Agriculture in Pakistan

Agriculture and Environment

                   Agriculture and Environment
  Introduction: This assignment consists of agriculture and its effect on the environment as well as environmental change and its impact on the agriculture.

Agriculture, or farming, is the simplification of nature's food webs and the re-channeling of energy for human planting and animal consumption.
 Another way agriculture refers to the production of food and goods through farming and forestry. Agriculture was the key development that led to the rise of civilization, with the husbandry of domesticated animals and plants (i.e. crops) creating food surpluses that enabled the development of more densely populated and stratified societies. The study of agriculture is known as agricultural science (the related practice of gardening is studied in horticulture).
Agriculture encompasses a wide variety of specialties and techniques, including ways to expand the lands suitable for plant rising, by digging water-channels and other forms of irrigation. Cultivation of crops on arable land and the pastoral herding of livestock on rangeland remain at the foundation of agriculture. In the past century there has been increasing concern to identify and quantify various forms of agriculture. In the developed world the range usually extends between sustainable agriculture (e.g. perm culture or organic agriculture) and intensive farming (e.g. industrial agriculture).
 Agriculture is necessary because-
·        Agriculture is the predominant occupation of two-third of working population for their livelihood.
·        Agriculture is the major source of income for about three-fourths of populations who live in villages.
·        Agriculture provides not only food but also raw materials for manufacturing industries like textiles, sugar, vegetable oil, jute and tobacco.
·        Agriculture is not only an important occupation of the people, but also way of life, culture and custom. Most of the Indian customs and festivals are observed in consonance with agriculture seasons, activities and products.
·       It helps in food chain.
·       It contributes 60% to the country's gdp.
·       It is a form of trade
·       it is the basis for many industries

There is conventional agriculture and sustainable agriculture (agro-ecology).
Conventional agriculture, most commonly practiced in the United States, usually involves the following criteria:
  • Altering or changing the natural environment (removing trees, tilling the soil, installing an irrigation system, etc.
  • Mono-cropping or planting one crop (ex: only corn is grown in a plot).
  • The crops grown are nonrenewable- after harvesting, the plot is bare again and requires cultivation (tilling and plowing of the soil), fertilization, planting, irrigation (watering), and harvesting all over again.
  • Using insecticides and pesticides to keep insects and animals from eating the crops; these chemicals are not only poisonous to insects, animals and humans, they also pollute ground water, streams, rivers, and oceans. 
  • Using inorganic fertilizers to provide nutrients to the soil.
  • A lot of energy and work for the farmer to maintain this unnatural farming system; nature is more aligned with diversity (it wants to be wild), rather than controlled and uniform. 
Sustainable agriculture (agro-ecology) uses ecological principles to farm, hence the prefix agro- to farm and ecology- the science of the relationship between organisms and their environments.  Agro-ecology involves:
  • Maintaining the natural environment and using ecological principles for sustained farming practices.
  • Poly-cropping or planting many crops together (ex: planting rows of corn, bean, and squash together rather than in separate plots, like in mono-cropping).
  • Since many plants are planted together, and each one has a different harvesting period, the plot is never bare.  This reduces soil erosion.
  • A diverse system of plants may attract several species of herbivores.  Some of these herbivores like to eat specific kinds of plants.  Predator species usually do not have a preference for which herbivores to eat.  This predation keeps the herbivore population in check, thus reducing predation of any one crop.
  • Nutrients from each intercrop plant provide different nutrients to the soil, thus increasing its fertility (ability to sustain life).
  • Less energy is required from the farmer because the agriculture system sustains itself.


        "Environment is surrounding atmosphere/ condition for existence" - "Environment is an essential natural process or an outcome of occurrence" – "Environment is of two types, one is negative and the other is positive":          

