Nutrient management in organic crop products
- Part 1 -

DJ Rajkhowa *

India has achieved significant progress in agri- cultural production during the last five decades due to green revolution. The food grain production increased from 51 tonnes in 1950-51 to 108 million tonnes during 1970-71, 211 million tonnes during 2000-01 and a record food grain production of 230 million tonnes during 2006-07. However, the intensive modern agriculture for the past five decades has led to several environmental and health issues.

Decline and deterioration of natural resources emerged as a serious concern for the sustainability of agricultural production. The yield stagnation, decline in soil fertility and deficiency of secondary and micro-nutrients, lowering of water table, loss of bio-diversity, loss of soil organic carbon (SOC), increase in pests and disease problems, food and feed contamination due to indiscriminate use of pesticides, development of pests resistance and decline in factor productivity are some of the negative effects of green revolution technologies.

The decline in soil productivity in terms of nutritional disorders, micro- nutrient deficiencies, poor soil physical condition, salinity, alkalinity, poor soil biological activity and the out break of pests and diseases are posing serious threat to our food security and livelihood supporting systems. In view of this organic farming is emerging as an alternative to the chemical oriented intensive agriculture.

Organic Farming -the concept

Various definitions of organic farming have been put forwarded by USDA, FAO, IFOAM etc. As per the definition given by USDA 1980-Organic farming is a production system which avoids or largely excludes the use of synthetic fertilizers, pesticides, growth regulators and livestock feed additives. Organic farming systems rely on crop rotations crop residues, animal manures, legumes, green manures, off-farm organic wastes and aspects of biological pest control to maintain soil productivity and tilth, to supply plant nutrients and to control insects, weeds and other pests.

For practical purpose the simplest definition can be "Optimum use of local resources for getting sustainable agriculture production without harming bio-physical and social environment as well as regenerative capacity of resources" (Faroda et al., 2008).

This implies non-use of external inputs that may harm environment like fertilizers, pesticides etc. Organic farming is a holistic production system that has the advantage of efficient use and recycling of locally available resources. Organic agriculture does not imply the simple replacement of synthetic fertilizers and other chemicals with organic inputs and biologi- cally active formulations.

Instead, it envisages a comprehensive management approach to improve the productivity of 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 dynamic equilibrium and regulate the ecosystem processes in mutual harmony by complementing and supplementing each other.

Organic farming relies on crop rotations, crop residues, animal manures, legumes, green manures, off farm organic wastes and aspects of biological and cultural pest control to maintain soil productivity and tilth, to supply plant nutrients and to control insects, weeds and other pets. With increasing health consciousness and concern for environment, organic farming system as been drawing attention al over the world. Demand for organic products, especially in developed countries has been increasing by leaps and bounds.

Principles of organic farming

The main principles of organic farming are: to produce high quality food in sufficient quantity, to interact in a constructive and life enhancing way with natural systems and cycles, to consider the social and ecological impact of the organic production and processing systems, to enhance biological cycles within the farming system, flora and fauna, plants and animals, to maintain and increase long term soil fertility, to protect and healthy use of water resources, to use as far as possible renewable resources in locally organized production systems, to minimize all forms of pollution, processing, and distribution chain which is both socially justifiable and ecologically responsible.

The organic community has adopted four basic principles (FAO, 2001) and broadly any systems using the methods of organic agriculture and being based on these principles may be classified organic agriculture:

(i) Principle of health: Organic agriculture should sustain and improve the health of the soil, plant, animal, human and planet as one and indivisible;
(ii) Principle of ecology-organic agriculture should be based on living ecological systems and cycles, work with them, emulate them and help sustain them;
(iii) Principle of fairness: Organic agriculture should build on relationships that ensures fairness with regard to the common environment and life opportunities and
(iv) Principle of care : Organic agriculture should be managed in a precautionary and responsible manner to protect the health and well being of current and future generations and the environment.

Characteristics of organic farming

Organic agriculture is a production system that sustains the health of soil, ecosystems and people. It relies on ecological processes, biodiversity and cycles adapted to local conditions, rather than the use of inputs with adverse effects. It combines tradition, innovation and science to benefit the shared environment and promote fair relationships and good quality of life for all involved.

Organic farming is characterized by maximum but sustainable use of local resources and minimum use of purchased inputs. It facilitates the basic biological functions of soil-water-nutrient-human continuum. In organic farming the ecological balance is maintained as well as the biodiversity is being sustained.

