Sustainable Land Use In Agriculture Environmental Sciences

Concerns about sustainability in agricultural systems centres on the need to develop technologies and practices that are adopted to attain optimum income per unit of land and time, do not have adverse effects on environmental goods and services, are accessible to and effective for farmers, and lead to improvements in food productivity and yield per drop of water. New approaches are needed that will integrate biological and ecological processes into food production, minimize the use of those non-renewable inputs that cause harm to the environment or to the health of farmers and consumers. Assured and continued agricultural yields, free of pesticidal residues, can be achieved by the adoption of organic farming with additional benefits of environmental and economic sustainability. Organic farming supplies not only the soil with nutrients, but improves the soil structure and induces useful microbiological processes, therefore, has vital importance on the preservation of soil fertility.

Use of chemical fertilizers in agriculture enhances yields but also undermines the quality of life through possible contamination of soil, water and air and even the final products that retain their residues.

1. Introduction

For a long time plants have played very important role for human life. Almost all essential minerals and organic nutrients to humans are provided via agricultural production (Wang et al., 2008). Chemical fertilizers and synthetic pesticides helped in increasing the yield of food crops but had adverse effects on the micro flora and fauna of the soil. To revive the good old agricultural practices and get rid of chemical fertilizers and pesticides which have ruined natural resources and soil micro organisms in the last few decades, hundreds of farmers have switched over to organic farming (Deccan Chronicle, 2010). The term "organic farming" was coined in the second half of the 20th century to qualify the food production system that has nourished the world for 10,000 years. Organic agriculture is a sustainable form of production. It promotes and enhances biodiversity, biological cycles and soil biological activity. It is based on minimal use of off-farm inputs and on methods that restore, maintain and enhance ecological harmony. Organic farming is defined worldwide as farming without the addition of artificial chemicals. 'Organic farming' is a term defined by International Federation of Organic Agricultural Movements (IFOAM) standards and all organic food production and processing is governed by a strict set of standards and guidelines. Organic farming does not use synthetic chemical pesticides, herbicides and fertilizers, relying instead on developing a healthy, fertile soil and sound crop rotations. The organic agriculture practices rely to the maximum extent on mulching, crop residues, animal wastes, crop rotations, green leaf manures, composting, bio-gas slurry, biofertilizers, off-farm organic wastes, press mud etc. (Purohit and Gehlot, 2006) and organic recycling to supply plant nutrient and adopt biological control methods to control pests, diseases and weeds. In this way, the farm remains biologically balanced, with a wide variety of beneficial insects and other organisms to act as natural predators for crop pests and a soil full of micro organisms and earthworms to maintain its vitality (IFOAM, 2009). It is important that sufficient plant nutrient is present in soil. Therefore, organic manure plays a direct role in plant growth as a source of all necessary macro- and micronutrients in available forms during mineralization, improving the physical and physiological properties of soils (Abou El-Magd et al., 2006). It is believed that organically grown crops are healthier and contain more minerals and vitamins than that of the conventional counterparts (Warman and Havard, 1997; Worthington, 2001).

Pesticide and other chemical residues in food and an overall reduced quality of food have led to a marked increase in various diseases, mainly various forms of cancer and reduced bodily immunity. This immense commercialization of agriculture has also had a very negative effect on the environment. The use of pesticides has led to enormous levels of chemical buildup in our environment, in soil, water, air, in animals and even in our own bodies. Fertilizers have a short-term effect on productivity but a longer-term negative effect on the environment where they remain for years after leaching and running off, contaminating ground water and water bodies. The use of hybrid seeds and the practice of monoculture have led to a severe threat to local and indigenous varieties, whose germplasm can be lost forever (Gujaral, 2006). It is a method of agricultural production that is environmentally friendly, requiring high standards of animal welfare with health benefits for people. Organic farming recognizes that human health is directly connected to the health of the food we eat and, ultimately, the health of the soil. Organic agriculture both relies on the vast knowledge and skills of farmers and on modern research to provide innovative new technologies. In organic farming serious crop damages due to weeds, pests, diseases, and pathogens can be prevented by using different agents of natural sources such as Brassica green manure, mustard meal, neem and Pyrethrum extracts etc. (Boydston and Hang, 1995; Brown and Morra, 1997) and biocontrol agents (for example ladybirds against aphids). There are various aspects affecting decision to convert to organic farming (Fig. 1).

The changeover from inorganic to organic farming is to be carried out only systematically and carefully. Organic farming can be adopted by decreasing the dose of inorganic fertilizers rather than an immediate removal and adopting organic farming practices timely and correctly. Organic manure has to be prepared which leads to environment friendly methods of organic waste disposal. Organic farming will reduce environmental pollution, toxic effects due to use of pesticides and minerals and problems of biodiversity conservation.