       Environment is so necessary because-
   Our life-support system's health is maintained by all the species that make-up the biosphere—from the smallest to the largest (our biodiversity). The survival of all these species is interconnected and dependent on each other. Bacteria and insects break down organic material to produce soil and nutrients so plants can grow. Plants provide oxygen and food for animals and many other benefits. Bees, other insects, and animals pollinate the plants so they can reproduce and keep the cycle going. They also maintain the health of plants and spread their seeds. The actual processes that take place between species and the environment are extremely complex and vulnerable. If humanity causes the extinction of one species—it's really the extinction of many species and the decline of our life-support system for us and future generations. God's gift must not be taken for granted—it must be cared for. If not, humanity will face the grim consequences of its actions. Biodiversity provides problem-solving raw materials for shelter and useful products, creates medicines, and allows us to pollinate and maintain healthy crops from being infested with harmful insects and diseases (without the need or hazards of chemicals or genetic engineering, which kill beneficial insects, additional wildlife, and plants). Although tropical forests contain some of the highest concentration of biodiversity on the planet, we destructively log more than 10 million acres of these forests each year (that’s approximately the size of a football field every 4 seconds) and efforts to promote sustainable forestry are largely failing.2 Scientists agree that the best way to protect biodiversity is to protect and maintain habitat large enough to accommodate a healthy ecosystem—tolerating small fragmented habitats will not preserve ecosystems or their biodiversity. In addition to nature providing us with penicillin, aspirin, morphine, and steroids; the medicine Taxol, which fights breast and ovarian cancer, comes from the bark of the pacific yew tree; the foxglove plant provides the drug digitalis which boosts the pumping action of weak hearts; and the rosy periwinkle plant is used to fight Hodgkin’s disease and childhood leukemia. Other candidates providing promising medicines include deep-sea sponges, tropical cone snails, dogfish sharks, the bark of the Holarrhena tree (found in Asia and Africa), and the plant Chonemorpha macrophylla (located in the foothills of the Himalayas). A microbe found in the hot springs of Yellowstone

The components of the environment are:

(1) Abiotic components
(2) Biotic components
It has three parts:
a) Atmosphere b) hydrosphere c) lithosphere d) biosphere

It has three parts:
a) Producer b) consumer c) de-composer
Agriculture and environment are closely connected each other. Both are most important for the existence of human being. If one is disordered then other is severely affected. So it’s very important for us to keep both environment and agriculture on the real track. Now I m going to describe effect of agriculture on the environment.
Effect of agriculture on the environment
 The effect of agriculture on the environment may be positive or may be negative .But we see negative effect more than we see positive effect.
Negative effects of agriculture on the environment are-
1.      Water pollution
2.      Air pollution
3.      Loss of wildlife
4.      Habitat and landscape features
5.      Soil degradation
6.      Ground water depletion.
1.      Water pollution:
Water of pond, lake, rivers is polluted by agricultural use of pesticide and fertilizer. Farming is currently a significant source of water pollution, which is a particular problem in certain regions of Europe and the United States, and at a local level in other countries of Asia pacific region. The application of fertilizers in agriculture and animal effluent from livestock account for as much as40% of nitrogen and 30% of phosphate emissions in surface water in some countries, contributing significantly to the problems of eutrophication which results in the depletion of oxygen in water. Pesticide run-off from agricultural land also impairs drinking-water quality and harms water-based wildlife.

                   People using pesticide and also fertilizer for their production but the rain water washed away some parts of pesticide and fertilizer to the river, lake and pond. So water of these sources is polluted by pesticide and fertilizer.

2. Air pollution:

Air pollution problems caused by ammonia (acid rain), methyl bromide (ozone depletion), pesticide drift, and crop burning and offensive odors also tend to be pronounced in areas of intensive agricultural production. Gaseous emissions from agriculture – in particular methane and nitrous oxide – are also a notable contributing factor to global warming and climate change. It is estimated that agriculture currently accounts for around 12.5% of total  greenhouse gas emissions although certain agricultural activities have a potentially significant mitigating effect on the process of global warming, particularly the sequestration of atmospheric carbon in the soil and the production of biomass crops, including those grown for energy use. In the longer term, climate change affects agriculture through the levels and variability of temperature and rainfall, which in turn leads to pressures to adjust farm practices and location, and commodities produced.
Agriculture has been identified as a significant cause of the loss of biodiversity.
3. Loss of wildlife:

    Many environmental experts are pessimistic about the future of our planet, especially the wildlife extinction.  Reality shows clearly to us that the number of animal living in our planet is decreasing because of different agricultural reasons. These reasons are given below.

