Bio-pesticides and Bio-fertilizers for sustainable sericulture

Dr. Dayakar Yadav 

Dr. Dayakar Yadav is senior scientist with Central Silk Board (CSB), India. After obtaining PhD in Mycology and Plant Pathology in 1980, he had a long and fruitful research career with reputed organizations in India such as Karnataka State Forest Department, University of Agricultural Sciences, Bangalore, Karnataka State Sericulture Research and Development Institute, Central Sericulture Germplasm Research Institute (CSB), Central Sericultural Research & Training Institute, Central Silk Board. He has published more than 60 research papers in reputed journals and attended overseas training programs in Japan and China.

Introduction

The 20^th century has witnessed a slow but steady emergence of bio-pesticides and bio-fertilizers as potential supplementary and environment friendly inputs to their chemical counterparts. With the documentation of nearly 2500 bioactive plant species, over 1000 protozoa pathogenic to insects, 700 species of invertebrates and an array of other micro and macro-bioagents; their role in future crop protection cannot be ignored. Likewise; bio-inoculants or bio-fertilizers, primarily the nitrogen fixers and the phosphate solubilizers, hold vast potential in meeting plant nutrient requirements while minimizing the use of chemical fertilizers. Furthermore, successful exploitation of genetic engineering technology (metagenomics) to incorporate non-native pesticide producing genes into crop plants has added another dimension to the potential use of these inputs in agriculture. Currently, Asia-Pacific countries are the leading advocates of bio-pesticides and bio-fertilizers for sustainable agriculture.

Agriculture practices and its impact on the earth

In the beginning of 21^st century, agriculture accounts for the major share of human use of land. Pasture and crops alone taking up 37 percent of the earth's land area and over two-thirds of human water use is for agriculture (in case of Asia it is four-fifths). Crop and livestock production have a profound effect on the wider environment. They are the main source of water pollution by nitrates, phosphates and pesticides, also the major source of the greenhouse gases methane and nitrous oxide and contribute on a massive scale to other types of air and water pollution. The overall external costs of all three sectors can be considerable. However, the long-term consequences of these processes are difficult to quantify.  If more sustainable production methods are used, the negative impacts of agriculture on the environment can be attenuated. Indeed, in some cases agriculture can play an important role in reversing them, for example by storing carbon in soils (i.e., organic carbon) enhancing the infiltration of water through bio-fertilizers and bio-pesticides.

Role of Fertilizers and pesticides in sustainable environment

Concern has also grown in recent years that the use of fertilizers, particularly inorganic fertilizers, can lead to serious environmental consequences. Environmental contamination of this type, however, is largely a problem in the developed world and a few regions of the developing world. As fertilizers make up a small share of the total production costs in many developed countries, farmers often apply fertilizers in excess of recommended levels in order to ensure high yields. Over application of inorganic and organic fertilizers is estimated to have boosted nutrient capacity in the soil by about 2000 kg of nitrogen, 700 kg of phosphorus, and 1000 kg of potassium per ha of arable land in Europe and North America during the past 30 years. Such oversupply of nutrients can lead to environmental contamination, which often has negative consequences for humans and animals.

Pollution of groundwater by agricultural chemicals and wastes is a major issue in almost all developed countries, its use efficiency has to be improved or use alternate source of manures. Though the current use in many developing countries is very inefficient, China which is the world's largest consumer of nitrogen fertilizer, up to half the nitrogen applied is lost by volatilization and another 5 to 10 percent by leaching. Nitrogen synthetic fertilizers are considered the most detrimental to the environment, causing leaching and runoff that freshwater habitats and wells. Nitrogen synthetic fertilizers are a major contributor to increased N2O emissions, which are 300 times more potent than CO2 as greenhouse gas, which is ominous for global warming as synthetic fertilizer use is forecasted to increase roughly 2.5 times by mid-century.

Insecticides, herbicides and fungicides are also applied heavily in many developed and developing countries, thus polluting the fresh water resources with toxic and other poisons that affect humans and many forms of wildlife. Pesticides also reduce biodiversity by destroying weeds and insects and hence the food species of birds and other animals.