A large number of terms are used as an alternative to organic farming. These are: biological, ecological, bio-dynamic, organic and natural agriculture. Organic farming envisages a comprehensive management approach to improve the health of underlying productivity of the soil. In a healthy soil, the biotic and abiotic components covering organic matter including soil life, mineral particles, soil, air and water exist in a stage of dynamic equilibrium and regulate the ecosystem processes in mutual harmony by complementing and supplementing each other. When the soil is in good health, the population of soil flora and fauna multiplies rapidly, which in turn, will sustain the biochemical process of dissolution and synthesis at a high rate. This shall enhance the regenerative capacity of soil and make it resilient to absorb the effects of climatic vicissitudes.

The principal elements to be considered are:

Maintaining a living soil

Making available the essential nutrients

Organic mulching for soil conservation

Attaining sustainable high yields

2. Why organic farming?

Heavy use of pesticides, the appearance of artificial fertilizers and less use of organic manure has weakened the ecological base in addition to degrading the organic matter content of soil in the last five decades and hence, dwindling yields. The synthetic fertilizers are neglecting the use of organic manures and biofertilizers and hence have paved the way for deterioration of soil health and in turn ill-effects on plants, human being and livestock (Choudhry, 2005). Nowadays, the practical application of organic farming offers a remedy to cure the ills of modern chemical agriculture (Kunnal, 1997). There are concerted efforts world wide to use green manuring, legumes and organic manures to provide the same amount of food with less fossil fuel based inorganic fertilizers. Increased recycling of plant residues, agro-industrial wastes, municipal wastes and animal manures is likely to complement the N availability and reduce dependence on mineral N fertilizers (Chambers et al., 2000). In addition, use of chemical fertilizers alone does not sustain productivity under continuous intensive cropping, whereas inclusion of organic materials in addition to supplying nutrients, improve the physico-chemical condition of soils, enhance nutrient cycling and build the soil organic-matter (SOM) capital (Palm, 1995; Reeves, 1997; Benbi et al., 1998; Arriaga and Lowery, 2003; Tulema et al., 2007) and increases crop yield (Arriaga and Lowery, 2003; Yaduvanshi, 2003; Nyiraneza and Snapp, 2007).

Organic materials hold great promise due to their local availability as a source of multiple nutrients and ability to improve soil characteristics. According to several authors the improvement of fertility and quality of soil, especially under low input agricultural systems, requires the input of organic materials (Stamatiadis et al., 1999; De Jager et al., 2001; Palm et al., 2001; Ouedraogo et al., 2001; Soumare et al., 2003; Nyiraneza, 2009). The effect of organic nutrients on crop yield is long term and not immediate, thus, farmers are reluctant to use organic fertilizers in their cropping system. It has been reported that the source of N in organically managed systems will restrict crop productivity, particularly of non-legumes, by limiting the amount of N released during the period of rapid crop growth (Pang and Letey, 2000; Berry et al., 2002). Therefore, combined application of two or more sources of organic manures is one of the ways to improve the nutrient supply and also to some extent synchronize the nutrient supply with crop requirement and is likely to improve the soil fertility and thereby crop performance. The use of effective microorganisms (EM) inoculums along with organic/inorganic materials is an effective technique for stimulating supply and release of nutrients from these nutrient sources. Some studies have shown that the inoculation of agro-ecosystems with EM cultures can improve soil and crop quality (Higa and Parr, 1994; Hussain et al., 1999). Similarly, Daly and Stewart (1999) reported that application of EM to onion, pea and sweet corn increased yields by 29%, 31% and 23%, respectively. Higa and Wididana (1991) stated that EM is not a substitute for other management practices but is an additive for optimizing all other amendments and practices used for crop production. Findings of various studies provided a sound base to believe that organic manures can replace the application of inorganic fertilizers for obtaining maximum yields and net benefit (Abou El- Magd, 2006; Naeem, 2006; Somasundaram, 2007; Hendawy, 2008).

3. Recent global statistics on organic farming

Organic agriculture is developing rapidly and is now practiced in more than 120 countries of the world (Fig. 2). Its share of agricultural land and farms continues to grow in many countries. Furthermore, it can reasonably be assumed that uncertified organic farming is practiced in even more countries. According to the latest survey on organic farming worldwide, almost 31 million hectares are currently managed organically by at least 633,891 farms. This constitutes 0.7 percent of the agricultural land of the countries covered by the survey.

Organic agriculture is developing rapidly, and statistical information is now available from 141 countries of the world. Its share of agricultural land and farms continues to grow in many countries. The main results of the global survey on certified organic farming show that 32.2 million hectares of agricultural land are managed organically by more than 1.2 million producers, including smallholders. In addition to the agricultural land, there are 0.4 million hectares of certified organic aquaculture.