                                I.      People are cutting trees for agricultural land so the animals of forest are being threatened as example we say sunderban of Bangladesh.
                             II.      People are using pesticide and fertilizer for more production but it is very harmful for some of the sects which are very important for agriculture. Pesticide is killing all types of insects.
                           III.      Pesticide and fertilizer are used by the farmers are polluting water so the animals of water are killed randomly. 
4.      Habitat and landscape features
            Pressures on land use and the adoption of more intensive farming practices, as well as land abandonment in some countries have led to concerns relating to the preservation of landscapes associated  with traditional agricultural practices, particularly in European countries, Japan and Korea, where such landscapes are generally considered to be of cultural significance. In other countries, such as Australia, New Zealand and North America, Asia-pacific
the preservation of rural landscapes is generally not considered a priority for government financial assistance, although there are concerns relating to the loss of rural land to urban development in certain areas, particularly in regions of the United States, and to rural depopulation in Australia. 
5.  Soil degradation:
      Soil degradation is on the increase worldwide, especially in the countries within the tropics. Mismanagement of arable areas by farmers and grazing areas by livestock owners is one of the major causes of soil degradation. More sustainable management of lands would reduce environmental pressures. Conservation tillage, i.e. reduced or no tillage, is the key to sustainable arable land management as it protects the soil resources, increases the efficiency of water use and, of special importance in semi-arid areas, reduces the effects of droughts
Erosion is strongly related to human activity. For example, roads which increase impermeable surfaces lead to streaming and ground loss. Agriculture also accelerates soil erosion (increase of field size, correlated to hedges and ditches removal). Meadows are in regression to the profit of plowed lands. Spring cultures (sunflower, corn, and beet) surfaces are increasing and leave the ground naked in winter. Sloping grounds are gradually colonized by vine. Lastly, use of herbicides leaves the ground naked between each crop. Fertilization by mineral manures rather than organic manure gradually destructure the soil. Many scientists observed a gradual decrease of soil organic matter content in soils, as well as a decrease of soil biological activity (in particular, in relation to chemical uses). Lastly, deforestation, in particular, is responsible for degradation of forest soils.
Agriculture increases the risk of erosion through its disturbance of vegetation by way of:
  • Overgrazing of animals.
  • Planting of a monoculture.
  • Row cropping.
  • Tilling or plowing.
  • Crop removal.
  • Land-use conversion.
Wind erosion is caused by the action of the wind on the soil surface and is the process by which fine soil particles are carried away. It affects agricultural land in much of northern Africa and the Near East, parts of southern, central and eastern Asia, Australia, North West China, southern South America and North America. The severity of wind erosion is influenced by wind speed, the condition of the soil surface and the amount of vegetation cover present. Like water erosion, wind erosion is significantly influenced by the amount of vegetation cover, therefore any activity that removes vegetation, such as agriculture, deforestation or other land degradation processes, can result in severe wind erosion.

6. Ground water depletion:

The importance of groundwater for the existence of human society cannot be overemphasized. Groundwater is the major source of drinking water in for the people. Besides, it is an important source of water for the agricultural and the industrial sector. Being an important and integral part of the hydrological cycle, its availability depends on the rainfall and recharge conditions. Till recently it had been considered a dependable source of uncontaminated water.
Water can be depleted because of-

    1. Farmers use ground water for irrigation.
    2. Lack of adequate attention to water conservation.
    3. Lack of efficiency in water use.
    4. An uncontrolled use of the borewell technology.
Positive effects of agriculture on the environment

Agriculture has some positive effects on the environment those are given below-

  1. Contribution to water accumulation and flood control.
  2. Nutrient recycling and fixation.
  3. Soil formation.
  4. Carbon sequestration by trees and soil.
  5. Wildlife and biodiversity protection.
      6.    The provision of recreational services and aesthetic value.

The impact of environmental change on the agriculture

     Environmental change and agriculture are interrelated processes, both of which take place on a global scale. Global warming is projected to have significant impacts on conditions affecting agriculture, including temperature, precipitation and glacial run-off. These conditions determine the carrying capacity of the biosphere to produce enough food for the human population and domesticated animals. Rising carbon dioxide levels would also have effects, both detrimental and beneficial, on crop yields. The overall effect of environmental change on agriculture will depend on the balance of these effects. Assessment of the effects of global climate changes on agriculture might help to properly anticipate and adapt farming to maximize agricultural production.
At the same time, agriculture has been shown to produce significant effects on climate change, primarily through the production and release of greenhouse gases such as carbon dioxide, methane, and nitrous oxide, but also by altering the earth's land cover, which can change its ability to absorb or reflect heat and light, thus contributing to radioactive forcing. Land use change such as deforestation and desertification, together with use of fossil fuels, are the major anthropogenic sources of carbon dioxide; agriculture itself is the major contributor to increasing methane and nitrous oxide concentrations in earth's atmosphere.