Improvement in soil health, low water consumption, ow input cost, high demand and market price for organic commodities due to social awareness, high export potential and sustainability of agriculture are the benefits reaped by adopting the organic farming. It can be summarized as
o Sustainable use of local resources
o Minimal use of purchased inputs
o Ensuring basic biological functions of soil-water- nutrients
o Maintenance of plant and animal diversity

When the soil is in good health, the population of soil fauna and flora multiplies rapidly which, in turn, still sustains the biochemical processes of dissolution and synthesis at a high rate. (Palaniappan, 2004). The principal elements to be considered while practicing organic farming are: o Maintaining a living soil
o Making available all the essential nutrients
o Organic mulching for conservation, and
o Attaining sustainable high yields.

Organic farming- the present scenario

At present the organic farming is practiced in more than 120 countries of the world. Globally 30.4 million hectares, which constitutes 0.65% of agricultural land are currently managed organically. Australia ranks first in terms of area under organic agriculture (12 ma ha) followed by Europe (7 ma ha), Latin America (5.8 mha), Asia (almost 2.9 m ha), North America (2.2 m ha) and Africa (0.9 m ha). The demand for organically produced commodity is increasing day by day across the globe. Global sale of organic food and drink have increased by 43% from 23 billion dollars in 2003 to 33 billion US Dollars in 2005.

India ranks 33rd in total land under organic cultivation and 88th position for agricultural land under organic crops to total farming area. Thus, the percentage share of organic land to total agricultural land is 0.3%.

Madhya Pradesh has 1.63 lakh ha of area under organic cultivation followed by Maharashtra (1.15) lakh ha, Orissa (74,585 ha), Jammu and Kashmir (32,541 ha), Rajasthan (24,868 ha) and Kerala (14,744 ha). Cotton is the single largest commodity produced under organic certification (1,42714 t) followed by pulses (45, 518 t) and rice (44,132 t).

Nutrient management in organic farming

Organic farming relies on management of soil organic matter (SOM) to enhance physical, chemical and biological soil properties. The basic idea behind organic farming is to feed the soil to maintain its health rather than to fed the crop. The basic principle of soil fertility management in organic system is that plant nutrition depends on "biologically derived nutrients" instead of using readily soluble form of nutrients. This requires release of nutrients to the plant via the activity of soil microbes and soil animals.

The basic requirement is to increase input use efficiency at each step of farm operations. This is to be achieved through reducing losses and by enrichment of nutrient contents in manures. What is now required is to harmonize and bind the components in a system synergy and all round complementary. The key to building healthy soil is organic matter management.

Building up and maintaining soil organic matter contributes to nutrient management through better soil tilth and thus root exploration, enhanced biological activity which increases mineralization and nutrient availability, and greater cation exchange capacity which enhances nutrient retention.

Soil organic matter also promotes an abundance of microorganisms that can stimulate root growth and help solubilize nutrients. Managing soil nutrients should not be separated from management of the physical and biological conditions of soil. A good nutrient management programme supports and improves all three aspects of soil health, since they are inter-related.

Besides maintaining soil health, the goal of a nutrient management programme should be to meet a crop's nutrient needs as economically as possible while avoiding application of excess nutrients. Periodic soil testing is the only way to understand the current fertility level ad maintain the fertility status of each field. Plant tissue analysis can used to verify soil fertility status, particularly for nutrients not easily measured in routine soil tests.

Critical aspect of soil fertility management include pH, major nutrients (N, P, K) secondary nutrients (S, Ca, Mg) and micronutrients (especially boron, copper, manganese, zinc, iron, molybdenum, chloride, cobalt). Soil pH is important because it influences nutrient solubility, microbial activity and root growth.

Strategies to enhance soil organic carbon (SOC)

1. Controlling soil erosion
2. Conservation tillage
3. Legume in cropping systems
4. Green and green leaf manuring
5. Carbon sequestration through agro-forestry and recycling leaf litter
6. Recycling and enhancing quality of organic wastes by effective composting methods
7. Microbes and bio-fertilizers

Availability of organic resources

The success of organic farming depends upon development and integration of various activities of farm in a way that availability of organic resources for recycling is not a constraint. The animal dung crop residues, green manure, bio-fertilizers, agro-industrial waste, food processing waste and urban and rural solid waste are some potential organic sources of nutrients.

Proper recycling of biowaste for manure production and energy generation is an important aspects of nutrient management in organic farming. India produces about 600-700 mt f agricultural wastes and 1800 mt of animal dung per year. Even if 2/3 rd of dung is used for biogas generation, it is expected to yield biogas of not less than 120 m m3 per day.

In addition, the manure produced would be about 440 mt/year which is equivalent to 2.90 mt N, 2.75 mt P2O5 and 1.89 mt of K2O. Organic systems adopt nutrient management options with primary aim to develop whole farm like a living organism with balanced growth in both crops and livestock holding. Thus, nutrient cycle is closed as far as possible. Organic agriculture is therefore often termed as knowledge based rather than input-based agriculture.

To be continued ....