About one third of the world's organically managed land (almost 11 million hectares) is located in developing countries. Most of this land is in Latin American countries, with Asia and Africa in second and third place respectively. Countries with the largest area under organic management are Argentina, Brazil, China, India and Uruguay.

The countries with the highest numbers of producers are Uganda, India and Ethiopia. Almost half of the world's organic producers are in Africa.

Almost 31 million hectares are organic wild collection areas and for bee keeping. The majority of this land is in developing countries - quite the opposite of agricultural land, of which two thirds is in developed countries.

Almost two thirds of the land under organic management is grassland (20 million hectares). The cropped area (arable land and permanent crops) constitutes 7.8 million hectares

On a global level, the organic land area increased by almost 1.5 million hectares compared to the data from 2006. Twenty-eight percent (or 1.4 million hectares) more land under organic management was reported for Latin America (including 0.9 million hectares of in-conversion land in Brazil for which no data had been available previously). In Europe, organically managed land increased by 0.33 million hectares (+ 4 percent) and by 0.18 million hectares (+27 percent) in Africa (IFOAM, 2009).

4. Techniques, practices and specialized forms of organic farming

Organic farming involves the use of natural organic inputs like FYM, compost, green manure, oil cakes, press mud etc (Purohit and Gehlot, 2006). Application of organic matter and their composted products for improving the soil productivity and health was reported earlier (Ramesh et al., 2006). Animal manures and crop residues are available in abundance in India (Bhattacharyya and Kumar, 2005; Ramesh et al., 2005), and their use to replenish organic matter and improve soil structure and fertility is increasingly favoured (Guisquiani et al., 1995; Parham et al., 2002; Saviozzi et al., 2002). A growing number of experiments show that organic farming leads to higher soil quality and more biological activity in soil than conventional farming (Alfoldi et al., 1993; Drinkwater et al., 1995; Droogers and Bouma, 1996). Organic farming systems have also been shown to use nutrients and energy more efficiently than conventionally managed system (Mader et al., 2002). Efficient disposal and management of organic wastes is an important issue worldwide and has become more rigorous due to rapidly increasing population, intensive agriculture, and industrialization (Garg et al., 2006). Production of large quantities of organic wastes all over the world poses major environmental (offensive odors, contamination of ground water and soil) and disposal problems (Edwards and Bater, 1992). Therefore, the disposal of different types of wastes has become very important issue to maintain the healthy environment (Senapaty and Julka, 1993). One of the best possible alternatives to manage this resource is its bioconversion to organic manure. Some of the techniques and practices integral to organic farming are detailed below.

4.1. Composting and vermicomposting

The compositing and vermicomposting technology makes possible the utilization of organic wastes, the disposal of which is a major problem now a day. Natural recycling of farm-waste organic matter through composting is a procedure aimed at minimizing losses of nutrients, reducing the accumulation of wastes and limiting greenhouse gas emission. Compost enhances the environmental sustainability of agriculture by decreasing chemical inputs and increasing soil organic matter (Mathur et al., 1993). Manure mineralized by microorganisms after incorporating into the soil provides nutrients and manure increases the water-holding capacity and cation exchange capacity of soil (Kramer and Boyer, 1995). Hence, it produces multiple effects on agronomical properties of the soil and serves as a source of macro- and micro-nutrients which improve plant growth and productivity. Vermicompost is of great value because of the presence of readily available plant nutrients, growth promoting substances, and number of beneficial microorganisms like N2 fixing, P solubilising and cellulose decomposing organisms (Sultan, 1997).