Despite technological advances, such as improved varieties, genetically modified organisms, and irrigation systems, weather is still a key factor in agricultural productivity, as well as soil properties and natural communities. The effect of climate on agriculture is related to variability’s in local climates rather than in global climate patterns. The earth's average surface temperature has increased by 1 degree F in just over the last century. Consequently, agronomists consider any assessment has to be individually considering each local area.
On the other hand, agricultural trade has grown in recent years, and now provides significant amounts of food, on a national level to major importing countries, as well as comfortable income to exporting ones. The international aspect of trade and security in terms of food implies the need to also consider the effects of climate change on a global scale.
A study published in Science suggest that, due to climate change, "southern Africa could lose more than 30% of its main crop, maize, by 2030. In South Asia losses of many regional staples, such as rice, millet and maize could top 10%".

Climate change induced by increasing greenhouse gases is likely to affect crops differently from region to region. For example, average crop yield is expected to drop down to 50% in Pakistan according to the UKMO scenario whereas corn production in Europe is expected to grow up to 25% in optimum hydrologic conditions.
More favorable effects on yield tend to depend to a large extent on realization of the potentially beneficial effects of carbon dioxide on crop growth and increase of efficiency in water use. Decrease in potential yields is likely to be caused by shortening of the growing period, decrease in water availability and poor vernalization.

In the long run, the environmental change could affect agriculture in several ways:
  • Productivity, in terms of quantity and quality of crops.
  • Agricultural practices, through changes of water use (irrigation) and agricultural inputs such as herbicides, insecticides and fertilizers.
  • Environmental effects, in particular in relation of frequency and intensity of soil drainage (leading to nitrogen leaching), soil erosion, reduction of crop diversity.
  • Rural space, through the loss and gain of cultivated lands, land speculation, land renunciation, and hydraulic amenities.
  • Adaptation, organisms may become more or less competitive, as well as humans may develop urgency to develop more competitive organisms, such as flood resistant or salt resistant varieties of rice.
       Most agronomists believe that agricultural production will be mostly affected by the severity and pace of climate change, not so much by gradual trends in climate. If change is gradual, there may be enough time for biota adjustment. Rapid climate change, however, could harm agriculture in many countries, especially those that are already suffering from rather poor soil and climate conditions, because there is less time for optimum natural selection and adaptation

Some other impacts of environmental change on agriculture are given below-

  • Shortage in grain production
        Between 1996 and 2003, grain production has stabilized slightly over 1800 millions of tons. In 2000, 2001, 2002 and 2003, grain stocks have been dropping, resulting in a global grain harvest that was short of consumption by 93 millions of tons in 2003.

  • Poverty impacts
Researchers at the Overseas Development Institute (ODI) have investigated the potential impacts climate change could have on agriculture, and how this would affect attempts at alleviating poverty in the developing world.

·        Temperature potential effect on growing period

      . An increase in temperature will speed up development. In the case of an annual crop, the duration between sowing and harvesting will shorten (for example, the duration in order to harvest corn could shorten between one and four weeks). The shortening of such a cycle could have an adverse effect on productivity because senescence would occur sooner.
·        Potential effect of atmospheric carbon dioxide on yield
    Carbon dioxide is essential to plant growth. Rising CO2 concentration in the atmosphere can have both positive and negative consequences. Increased CO2 is expected to have positive physiological effects by increasing the rate of photosynthesis. Currently, the amount of carbon dioxide in the atmosphere is 380 parts per million. In comparison, the amount of oxygen is 210,000 ppm. This means that often plants may be starved of carbon dioxide, being outnumbered by the photosynthetic pollutant oxygen. The effects of an increase in carbon dioxide would be higher on C3 crops (such as wheat) than on C4 crops (such as maize), because the former is more susceptible to carbon dioxide shortage.