Over the past 3 to 4 decades, usage of insecticides show signs of decline, both in developed countries especially France, Germany and the United Kingdom and in a few developing countries, such as India. In contrast, herbicide use continued to rise in most countries. As concern about pollution and the loss of biodiversity grows, future use of pesticides may grow more slowly than in the past. The future is likely to see increase use of "bio- pesticides and ecological methods of disease and pest control.

A pesticide of biological origin like viruses, bacteria, pheromones, plant or animal compounds is known as bio-pesticide. They are highly specific affecting only the targeted pest or closely related pests and do not harm humans or beneficial organisms while chemical pesticides are broad spectrum known to affect non-target organisms including predators and parasites as well as humans. The striking feature of bio-pesticides is environment friendliness and easy biodegradability, thereby resulting in lower pesticide residues and largely avoiding pollution problems associated with chemical pesticides. Further, use of bio-pesticides as a component of Integrated Pest Management (IPM) program can greatly decrease the use of conventional (chemical) pesticides, while achieving almost the same level of crop yield. However, effective use of bio-pesticides demands understanding of a great deal about managing pests especially by the end users.

In terms of production and commercialization also bio-pesticides have an edge over chemical pesticides like low research expenditure, faster rate of product development as well as flexible registration process. The global weighed average consumption level of bio-pesticides is approximately 1 kg/ha. With the global organic farming area comprising about 24 million hectares, global bio-pesticide consumption is thus estimated at about 24 million kg. The bio-pesticide market is growing very rapidly, in 2005 it accounted for about 2.5% of the total pesticide market, which was merely 0.2% during 2000. This share is expected to a level of about 4.2% by 2010 while the market value is estimated to reach more than US$ 1 billion (Source: BCC research). However, the overall growth rate of bio-pesticides is estimated to be about 10% per annum for the next 5 years.

Research experiences towards sustainable Sericulture development

The Sericulture-based Integrated Farming System Management (IFSM), Integrated Nutrient Management (INM) and Integrated Pest Management (IPM) programmes are farmer-centered and farmer-participatory aimed at promotion of eco-friendly approaches for sustaining productivity and also optimization of resources utilization.  These two projects were implemented in Andhra Pradesh, Tamilnadu and Karnataka states during 2002 to 2007. Under these projects, a number of technologies were evolved towards sustainable sericulture which can be translated to other crops.  The technologies developed were of integrated nature and cost effective serving the purpose of eco-friendliness, sustainable development and reduction in cost of production in silk.

More poor people depend upon sericulture for their livelihood. Poverty alleviation necessarily demands increased sericulture productivity, which is a largely a function of 'technology'. Absence of technological intervention would lead to increased depletion of natural resource base. Poverty subverts efforts to introduce sustained sericulture in ways detrimental to the environment. This would lead to a decline in sericulture production potential, and sustaining capacity of sericulture would also decrease. With the ever-increasing population poverty gets perpetuated widely and deeply, furthering environmental degradation.

'Silk and Milk'

Karnataka, amply termed as silk bowl of India, from three southern states around 1.4 lakh ha. of mulberry, wherein approximately 42 lakh MT of annual production is estimated. The wastage (bed refusal) of silkworm rearing activity is used as cattle feed; silkworm litter or faucal matter as organic manure; pupae for extraction of oil / feed for poultry etc. One hectare of mulberry garden can produce about 25- 28 tones of mulberry leaf year from which 1200- 1500 kg of cocoons are produced. During this activity, about 20% (750-10000 kg/ha/crop) of leaf and/or twigs which is considered as bed refusal is fit to use as fodder for cattle. Bed refusal (uneaten leaves and tender stump) produced during rearing is effectively used by the farmers to rear cattle. It constitutes about 50% of the fodder requirement of cattle. Further, the bed refusal and tender stumps produced out of one hectare of mulberry is almost sufficient for 7 -8 cows. Apart from this, around 5% of the mulberry, which will either be soiled or unfit due to over maturity, can be used as fodder to the cattle. Rearing of eight cattle along with silkworm rearing will in turn meets the FYM requirement of one hectare of mulberry plantation. Valuable FYM will also be produced at the farm itself. Mulberry leaf stalk/stump forms the low cost/no cost alternative fodder for the cattle. By and large it is important that dairy animals have good appetite and mulberry leaf is palatable and the animal eats it very well.