The combination of composting and vermicomposting has recently been considered as a way of achieving stabilized substrates (Tognetti et al., 2007) for improving soil fertility. Composting enables sanitization of the waste and elimination of toxic compounds, and the subsequent vermicomposting reduces particle size and increases nutrient availability; In addition, inoculation of microbial cultures along with earthworms reduces the expense and duration of the treatment process (Ndegwa and Thompson, 2001; Lazcano et al., 2008). A huge quantity of crop wastes/residues and animal wastes are always available on a farm. The common practice is to burn plant wastes, which, besides being an environmental disaster, is also a waste of the huge potential of these residues. Properly recycled, these residues form excellent compost in one to six months, depending upon the composting process used. Every farm can choose or even develop a suitable compost process depending upon its own needs and resources, including availability of labour, managerial time and investment potential. Vermicomposting is gaining worldwide popularity as a means of waste remediation and production of organic manure (vermicompost) and animal protein for poultry and fish feed. Vermicomposting involves the bio-oxidation and stabilization of organic material by the joint action of earthworms and microorganisms. Although it is the microorganisms that biochemically degrade the organic matter, earthworms are the crucial drivers of the process, as they aerate, condition and fragment the substrate, thereby drastically altering the microbial activity (Lazcano et al., 2008). Earthworms act as mechanical blenders and by comminuting the organic matter they modify its physical and chemical status by gradually reducing the ratio of C:N and increasing the surface area exposed to microorganisms - thus making it much more favourable for microbial activity and further decomposition (Domínguez et al., 1997). Vermicompost is a mixture of worm castings, organic material, humus, living earthworms, cocoons and other organisms. Vermicompost is homogenous, with desirable aesthetics, plant growth hormones and high levels of soil enzymes and tending to hold more nutrients over longer periods without adverse impacts on the environment (Ndegwa and Thompson, 2001). Considerable work has been carried out on vermicomposting of various organic materials such as animal dung, agricultural waste, forestry wastes, city waste leaf litter and food wastes (Hand et al., 1988a; Logsdon, 1994; Madan et al., 1988; Singh and Sharma, 2002). Similarly, industrial wastes such as guar gum industrial waste, paper pulp, and distillery wastes have been vermi-composted and turned into nutrient rich manure (Sundaravadivel and Ismail, 1995; Suthar, 2006; Suthar, 2007).

4.2. Biodynamics

The father of biodynamics is the Austrian anthroposophist Rudolf Steiner and it is much more than organic farming. Biodynamics is essentially a science of life forces and recognition of the role of nature and "higher forces" in agriculture. A farm is considered a living, dynamic and spiritual entity with its own rhythms and life forces. Biodynamics is a vast subject and a farm can be managed entirely on its principles and practices. It has two basic components - farming operations on the basis of an astronomical calendar, and the use of some very special preparations, which are used as sprays and in the compost heap. Biodynamics addresses soil and plant health, pest control, composting, the relationship of the soil and the plant, food quality, animal husbandry and animal welfare measures. Biodynamics is today perhaps the largest "specialised" organic farming system in the world (Gujaral, 2006).

4.3. Mulching and green manuring

The ultimate solution to organic manuring lies perhaps in the sustained promotion concept of in situ generation of organic matter in the cropped land itself by suitably modifying and modulation the cropping practices. All these techniques are different but somewhat interrelated. Mulching is the use of organic materials (plastic mulch is expensive and nonbiodegradable) to cover the soil, especially around plants to keep down evaporation and water loss, besides adding valuable nutrients to the soil as they decompose. Mulching is a regular process and does require some labour and plenty of organic material, but has excellent effects, including encouraging the growth of soil fauna such as earthworms, preventing soil erosion to some extent and weed control.

Green manuring is a low cost but effective technology in minimizing the investment cost of fertilizers and in safeguarding the productive capacity of the soil. It is a well known fact that N, for which soils have the greatest hunger, is a costly plant nutrient. This can be cheaply obtained by the inclusion of leguminous crops in rotations and their ploughing under. Legumes are usually utilized as green manure crops as they fix atmospheric N in the root nodules through symbiotic association with a bacterium, Rhizobium and leave part of it for utilization of the companion or succeeding crop. Green manuring is an age-old practice prevalent since ancient times. A crop like dhaincha (Sesbania aculeata), sunnhemp or horsebean is sown (usually) just before the monsoons. A mix is also possible. Just around flowering (30-45 days after sowing), the crop is cut down and mixed into the soil after which the season's main crop is sown. Green manuring is beneficial in two ways - firstly it fixes nitrogen, and secondly the addition of biomass (around five to ten tons/acre) greatly helps in improving the soil texture and water holding capacity. Green leaf manuring can also be carried out if sufficient leguminous tree leaves are available. Cover cropping is normally carried out also with nitrogen-fixing crops that grow fast and require little or no inputs like water or additional manuring. While cover crops can yield some returns, they are mostly used for covering the soil in the fallow months, adding nitrogen to the soil, suppressing weeds, preventing soil erosion and later used as biomass or fodder. Velvet bean is an example, and it finds use as a fodder crop and biomass generator. Another useful cover crop is Dolichos lablab, which is a source of fodder and food.

Growing of leguminous green manure crops such as sunhemp (Crotalaria juncea), dhaincha (Sesbanis aculeata), green gram (Phaseolus sp.), cowpea (Vigna unguiculata), Khesari (Lathyrus sativus), berseem (Trifolium alexandrium) and insitu mulching adds 8-28 tonnes/ha of organic manure. Green manuring of dhaincha with Azolla inoculation at 3 tonnes/ha resulted in the grain yield similar to 90 Kg N.