·        Climate changes and Agricultural surfaces

Climate change may increase the amount of arable land in high-latitude region by reduction of the amount of frozen lands. A 2005 study reports that temperature in Siberia has increased three degree Celsius in average since 1960 (much more than the rest of the world).[12] However, reports about the impact of global warming on Russian agriculture[13] indicate conflicting probable effects : while they expect a northward extension of farmable lands,[14] they also warn of possible productivity losses and increased risk of drought.[15]
Low lying areas such as Bangladesh, India and Vietnam will experience major loss of rice crop if sea levels are expected to rise by the end of the century. Vietnam for example relies heavily on its southern tip, where the Mekong Delta lies, for rice planting. Any rise in sea level of no more than a meter will drown several sq. km. of rice paddies, rendering Vietnam incapable of producing its main staple and export of rice.[16]

·        Erosion and fertility

           With global warming, soil degradation is more likely to occur, and soil fertility would probably be affected by global warming. However, because the ratio of carbon to nitrogen is a constant, a doubling of carbon is likely to imply a higher storage of nitrogen in soils as nitrates, thus providing higher fertilizing elements for plants, providing better yields. The average needs for nitrogen could decrease, and give the opportunity of changing often costly fertilization strategies.

·        Ozone and UV-B

Some scientists think agriculture could be affected by any decrease in stratospheric ozone, which could increase biologically dangerous ultraviolet radiation B. Excess ultraviolet radiation B can directly effect plant physiology and cause massive amounts of mutations, and indirectly through changed pollinator behavior, though such changes are simple to quantify
  • Increasing temperature and Water scarcity

                 Because of environmental change the temperature of whole world is rising. So we are facing water scarcity and many lands are turned into dry land .For our agriculture production. People are using more ground water and surface water for irrigation.

Some recommendations for both ‘agriculture and its impact on the environment’ and ‘change of environment and its effect on agriculture’ are given below

  • Using environmental friendly fertilizer for the production that will help to increase fertility of the land so the production will be increased.
  • Reducing cutting of trees to protect the environment from different hazard.
  • Re used industrial waste for protecting water pollution
  • Managing tree plantation.
  • Using more surface water than underground water.
  • Using environmental friendly technology.
  • Managing water reuse system.
       Agriculture and environment are closely connected. Agriculture has both negative and positive effect on the environment. The most important thing that the use of fertilizer and pesticide which is very important for good crops production. So we should be careful to use both of these. As possible we should use environmental friendly fertilizer. For human activities environment are badly affected and that has bad effect to the agriculture. It is reducing our production as well as reducing our rainfall, increasing temperature which is very dangerous for agriculture. For both environmental impact and also agricultural impact we have to be more careful so we will be able to make a good environment as well as good agricultural production with safely.

History of Agriculture

History of Agriculture
Since its development roughly 10,000 years ago, agriculture has expanded vastly in geographical coverage and yields. Throughout this expansion, new technologies and new crops were integrated. Agricultural practices such as irrigation, crop rotation, fertilizers, and pesticides were developed long ago, but have made great strides in the past century. The history of agriculture has played a major role in human history, as agricultural progress has been a crucial factor in worldwide socio-economic change. Wealth-concentration and militaristic specializations rarely seen in hunter-gatherer cultures are commonplace in societies which practice agriculture. So, too, are arts such as epic literature and monumental architecture, as well as codified legal systems. When farmers became capable of producing food beyond the needs of their own families, others in their society were freed to devote themselves to projects other than food acquisition. Historians and anthropologists have long argued that the development of agriculture made civilization possible.


Agriculture has played a key role in the development of human civilization. Until the Industrial Revolution, the vast majority of the human population labored in agriculture. Development of agricultural techniques has steadily increased agricultural productivity, and the widespread diffusion of these techniques during a time period is often called an agricultural revolution. A remarkable shift in agricultural practices has occurred over the past century in response to new technologies. In particular, the Haber-Bosch method for synthesizing ammonium nitrate made the traditional practice of recycling nutrients with crop rotation and animal manure less necessary
Synthetic nitrogen, along with mined rock phosphate, pesticides and mechanization, have greatly increased crop yields in the early 20th century. Increased supply of grains has led to cheaper livestock as well. Further, global yield increases were experienced later in the 20th century when high-yield varieties of common staple grains such as rice, wheat, and corn (maize) were introduced as a part of the Green Revolution. The Green Revolution exported the technologies (including pesticides and synthetic nitrogen) of the developed world out to the developing world. Thomas Malthus famously predicted that the Earth would not be able to support its growing population, but technologies such as the Green Revolution have allowed the world to produce a surplus of food
The percent of the human population working in agriculture has decreased over time.    

