early stage. Simultaneously, higher survival rate can also be achieved. Cuttings immersed in liquid seaweed solution produce profuse roots. Soaking plant roots in seaweed extract reduces transplant shock and expedites root growth. Frost and stress resistance, enhanced uptake of inorganic constituents from soil, reduction in storage losses of fruits, expansion of shelf life of fruits vis-à-vis vegetables and elongation of life of cut flowers are also some of the exclusive beneficial effects. The scientific causes behind these effects may be discussed in a nutshell. We have already discussed that seaweed fertilizers hold various phyto-hormones viz. auxins, gibberellins, cytokinins, betaines etc. They have both growth stimulating as well as retarding functions. Seaweed can play an important role in the production of the plant’s own auxins, because the enzymes formed with the help of trace elements from the liquid seaweed fertilizer play an important role in the formation of these auxins. The gibberellins plays the pivot role in simulating of roots, growth, flower initiation, fruit setting, fruit growth, fruit ripening, abscission and senescence when applied exogenously. The cytokinins available in liquid seaweed extract initiate and activate basic plant growth processes, enhances growth with bigger vigour through mobilising nutrients in the leaves. The betaines help the plants to fight against stress. They play vital role in the osmotic processes by helping the plants in increased water uptake even in dry condition and thus, as if, play the role of oasis in the desert. The antioxidants present in seaweed products effectively minimize rather prevent lipid oxidation in agricultural produces, retarding the development of toxic oxidation products, maintaining nutritional quality and prolonging the shelf life of such commodities. Another interesting incident is that seaweed sprays stimulate metabolic processes in the leaf and so help the plant to exploit leaf locked plant nutrients. Spraying with seaweed extracts may feed and stimulate the bacteria performing photosynthesis at the leaf surface to a considerable proportion and thus accelerate the process of photosynthesis. Moreover, plants treated with seaweed products develop a resistance to pests and diseases. Owing to the presence of ample amount of soil fungi and bacteria increased production of natural antibiotics occurs in the soil rich in organic matter. These antibiotics taking entry to the plants improve their disease resistance. Seaweed encourages this process and thus holds down the population of plant pathogens.

Some real stories

Field trials conducted by different universities including Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal in association with Central Salt and Marine Chemicals Research Institute, a sister institute of Council of Scientific and Industrial Research revealed that seaweed can produce amazing results in plants. Application of liquid seaweed extracts increased yield by 26%, 39%, 57%, 61% and 20% of rice2, greengram3, soyabean4, tomato5 and okra6 respectively. Superior yields after seaweed treatments were measured in watermelon7, wheat8, Potato9 and grape10. Besides, quality characters of different crops like cereals, pulses, oilseeds and tuber crops are largely influenced. It has also been found that use of seaweed as soil treatment substances results in strong and healthy growth vis-à-vis disease-resistance.

References

1. William Anthony Stephenson, Seaweed in Agriculture and Horticulture, 1968, pp 182, Faber “,” Faber, London.
2. M. P. Kavitha, V. Ganesaraja and V. K. Paulpandi, Agric. Sci. Digest, 28 (2), 127 – 129, 2008.
3. Biswajit Pramanick, Koushik Brahmachari and Arup Ghosh, Afr. J. Agric. Res, 8(13), 1180-1186, 2013.
4. S. S. Rathore, D. R. Chaudhary, G. N. Boricha, A. Ghosh, B. P. Bhatt, S. T. Zodape and J. S. Patolia, S. Afr. J. Bot, 75, 351-355, 2009.
5. S. T. Zodape, Abha Gupta, S. C. Bhandari, U. S. Rawat, D. R. Chaudhary, K. Eswaran and J. Chikara, J. Sci. Ind. Res, 70, 215-219, 2011.
6. S. T. Zodape, V. J. Kawarkhe, J. S. Patolia and A. D. Warade, J. Sci. Ind. Res, 67, 1115 – 1117, 2008.
7. A. M. R. Abdel-Mawgoud, A. S. Tantawy, M. M. Hafez and A. M. Hoda, J. Agri. Biol. Sci, 6(2), 161–186, 2010.
8. S. T. Zodape, S. Mukherjee, M. P. Reddy and D. R. Chaudhary, Int. J. Plant Prod, 3, 97-101, 2009.
9. M. E. Lopez-Mosquera and P. Pazos, Biol. Agric. Hort, 14, 199-206, 1997.
10. J. Norrie and J. P. Keathley, Acta. Horticul, 727, 243-247, 2006.