4.4. Crop rotation and polyculture

One of the most important aspects of organic farming is the strict avoidance of monoculture, whether annuals or perennials. Besides the proverbial "putting all eggs into one basket", monoculture systems are unhealthy for the ecosystem they are a part of. The prime requirement for any natural ecosystem to thrive and be healthy is diversity. The concept of polyculture should not be limited to plants only but extended to cover the whole farm. This way, one system's wastes and by-products are another system's inputs, or one system is comprised of more than one component, which allows for efficient use of available resources.

4.4.1. Crop rotation

Crop rotation is the sequence of cropping where two dissimilar type of crops follow each other - a few examples include cereals and legumes, deep-rooted and short rooted plants and where the second crop can make use of the manuring or irrigation provided some months earlier to the first crop (e.g. rice + wheat, rice + cotton). The combinations possible are endless, and will depend to a great deal on the local situations.

4.4.1. Multi-cropping

Multi-cropping is the simultaneous cultivation of two or more crops. In Indian agricultural tradition, farmers have been known to sow as many as 15 types of crops at one time. An example of multi-cropping is Tomatoes + Onions + Marigold (where the marigolds repel some of tomato's pests).

4.4.2. Inter-cropping

Inter-cropping is the cultivation of another crop in the spaces available between the main crop. A good example is the multi-tier system of coconut + banana + pineapple/ginger/leguminous fodder/medicinal or aromatic plants. While ensuring biodiversity within a farm, inter-cropping also allows for maximum use of resources.

4.5. Effective Microorganisms

EM, like Biodynamics can be useful in many different ways on the farm, including improving soil health, as a pest repellent and prophylactic, in composting, and in animal feeds, animal health and hygiene, aquaculture, etc. Different EM cultures are used for agriculture, animal husbandry, and aquaculture.

4.5. Integration of systems

In nature, the whole is greater than the sum of its parts and the key to the success of any natural system is diversity. Diversity adds complexity to the farm system lending it greater stability. There are economic and productivity benefits too.

5. Organic farming and genetic engineering

Organic farming and genetic engineering are two contradictory world views, two different philosophies, the two main options for the future. The basic principles of organic farming are holistic. Rather than looking at isolated parts, the whole farm as a living entity is the focus. It is seen as a whole, enmeshed in the intrinsic web of life and part of the interactions and relationships between all living beings. Organic farming seeks to maintain an overall balance, by enhancing biodiversity (for example, flowering plants are sown on the borders of fields to attract beneficial insects into the crops). Organic pesticides are only used in emergencies cases, as supplementary measures or technical solution. The very basis of genetic engineering depends on the search for single factor-solutions, whereas all major problems of the environment and agriculture are ultifactoral.

For example, Bt-maize expresses a toxin that kills the maize pest stemborer. But what if other, often beneficial, insects (such as lacewings, the monarch- or the black swallowtail-butterfly) are harmed as well? What consequences follow if the toxin also influences the soil-food-web or if the stemborer acquires a resistance to the Bt toxin?

6. Nutrient management in organic farming

Organic farming is often understood as a form of agriculture with use of only organic inputs for the supply of nutrients and management of pests and diseases. In fact, it is a specialized form of diversified agriculture, wherein problems of farming are managed using local resources alone. True, organic resources availability is limited; but under conditions of soil constraints and climate beggaries, organic inputs use has proved more profitable compared to agrochemicals (Huang et al, 1993). Organic farming systems rely on the management of soil organic matter to enhance the chemical, biological and physical properties of the soil. One of the basic principles of soil fertility management in organic systems is that plant nutrition depends on 'biologically-derived nutrients' instead of using readily soluble forms of nutrients; less available forms of nutrients such as those in bulky organic materials are used. This requires release of nutrients to the plant via the activity of soil microbes and soil animals. Improved soil biological activity is also known to play a key role in suppressing weeds, pests and diseases (IFOAM, 1998). Animal dung, crop residues, green manure, biofertilizers and bio-solids from agro-industries and food processing wastes are some of the potential sources of nutrients of organic farming. While animal dung has competitive uses as fuel, it is extensively used in the form of farmyard manure. India produces about 1800 mt of animal dung per annum. Even if two-thirds of the dung is used for biogas generation, it is expected to yield biogas not less than 120 mm3 per day. In addition, the manure produced would be about 440 mt per year (Ramaswamy, 1999), which is equivalent to 2.90 mt N, 2.75 mt P2O5 and 1.89 mt K2O.

7. Organic food: nutritional quality

Organic food is derived from crops or animals produced in a farming system that avoids the use of man-made fertilizers, pesticides, growth regulators and livestock feed additives. Organic farming systems rely on crop rotation, animal and plant manures, some hand weeding and biological pest control. The view that organic foods are 'healthier' than conventionally-produced foods appears to be based on the perception that organic foods have superior sensory attributes, contain lower levels of pesticides and synthetic fertilizers and have higher levels of nutrients and protective phytochemicals. Conversely, it has also been suggested that application of manure and reduced use of fungicides and antibiotics in organic farming could result in a greater contamination of organic foods by microorganisms or microbial products.