Meanings of Agriculture

Agriculture refers to the production of food and goods through farming and forestry. Agriculture was the key development that led to the rise of civilization, with the husbandry of domesticated animals and plants (i.e. crops) creating food surpluses that enabled the development of more densely populated and stratified societies. The study of agriculture is known as agricultural science (the related practice of gardening is studied in horticulture).
Agriculture encompasses a wide variety of specialties. Cultivation of crops on arable land and the pastoral herding of livestock on rangeland remain at the foundation of agriculture. In the past century a distinction has been made between sustainable agriculture (e.g. permaculture or organic agriculture) and intensive farming (e.g. industrial agriculture).
Modern agronomy, plant breeding, pesticides and fertilizers, and technological improvements have sharply increased yields from cultivation, and at the same time have caused widespread ecological damage and negative human health effects. Selective breeding and modern practices in animal husbandry such as intensive pig farming (and similar practices applied to the chicken) have similarly increased the output of meat, but have raised concerns about animal cruelty and the health effects of the antibiotics, growth hormones, and other chemicals commonly used in industrial meat production.
The major agricultural products can be broadly grouped into foods, fibers, fuels, raw materials, pharmaceuticals and illegal drugs, and an assortment of ornamental or exotic products. In the 2000s, plants have been used to grow biofuels, biopharmaceuticals, bioplastics,[1] and pharmaceuticals.[2] Specific foods include cereals, vegetables, fruits, and meat. Fibers include cotton, wool, hemp, silk and flax. Raw materials include lumber and bamboo. Drugs include tobacco, alcohol, opium, cocaine,and digitalis. Other useful materials are produced by plants, such as resins. Biofuels include methane from biomass, ethanol, and biodiesel. Cut flowers, nursery plants, tropical fish and birds for the pet trade are some of the ornamental products.
In 2007, about one third of the world's workers were employed in agriculture. However, the relative significance of farming has dropped steadily since the beginning of industrialization, and in 2003 – for the first time in history – the services sector overtook agriculture as the economic sector employing the most people worldwide.[3] Despite the fact that agriculture employs over one-third of the world's population, agricultural production accounts for less than five percent of the gross world product (an aggregate of all gross domestic products.

