The word "sustain," from the Latin sustinere (sus-, from below and tenere, to hold), to keep in existence or maintain, implies long-term support or permanence. As it pertains to agriculture, sustainable describes farming systems that are "capable of maintaining their productivity and usefulness to society indefinitely. Such systems must be resource-conserving, socially supportive, commercially competitive, and environmentally sound."
"A systems approach is essential to understanding sustainability. The system is envisioned in its broadest sense, from the individual farm, to the local ecosystem, and to communities affected by this farming system both locally and globally… A systems approach gives us the tools to explore the interconnections between farming and other aspects of our environment." "Environmental sustainability implies the following:
• meeting the basic needs of all peoples, and giving this priority over meeting the greeds of a few
• keeping population densities, if possible, below the carrying capacity of the region
• adjusting consumption patterns and the design and management of systems to permit the renewal of renewable resources
• conserving, recycling, and establishing priorities for the use of nonrenewable resources
• keeping environmental impact below the level required to allow the systems affected to recover and continue to evolve.
"An environmentally sustainable agriculture is one that is compatible with and supportive of the above criteria”.
Various definitions have been provided for what constitutes sustainable agriculture, ranging from the narrow focus on economics or production to the incorporation of culture and ecology. Wendell Berry has simply said, “A sustainable agriculture does not deplete soils or people."
Sustainable agriculture is a form of agriculture aimed at meeting the needs of the present generation without endangering the resource base of the future generations. In order to feed the burgeoning population more food has to be produced and this has to be done without degradation of the resource base.
Over time, the International Alliance for Sustainable Agriculture and an increasing number of researchers, farmers, policy-makers and organizations worldwide have developed a definition that unifies many diverse elements into a widely adopted, comprehensive, working definition: A sustainable agriculture is ecologically sound, economically viable, socially just and humane. These four goals for sustainability can be applied to all aspects of any agricultural system, from production and marketing to processing and consumption. Rather than dictating what methods can and can not be used, they establish basic standards by which widely divergent agricultural practices and conditions can be evaluated and modified, if necessary to create sustainable systems. The result is an agriculture designed to last and be passed on to future generations. Conceived in this sense, sustainable agriculture presents a positive response to the limits and problems of both traditional and modern agriculture. It is neither a return to the past nor an idolatry of the new. Rather, it seeks to take the best aspects of both traditional wisdom and the latest scientific advances. This results in integrated, nature-based agro-ecosystems designed to be selfreliant, resource-conserving and productive in both the short and long terms.
The increasing substitution of the term "agribusiness" for "agriculture" reflects a fundamental shift to a monetized economy in which everything, including human beings, is assigned a certain value. Such a system leads to an increased sense of competition, isolation and alienation. As rural societies break down, their values are lost as the backbone of the larger society. Without such a backbone, agriculture is neither humane nor sustainable.
Basic Features and Concepts of Sustainable Systems
Agriculture Types and Objectives
| Type of Agriculture | Objective | Input | Output |
|---|---|---|---|
| Subsistence Agriculture (low level equilibrium) | To sustain life and family needs | Low | Low |
| Commercial Farming (high level equilibrium) | To obtain high income | High | High |
| Sustainable Agriculture (Natural or Ecological equilibrium) | Ecological balance | Low | High |
Watershed Management
The important developmental activities in watershed management for drylands are soil and moisture conservation measures, land use based on land capability, wasteland management, afforestation and efficient crop production practices.
Conservation of Genetic Resources
Tillage
Nutrient Management
Nutrients needed for the crop are met from organic sources. For example, when rice is gown by selfreliant organic farming system, green manure crops-sunhemp, dhaincha and pillipesara are sown as a mixture in a 1: 1: 1 ratio and 25 kg seed of each are sown in a hectare. The green manure crop is incorporated after 40 days and two weeks are allowed for decomposition before planting rice. Instead of top dressing of chemical fertilizers like urea; ammonium sulphate, calcium ammonium nitrate etc., biogas slurry and fresh cattle urine diluted with irrigation water are pumped to the fields. Three such irrigations are given at monthly intervals. If the crop is weak, one more irrigation is given with slurry combination. Farm-grown inputs like Azolla, blue green algae, Azotobacter, Rhizobium and other biofertilizers are used judiciously. Crop rotation with legumes is adopted for building soil fertility. Sustainable agriculture mainly depends on soil organic matter for nutrient supply through farmyard manure, compost and green manures. In the initial stage of conversion, supplemental fertilizer application is necessary until equilibrium of nutrient cycles is established.
Efficient Water Management
Water management can be subdivided into rain water management and irrigation water management. The important aspects of rain water management are water harvesting, supplemental irrigation and reduction of evapotranspiration. Irrigation water management involves scheduling irrigation at appropriate time with adequate quantity of water without causing waterlogging, salinity and alkalinity. .
Weed Management
Weed control methods include cultural, physical, biological and chemical methods. In sustainable agriculture, cultural, physical and biological methods are given greater importance. Weeds are generally controlled by rotation, tillage and hand-weeding. Weed population to an extent can be tolerated at certain periods of crop growth as they help in nutrient recycling, pest control, soil conservation and organic matter improvement.