There have been very few scientific studies in which foods grown conventionally have been compared, under comparable and controlled conditions, with those produced organically, in terms of their nutrient composition or their biological effects on animals or human subjects. I would appear that few differences can be demonstrated, and where differences are detected they are very small (Williams, 2002).

8. Advantages of organic farming8.1. Enrichment of soil with organic matter: Plant nutrient management

All these techniques are different but somewhat interrelated. Mulching is the use of organic materials (plastic mulch is expensive and non-biodegradable) to cover the soil, especially around plants to keep down evaporation and water loss, besides adding valuable nutrients to the soil as they decompose. Mulching is a regular process and does require some labour and plenty of organic material, but has excellent effects, including encouraging the growth of soil fauna such as earthworms preventing soil erosion to some extent and weed control. Green manuring is an age old practice prevalent since ancient times. A crop like Dhaincha (Sesbania aculeata), sunnhemp or horsebean is sown (usually) just before the monsoons. A mix is also possible. Just around flowering (30-45 days after sowing), the crop is cut down and mixed into the soil after which the season's main crop is sown. Green manuring is beneficial in two ways - firstly it fixes nitrogen, and secondly the addition of biomass (around five to ten tons/acre) greatly helps in improving the soil texture and water holding capacity. Green leaf manuring can also be carried out if sufficient leguminous tree leaves are available. Cover cropping is normally carried out also with nitrogen fixing crops that grow fast and require little or no inputs like water or additional manuring. While cover crops can yield some returns, they are mostly used for covering the soil in the fallow months, adding nitrogen to the soil, suppressing weeds, preventing soil erosion and later used as biomass or fodder. Velvet bean is an example, and it finds use as a fodder crop and biomass generator. Another useful cover crop is Dolichos lablab, which is a source of fodder and food (Gujaral., 2006).

8.2. Pest and disease management in organic farming

Pest control in organic farming begins by making sensible choices, such as growing crops that are naturally resistant to diseases and pests, or choosing sowing times that prevent pest and disease outbreaks. Careful management in both time and space of planting not only prevents pests, but also increases population of natural predators that can contribute to the control of insects, diseases and weeds (FAO, 2003). Organic farmers have long maintained that synthetic fertilizers and pesticides increase crop susceptibility to pests (Yepson, 1976). Organic crops have been shown to be more tolerant as well as resistant to insect attack (Lotter, 1999). Organic rice is reported to have thicker cell walls and lower levels of free amino acid than conventional rice (Kajimura et al., 1995). Free amino acids, associated with high N applications, have been reported to increase pest attack (Hedin et al., 1993). Soil-borne root diseases are generally less severe on organic farms than conventional farms, while there were no consistent differences in foliar diseases between the systems. The successful control of root diseases in organic systems is likely to be related to the use of long and diverse crop rotations, crop mixtures and regular application of organic amendments (Vanbruggen, 1995).

8.3. Key advantages of Organic farming:

Organic manures produce optimal conditions in the soil for high yields and good quality crops therefore reduce the needs of purchased inputs.

They supply all nutrients required by the plant (NP K, secondary and micronutrients).

They improve plant growth and physiological activities of the plants.

They improve the soil physical properties such as granulation and good tilth, giving better aeration, easy root penetration and improved water holding capacity. The fibrous portion of the organic matter with its high carbon content promotes soil aggregation to improve the permeability and aeration of clayey soils while its ability to absorb moisture helps in the granulation of sandy soils and improves their water holding capacity. The carbon in the organic matter is the source of energy for microbes which help in aggregation.

They improve soil chemical properties such as supply and retention of soil nutrients and promote favorable chemical reactions.

Most of the organic manures are wastes or byproducts which on accumulation may lead to pollution. Thus utilizing them for organic farming, pollution is minimized.

Organic manures are considered as complete plant food. Organic matter restores the pH of the soil which may become acid due to continuous application of chemical fertilizers.

Organically grown crops are believed to provide healthier and nutritiously superior food for man and animals than those grown with commercial fertilizers.

Organically grown plants are more resistant to pests and diseases and hence only a few other protective treatments are required.

Organic farming helps to prevent environmental degradation and can be used to regenerate degraded areas.

Since the basic aim is diversification of crops, much more secure income can be obtained than to rely on only one crop enterprise.

There is an increasing consumer demand for agricultural produce which are free of toxic chemical residues.