Waste Water Usage

Waste Water Use in Agriculture


With increasing global population, the gap between the supply and demand for water is widening and is reaching such alarming levels that in some parts of the world it is posing a threat to human existence. Scientists around the globe are working on new ways of conserving water. It is an opportune time, to refocus on one of the ways to recycle water—through the reuse of urban wastewater, for irrigation and other purposes. This could release clean water for use in other sectors that need fresh water and provide water to sectors that can utilize wastewater e.g., for irrigation and other ecosystem services. In general, wastewater comprises liquid wastes generated by households, industry, commercial sources, as a result of daily usage, production, and consumption activities. Municipal treatment facilities are designed to treat raw wastewater to produce a liquid effluent of suitable quality that can be disposed to the natural surface waters with minimum impact on human health or the environment. The disposal of wastewater is a major problem faced by municipalities, particularly in the case of large metropolitan areas, with limited space for land-based treatment and disposal. On the other hand, wastewater is also a resource that can be applied for productive uses since wastewater contains nutrients that have the potential for use in agriculture, aquaculture, and other activities.
In both developed and developing countries, the most prevalent practice is the application of municipal wastewater (both treated and untreated) to land. In developed countries where environmental standards are applied, much of the wastewater is treated prior to use for irrigation of fodder, fiber, and seed crops and, to a limited extent, for the irrigation of orchards, vineyards, and other crops. Other important uses of wastewater include, recharge of groundwater, landscaping (golf courses, freeways, playgrounds, schoolyards, and parks), industry, construction, dust control, wildlife habitat improvement and aquaculture. In developing countries, though standards are set, these are not always strictly adhered to. Wastewater, in its untreated form, is widely used for agriculture and aquaculture and has been the practice for centuries in countries such as China, India and Mexico.
Thus, wastewater can be considered as both a resource and a problem. Wastewater and its nutrient content can be used extensively for irrigation and other ecosystem services. Its reuse can deliver positive benefits to the farming community, society, and municipalities. However, wastewater reuse also exacts negative externality effects on humans and ecological systems, which need to be identified and assessed.
Before one can endorse wastewater irrigation as a means of increasing water supply for agriculture, a thorough analysis must be undertaken from an economic perspective as well. In this regard the comprehensive costs and benefits of such wastewater reuse should be evaluated. Conventional cost benefit analysis quite often fails to quantify and monetize externalities associated with wastewater reuse. Hence, environmental valuation techniques and other related tools should be employed to guide decision-making. Moreover, the economic effects of wastewater irrigation need to be evaluated not only from the social, economic, and ecological standpoint, but also from the sustainable development perspective.
Pakistan is a case which illustrates this problem. Both treated and untreated municipal wastewater in the vicinity of large cities like Faisalabad is used for vegetable production. But, how safe is this practice? How does one tradeoff between the obvious benefits of this use and the costs associated with it?
1 Sources of Wastewater
In general, municipal wastewater is made up of domestic wastewater, industrial wastewater, storm water, and by groundwater seepage entering the municipal sewage network. Domestic wastewater consists of effluent discharges from households, institutions, and commercial buildings. Industrial wastewater is the effluent discharged by manufacturing units and food processing plants. In Faisalabad, a large proportion of municipal wastewater from some sections of the city consists of industrial wastewater discharges. Unlike in some developed cities where the systems are separate, here, the municipal sewage network also serves as the storm water sewer. Due to defects in the sewerage system, there is groundwater seepage as well, adding to the volume of sewage to be disposed.
2 Characteristics of Wastewater flow
In general, domestic wastewater entering municipal wastewater systems tend to follow a diurnal pattern (Asano et al. 1985). This flow is low during the early morning hours and a first peak generally occurs in the late morning followed by a second peak in the evening—after dinner hour. However, the ratio of peak flow loads to average flow is likely to vary inversely with the size of the community and the length of sewer system. Peak flows may also be generated during festive occasions, and at times of religious rituals, such as the Friday prayer in Pakistan, during business hours, tourist seasons, and in areas with large university campuses etc.
Industrial wastewater flows, closely follow the processing pattern of local industries, which depend on the processes involved, the number of shifts operated, and the water requirement of the industry. Variations from established patterns are minimal and occur during shift changes or stoppages. Flow variations may also occur due to processing of seasonal products. Therefore, seasonal fluctuations in the industrial wastewater discharges are more significant. In cities where, industrial wastewater constitutes a major component of the total municipal wastewater flow, fluctuations in industrial wastewater discharges are likely to be of significant importance in water cycle management.
In developed economies, per capita wastewater generation is largely determined by economic factors and reliability of water supply. However, in a developing country like Pakistan, where water supplies are rationed, availability is uncertain, and since water is not priced at its true opportunity cost, per capita wastewater generation may largely be a function of availability and minimum usage requirements.
3 Composition of Wastewater
Though the actual composition of wastewater may differ from community to community, all municipal wastewater contains the following broad groupings of constituents:
                        Organic matter
                        Nutrients (Nitrogen, Phosphorus, Potassium)
                        Inorganic matter (dissolved minerals)
                        Toxic chemicals
The final composition of raw wastewater depends on the source and its characteristics. In the case of mixed municipal wastewater this depends on the types and numbers of industrial units and the characteristics of the residential communities. The composition of typical raw wastewater for selected countries is given in table 2.

Table 2. Composition of raw wastewater.

 Composition of raw wastewater (mg/l)



Existing Approaches for Regulating Wastewater Reuse in Agriculture
Wastewater contains high concentrations of excreted pathogens such as viruses, bacteria, helminths eggs, and fecal coliforms. These excreted pathogens have the potential to cause disease if present in a human host in sufficient quantities. Intestinal nematodes pose the highest degree of risk of infection while bacteria pose a lower risk. Viruses exhibit the lowest risk. To minimize the potential risk of infection, the World Bank, World Health Organization and International Reference Centre for Waste Disposal at Engelberg, Switzerland, convened a group of experts comprising of epidemiologists, social scientists and sanitary engineers in 1985, to review recent epidemiological evidence, and make recommendations. This report was the basis for the WHO guidelines on the safe use of water for agriculture and aquaculture. The rationale behind the WHO guidelines outlined below, was to develop criteria that would prevent the transmission of communicable diseases while optimizing resource conservation and recycling.