Pest Management
Occurrence of insects and diseases are less in organic farming probably due to greater plant and insect diversity within the redesigned agro-ecosystem. The incidence of livestock diseases is much lower than in conventional farming. The probable reasons include higher feed quality. In natural biological communities, certain equilibrium between plants and animal organisms is involved. Rare, widely dispersed and abundant species exist. Natural regulation in the form of an increase in disease and enemies and also shortage of food cause decline in population. In the absence of plant protection measures, it is estimated that on an average 20 to 30 per cent of yield loss occurs. Maximal yield requires the highest degree of protection and is correspondingly more expensive. Excessive use of chemicals not only results in waste of money and energy but also builds up resistance and resurgence in insects and pathogens. Pathogens developing resistance to the chemicals is increasingly observed with the introduction of systemic chemicals.
Integrated pest control which combines cultural and biological methods and use of resistant varieties reduce dependence on ecologically aggressive chemical pesticides. Plant derived compounds such as neem and microbial control agents such as bacteria and fungi can be used instead of harmful chemicals. Helpful insects and spiders are encouraged. If it becomes necessary to control insects by insecticides, thresh hold levels of insect population have to be considered before making a decision to spray. For example, brown plant hopper on rice has to be controlled only when its population is more than 20 per hill. It is now considered that chemical pesticides which have selective action and are compatible with biological control agents are important for sustainable agriculture. They will be of immense use in integrated pest management strategies. It is also considered that in the near foreseeable future, these chemicals cannot be replaced by any other single method of pest control.
Crop Rotation
The selection of optimal crop rotation is important for successful sustainable agriculture. Crop rotation is very important for soil fertility management, weed, insect and disease control. Legumes are essential in any rotation and should comprise 30 to 50 per cent of the crop land. A mixed cropping, pasture and livestock system is desirable or even essential for the success of sustainable agriculture.
Indices of sustainability
Quantification of sustainability is essential to assess the impact of management systems on actual and potential productivity and on environment. Some indices of sustainability include the following:
1. Productivity (Pi), Production per unit of resource used can be assessed by, Pi = P/R where, Pi is productivity, P is total production and R is resource used.
2. Total Factor Productivity (TFP), It is defined as productivity per unit cost of all factors involved (Herdt, 1993).
TFP=∑i=1n(Ri×ci)P
Where, P is total production, R is resource used and c is the cost of the resource, and n is the number of resources used in achieving total production.
3. Coefficient of sustainability (Cs), It is measure of change in soil properties in relation to production under specific management system (Lal 1991).
G=W(oi,ad,Om,t)
Where, Cs is coefficient of sustainability, oi is output per unit that maximizes per capita productivity or profit, ad is output per unit decline in the most limiting or non-renewable resource, Om is the minimum assured output, and t is the time. The time scale is important and must be carefully selected.
4. Index of sustainability (Is), It is a measure of sustainability relating productivity to change in soil and environmental characteristics (Lal, 1993; Lal and Miller 1993).
Where:
- is the Index of Sustainability.
- represents the alteration in soil properties.
- represents the change in water resources and quality.
- represents the modification in climate factors.
- is the time.
Where Is index of sustainability, Si is alteration in soil properties, Wi is change in water resources and quality, Ci is modification in climate factor and t is time.
5. Agriculture Sustainability (As). It is a broad based index based on several parameters associated with agricultural production (Lal 1993).
As=Pt+Sp+Wt+Ct+t
Where, As is agricultural sustainability, Pt is productivity per unit input of the limited or non-renewable resource, Sp is critical soil property of rooting depth, soil organic matter content, Wt is available water capacity including water quality and Ct is climatic factor such as gaseous flux from agricultural activity, and t is time.
6. Sustainable Coefficient (Sc). It is a complex and a multipurpose index on a range of parameter and is similar to As. It is defined as:
Sc= F(Pt*Pd*Pm)t
Sc= (Pi*Wt*Ct)dt
Where, Pt is productivity per unit input of the limited resource, Pd is productivity per unit decline in soil property, Sc is critical level of soil property, Wt is soil water regime and quality, Ct is climatic factor, and t is time.
Crop productivity as an indicator of sustainability
A measure of crop productivity is a good integrator of all soil, water, climatic and biotic factors. It is important to assess potential vis-à-vis actual productivity. It is science based management system, actual production exceeds potential production in soils of low inherent fertility and in harsh environments. The potential productivity, soils’ productive potential within a biome, can be estimated by several models e.g. CERES (Richie et al, 1989) and Tropical Soil Productivity calculator (Aune and Lal 1994). If land availability is a limiting factor, appropriate indices of productivity are Land use factor (L), Land use ratio (LER), and Area Time Equivalent Ratio (ATER) etc.
The Land use factor (L) is defined as the ratio of cropping period C plus fallow period F to cropping period C (Okigbo 1978).
L=C+C F
The factor L is generally high for low intensity system eg. shifting cultivation.
The LER is calculated as follow (Willey and Osiru, 1972):
LER=∑i=1n(YmYi)
Where, Yi and Ym are yields of component crops in intercrop and monoculture system, respectively and n is the number of crops involved. Because crops involved vary widely in their maturity period, ATER index considers the crop duration (Hiebsch and Mc Collum 1987).
Where, d is the growth period of the crop in days and t is the time in days for which the field remained occupied ie. the growth period of the longest duration crop. Numerical values of ATER approaches that of LER for a mixture consisting of crops of approximately identical growth periods ie.; when t = d in comparison, productivity can also be expressed in terms of the resources use efficiency of the most limiting resource e.g., water, nutrients, energy or labour.
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