Soil Health

Proper soil management without impairing soil health is the prerequisite for achieving higher productivity in sericulture. The situation has created a renewed interest in the biological transformation of sericultural farm wastes including all organic wastes into valuable manures which can be profitably used in the mulberry fields for the cost-effective production of mulberry leaves. This nutrient-rich compost is a better supplement for farmyard manure, the cost of which is escalating day by day due to shortage of cattle dung.

Integrated Plant Nutrient Supply

Azotobacter

Heavy use of nitrogen started up showing in increased nitrate concentration in underground waters in states like Maharashtra and Punjab. Due to these alarming signals, Integrated Plant Nutrient Supply (IPNS) has become a sustainability concept. IPNS involves meeting a part of the nutrient need of crops by organic manures, crop residue, green manures, dual-purpose legumes and bio-fertilizers. The need for IPNS was suggested by long-term fertilizer experiments on wheat. Application of N alone reduced the yield of wheat to zero after 13 years. Application of P along with N extended it to 22 years but in NPK plot some yield was obtained even after 22 years. 

However, plots receiving a part or all nutrients through FYM not only maintained but also recorded a gradual increase in crop yield over years. Combined application of FYM and inorganic fertilizer was the best.

Bio-fertilizers: In recent years, use of bio-fertilizers holds much promise to improve the yield of crops. Bio-fertilizers sustain soil fertility resulting in increased crop yield without causing any environmental, water, or soil hazards. Out of many microorganisms, which are identified as biofertilizers, Azotobacter chroococcum, Azospirillum brasilense, A. lipoferum, Phosphorus Solubilizing Bacteria (PSB) and Vesicular Arbuscular Mycorrhizae (VAM) have proved to be beneficial in mulberry nutrition.

VAM

VAM

VAM in root cell

VAM fungi in association with higher plants play an important role in phosphorus nutrition and increase plant growth and yield. Application of phosphorus @ 30 kg/ha/year as Mussorie Rock Phosphate (MRP) with Glomus mossae inoculation significantly increased the cocoon yield. Moreover, cocoon quality due to application of phosphorus @ 30 kg/ha/year in the form of MRP with G. mossae and G fasciculatum inoculation was statistically at par with plant receiving full dose of phosphorus (@ 120kg/ha/year) without VAM inoculation. Thus curtailing 75% of phosphorus application in mulberry cultivation and reduce of cost of cultivation. Combined inoculation of VAM with diazotropic Azospirillum  brasileAdd captionnse yields more mulberry leaf biomass with high nutrient level than inoculation of individual organisms.

Phosphobacterium

Phospho bacterium

Similarly to VAM and PSM the Phosphobacterium when applied to the soil, it solubilizes the insoluble phosphorus in the soil to make it available to the plants for absorption. This helps in efficient use of Phosphorus and save application of Phosphorus. Many of the cultivated soils contain high amount of total phosphorus but availability is limited due to insoluble forms. Only water-soluble phosphorus is useful for the crop plants. Many bacteria are capable of solubilising insoluble soil phosphorus, of which the role played by Phosphorus Solubilizing Bacteria - Bacilus megatherium var phosphaticum  is significant.

Organic Manures 

With a view to minimize the use of chemical fertilizers, farmers are able to produce different organic manures and apply as part of IPN system. Recycling of Sericultural Farm Wastes as Compost: It was established that various composts prepared out of sericulture farm wastes on mulberry revealed that application of compost prepared out of silkworm rearing wastes @ 20 MT per hectare per year or application of recommended dose of farm yard manure (20 MT per hectare per year) and chemical fertilizers also produced same quantity of leaf as against the conventional farm yard manure and chemical fertilizers. Two years crop data showed significant increase in leaf yield (61.5 tonne/ha) with application of compost @ 4.5 tonne/ha/year in conjunction with full dose of chemical fertilizers. Compost application @ 4.5 MT/ha/year (Prepared from silkworm rearing waste mixed with biogas spent slurry) + 300: 120: 120 NPK kg/ha/year produced a leaf yield was 57.8 tonne /ha/year. The study indicates that the compost and vermi-compost produced out of sericulture wastes are qualitatively superior over FYM.