8.4. Benefits of organic farming

The benefits of organic farming can be classified under three broad headings: (i) the enterprise mix (mixed livestock and cropping instead of specialization; crop rotation instead of monoculture etc), (ii) the treatment of the cropped area (avoidance of agro chemicals; less intensive approach etc) and (iii) the boundary features (field margins, more and larger hedges etc.). But, what is the origin of these? Organic farming is a particular whole farm "systems" approach. It is often discussed as a collection of different practices, but it is actually the whole package of the approach and all the individual practices.

Organic farming is based on a set of principles, such as: a holistic approach to farming (instead of addressing problems individually); the creation and maintenance of conditions that positively nurture the health of the crops/livestock (instead of solely treating the symptoms of problems, e.g., by applying chemicals); and, the harnessing of natural processes (instead of using artificial inputs). Thus, for example, agro-chemicals are avoided and instead alternative practices based on these principles are used. Many involve the positive use of biodiversity (through the soil, field margins, hedges etc.), thus making the conservation of biodiversity an integral part of the farming activity. For example, the soil is treated as a living entity, not simply as a substrate for crops to grow in. The standards for organic farming were developed long after organic farming had been established, but are now used as a template and guide for the practice of organic farming. They are legally regulated and their implementation policed by the organic certifying bodies. Some standards are obligatory, others are "recommended". With the latter, many are actually the most practical organic approach and so are also the standard practices. In addition, there are special 'conservation' standards to ensure that specific conservation issues are addressed in more detail. Some of the biodiversity benefits of organic farming can be directly linked to particular standards (e.g., avoiding the use of agro-chemicals, the use of grass leys), others are an indirect result of the standards (e.g., mixed crop/livestock farming, mixed spring/autumn sowing), and yet others are the result of the farmers applying the principles and approach of organic farming in a way tailored to their situation and for issues and to a detail not dealt with by the standards. It is sometimes asked if conventional farming can recreate the advantages of organic farming by adopting its practices. However, as many of the benefits result from the whole system not just the individual practices, and as very fundamental changes are needed to deliver many aspects of organic farming, this is not realistic and many of the benefits will not be achievable. For example, no other system prohibits the use of herbicides and synthetic pesticides in crop production, thus the benefits of this cannot be achieved. Similarly, no other system so completely relies on alternative practices, so these will not be developed to the same degree and some not used at all. Conventional farming methods do not have comprehensive standards, legislation, and regular inspection procedures, thus the benefits of control and accountability would not be delivered. Finally, the individual can always deliver important additional benefits (probably comparatively more important in conventional agriculture) but, 27 other systems do not use the principles of organic farming, thus the commitment and environmentally sensitive approach of the individual farmer is not developed to the same degree by the system. In conclusion, the total range, degree and quality of the benefits of organic farming is delivered by the whole package of the approach, not simply by the individual practices required by the standards. The adoption of certain organic farming practices by conventional systems will improve conventional farming, but it will not deliver the biodiversity benefits of organic farming (The Soil Association., 2000).

8.5. Organic farming and sustainability

The main question confronting organic and sustainable farming is: how can farmers increase their yields with cheap, locally available and simple technologies, without damaging the environment? Today, concerns about sustainability centre on the need to develop agricultural technologies and practices that: (i) do not have adverse effects on the environment (partly because the environment is an important asset for farming), (ii) are accessible to and effective for farmers, and (iii) lead to both improvements in food productivity and have positive side effects on environmental goods and services. Sustainability in agricultural systems incorporates concepts of both resilience (the capacity of systems to buffer shocks and stresses) and persistence (the capacity of systems to continue over long periods), and addresses many wider economic, social and environmental outcomes. Organic management restores, maintains, and enhances ecological harmony rather than creating a steady dependency on artificial pesticides and fertilizers. So successful is this technology that the organic food industry is the fastest growing sector of the commercial food system, increasing by more than 20% a year (Sligh, 2002). What distinguishes organic agriculture from industrial farming? Organic agriculture promotes and enhances biodiversity rather than creating catastrophic environmental and health impacts. The biological life cycles of plants, animals, and soil provide the basis for the nutritional needs of the farm, rather than artificial fertilizers. Organic management restores, maintains, and enhances ecological harmony rather than creating a steady dependency on artificial pesticides and fertilizers. The essential values of organic agriculture (i.e., organic integrity) encompass three key elements: environmental stewardship, accountability, and a fair pricing system, according to Michael Sligh, the director of Sustainable Agriculture at the Rural Advancement Foundation International- USA (Sligh, 2002). As concerns about climate change and energy scarcity increase, we need to reduce both the energy inputs and greenhouse gas outputs of our current food production system. Organic farming shows proven benefits on each of these counts, but many critics have argued that a large-scale organic conversion would entail dramatic reductions in global food yields, leading to widespread famine. This has led to a surge of interest in the question, 'Can organic farming feed the world?' Over the same period, world population has grown from three billion to more than six billion, imposing an increasing impact of the human footprint on the Earth as consumption patterns change (Kitzes et al., 2008; Pretty, 2007). At the same time as these recent changes in agricultural productivity, consumer behaviour over food (Smith, 2008) and the political economy of farming and food (Goodman and Watts, 1997), agricultural systems are now recognized to be a significant source of environmental harm (Tilman, 1999; Pretty et al., 2000; MEA, 2005). During this period, the intensity of production on agricultural lands has also risen substantially (Hazell and Wood, 2008). The use of pesticides in agriculture has also increased dramatically and now amounts to some 2.56 billion kg yrK1. In the early twenty-first century, the annual value of the global market was US$25 billion, of which some US$3 billion of sales was in developing countries (Pretty, 2005). Herbicides account for 49% of use, insecticides 25%, fungicides 22% and others approximately 3% (table 1). The inefficient use of some of these inputs has, however, led to considerable environmental harm. Increased agricultural area contributes substantially to the loss of habitats, associated biodiversity and their valuable environmental services (MEA, 2005; Scherr and McNeely, 2008). Approximately 30-80% of nitrogen applied to farmland escapes to contaminate water systems and the atmosphere as well as increasing the incidence of some disease vectors (Smil 2001; Victor and Reuben, 2002; Pretty et al., 2003; Townsend et al., 2003; Giles, 2005; Goulding et al., 2008). Irrigation water is often used inefficiently and causes water logging and salinization, as well as diverts water from other domestic and industrial users; and agricultural machinery has increased the consumption of fossil fuels in food production (Leach, 1976; Stout, 1998).