Fortification of Vermi-compost

Fortifications carried out by blending the sericultural wastes with microbial inoculum - Azotobacter, phosphate solubilizing microorganisms (PSM) and add rock phosphate and single super phosphate. The process of vermi-composting of sericultural wastes (200 kg/trench) was carried out by introducing a mixed culture of juvenile earthworms Eudrilus eugeniae, Eisenia fetida and Perionyx excavatus @ 500 grams per trench. The chemical analysis of vermi-compost had organic carbon content ranged from 9.15 to 10.65%. NPK contents (2.45%; 1.75% and 1.17% respectively) was maximum in Semi decomposed sericultural farm wastes fortified with both S.S.P. and R.P. @ 12.5 kg each/MT of wastes and by inoculating with Azotobacter and P.S.M. Each cycle of vermi-composting was completed in 60 days compared to all other treatments.

Green Manure Compost

A large number of leguminous crops are used for green manuring in South India. Daincha (Sesbania aculeata), sunnhemp (Crotalaria juncea), wild indigo  (Tephrosia purpurea), indigo   (Indigofera tinctoria) and Pillipesara (Phaseolus trilobus) are the most popular crops with farmers. A number of other leguminous crops like cowpea, lablab, red gram; Crotalaria striata, etc., are also to able to fix atmospheric nitrogen and do not necessarily depend on the nitrogen in the soil. The phosphorus present in green manure is in organic combination and becomes available for use by mulberry in the succeeding harvests. Green manure decomposes easily without leaving much of the residue in the soil. The amount of humus added to the stock already in the soil is negligible. In this respect it is different from farm yard manure. If, however, the green manure crop is allowed to mature and is ploughed in, it decomposes slowly and some humus is added to the soil.

Pesticides of Plant Origin

One of the viable alternatives to chemical pesticides is the development and use of better botanical pesticides, which are environmentally safe, effective against pests, easy, and economic. As plants and insects have co-evolved over millions of years, they have accumulated specific secondary plant chemicals (SPCs) to counteract the insect damage. These bioactive chemicals include insecticides, anti-feedants, Insect Growth Regulators (IGRs), juvenile hormones, ecdysones, repellents, attractants, arrest ants, etc. Hence, plants are thought to be an important alternative source for chemical pesticides. Over the years more than 6000 species of plants have been screened and nearly 2400 plants belonging to 235 families were found to possess significant biological activity against insect pests.

Towards sustainable environment, health and development certain innovative technologies have been developed recently to control root rot diseases caused by Rhizoctonia bataticola (anamorph of Macrophomina phaseolina) on crops like mulberry, carrot, banana etc., it is well known that the soil borne pathogens cause severe damage to crops especially in tropical belt where the environment is suitable for the pathogen to survive and damage the host plants and complete their life cycle. A novel method was developed using plant bio-formulations, which are anti-fungistatic, and inhibitor of root rot fungal pathogen in soil. Some of the plant species, which are known to inhibit growth of fungus, like Guizotia abyssinica (L. f.) Cass. (ramtilla), Azadirachta indica A. Juss. (neem), Brassica juncea (L.) Czern. (India mustard) are inhibitors of fungal growth in soil up to 93%. A new formulation was developed ‘Navinya’ an eco-friendly plant based formulation, which was tested for its efficiency on host plants at hot spot areas where root rot is a major cause of damage to mulberry plantation. The formulation was effective in inhibiting the fungal pathogen in its spread and inhibits the growth and makes the plant recover, to support the host plant small quantity (8%) growth promoting substances like succinic acid, boric acid is added along with inorganic chemicals (12%) in the formulation.  Among the 15 villages participated in the trials all found satisfied with the control of the disease in mulberry plantations.