8.6. Organic farming and soil health

Organic farming is a matter of giving back to the nature what was taken back from it. It is a system of farming based on integral relationship between soil, plant, water and microflora. Organic farming, therefore, is a farming system devoid of chemical inputs, in which the biological potential of the soil and underground water resources are conserved and protected from the natural and human induced degradation or depletion by adopting suitable cropping models and methods of organic replenishment, besides natural and biological means which are used for pests and disease management. The principal concept is that organic farming is the farming based on natural principles which alone are sustainable. Organic farming, therefore, envisages a comprehensive management to improve the health of the soil. When the soil is in good health, the soil flora and fauna grow rapidly, become activated and facilitate the biochemical processes at a faster rate.

Organic farming techniques will help to increase the organic matter content of the soil, thus reducing the bulk density and decreasing compaction. There can be effective conservation systems since they provide soil cover during most of the year (little run-off and erosion) and with the greater use of rotation and green manure crops, crop residues and legumes, there is an increased emphasis on manure as a source of soil fertility. Tropical soils are generally low in organic content. The low organic matter is primarily due to climate particularly due on high temperature and secondarily due to cultural practices. Organic matter increases with rainfall. In tropical and sub-tropical regions, although much organic matter is produced, it decays very rapidly. Whatever organic matter is added to the soil will be decomposed very fast (over 90 % in a year) and hence it is a Herculean task to raise the organic matter content of the soil.

8.7. Organic agriculture and food security

The common claims that large-scale conversion to organic agriculture would result in drastic reduction in world food supplies or large increases in conversion of undisturbed lands to agriculture (Avery, 1995; Trewavas, 2001). Widespread conversion to organic agriculture would result in crop yield increase over the current averages as a result of increased investment in research and extension (Lampkin, 1994). Organic farmers grow a variety of crops and maintain livestock in order to optimize use of nutrients and the space between species. This ensures economic advantages through low crop production or yield failure due to biotic and abiotic factors in all of these simultaneously. This can have an important impact on local food security and resilience. In rain-fed systems, organic agriculture has demonstrated to out-perform conventional agricultural systems under environmental stress conditions (Stanhill, 1990; Wynen, 1994; Peters, 1994). At the global level, especially in developing countries with high population pressure, and with the present state of knowledge and technology, organic farmers cannot produce enough food for everybody.

9. Conclusion

The interest in organic agriculture is growing globally, because it requires less financial input and places more reliance on the natural and human resources available. Studies to date seem to indicate that organic agriculture offers comparative advantage in areas with less rainfall and relatively low natural and soil fertility levels. Organic agriculture does not need costly investments in irrigation, energy and external inputs, but rather organic agricultural policies have the potential to improve local food security, especially in marginal areas. Possibly, the greatest impact of organic agriculture is on the mindset of people. It uses traditional and indigenous farming knowledge, while introducing selected modern technologies to manage and enhance diversity, to incorporate biological principles and resources into farming systems, and to ecologically intensify agricultural production. Thus through greater emphasis on use of local resources and self-reliance, conversion to organic agriculture definitely contributes to the empowerment of farmers and local communities.

Acknowledgements