>> ENVIRONMENTAL ISSUES
>> Agricultural Activities
Agriculture and Environment are related in many ways. On one hand agriculture demands good environmental quality. On the other hand, agriculture is a major cause of habitat loss, extensive water use, eutrophication, waste product and a source of large-scale atmospheric emissions of methane. With an increase in the global population, the need arises for increased agricultural production through higher yields, higher cropping intensities (the number of times an area of land is cropped in one year) and through an increase in the arabal areas.
Two major sources of pollution arise from agricultural activities. Direct pollution due to the intensification of agriculture while indirect pollution arising from major changes in land use as follows:
Direct pollution due to the intensification of agriculture:
- Nutrients: Intensive agriculture can be achieved with fertilizer amounts of 250-300 kg/ha increasing yields two or three folds. High loading of more than 500kg/ha of fertilizer or lower amounts on soils which do not retain nutrients very well cause problems.
- Water logging and Salinization: Artificial irrigation has been regarded as the solution for limited resources of agricultural land. With irrigation water salts are added to the soils and left behind as water evaporates thus causing salinization while water logging is caused by a rise of the water table.
- Pesticides: The use of pesticides has almost doubled every ten years since 1945 to combat pests and weeds and reduce losses. With significant losses caused to crops after the harvest by a multitude of pests attacking the stored products.
- Agricultural wastes: Wastes from crops such as straw, leaves and roots are a considerable part of the total primary production while organic wastes arise from livestock rearing.
Indirect pollution arising from major changes in land:
- Deforestation: It is expected that most of the extra land area which will be needed in the next decade to satisfy human needs such as agricultural land and fuel-wood will have to be transferred from tropical forests. However, many tropical forest soils are unsuitable for continuous cultivation and soil fertility cannot be maintained.
- Soil degradation: The removal of vegetation leads to a rapid decay of organic matter, destruction of soil organisms, loss of soil fertility, soil erosion, irreversible hardening of the soil and increased acidity.
- Desertification: In the past, climatic fluctuations resulted in the expansion and contraction of deserts. Today, humans through overgrazing, bush fires, expansion of agricultural crops and deforestation cause most desertification. Mismanagement of resources is considered to be responsible for over 80 % of recent worldwide desertification.
- Erosion: Most, if not all of the world's agricultural areas are susceptible to erosion by wind and water with wind erosion being more serious in arid and semi-arid regions.
- Wetland exploitation: The greatest wetland losses have occurred as a result of agricultural conversion.
Pollution from agricultural activities and indirect agricultural effects has markedly influenced the landscape and the environment world wide and in tern human health.
The growth of unsustainable intensive agriculture has given rise to many problems as follows:
- Natural global cycles of the most important nutrient phosphorus (P) and nitrogen (N) are disturbed due to the agricultural nutrient regime. Over loading with fertilizer nutrients of more than 500kg/ha contributes towards eutrophication, nitrate accumulation in ground water, acidificaton of soil and emission of the green house gas nitrous oxide N2O. While lower a mount on soils which do not retain nutrients very well leads to losses through excessive nutrient supply.
- Water logging and salinization are lowering the productivity of one quarter of the worlds irrigated cropland. Irrigation systems worldwide have an efficiency of 30 to 50% as a result of water logging, salinization, alkalinization, leakage of transport systems, infiltration, run-off, eutrophication of reservoirs and other factors.
- The application of pesticides not only kills pests but also their predators, parasites and pollinating insects of the crop, thereby disturbing the natural regulating mechanism. Another problem encountered is the increasing development of resistance species to pesticides starting a vicious cycle of repeated applications with higher dosage and the development of persistent pesticides leading to more resistance species. Other effects extend beyond agricultural systems through the transportation of pesticides by wind and water resulting in long-term soil and ground water contamination.
- Agricultural wastes from crops when they are ploughed, composted or burned on land produce CO2 and nitrogen oxides thus contributing to the global greenhouse effect. On the other hand if wastes are dredged anaerobically such as straw in paddy fields or waste in land fills the carbon is released as methane CH4 that is 24 times more reactive as a green-house gas than CO2 while the nitrogen is released as nitrous oxide. Other effects include sever local water pollution from the discharge of waste due to the processing of agricultural crops.
Major changes in land use has given rise to many problems as follows:
- Deforestation may influence the frequency of rainfall and promote erosion during heavy rainfall with mud floods causing siltation of downstream areas thus effecting mangroves and coral reefs and consiquencilly damaging fisheries. Deforestation also influences the climate and the CO2 content of the atmosphere through felling and burning of forests while loosing a large amount of photosynthetic activity that results in O2 production in large amounts.
- Soil degradation damages agriculture and forest productivity thus disturbing the hydrological cycle, which leads to increases in the frequency and severity of floods and droughts.
- In the past, climatic fluctuations resulted in the expansion and contraction of deserts. Today, humans through overgrazing, bush fires, expansion of agricultural crops and deforestation cause most desertification. Mismanagement of resources is considered to be responsible for over 80 % of recent worldwide desertification.
- Soil erosion could reduce agricultural production and transport substantial amount of the N-fertilizer from fertile soils to sediments in areas of intensive agriculture in addition to increasing siltation in waterways, lakes and reservoirs thus disturbing navigation, irrigation, power generation and hampering water discharge.
- Wetland exploitation causes their disappearance and results in a significant loss of the local natural water purification capacity in addition to losing the regulative effect of the wetland birds on insect pests.
Due to the strong mutual dependency of agriculture and environment, the integration of environmental aspects in agricultural projects is urgently needed through:
- Stimulating sustainable agricultural practices, taking in to consideration long-term productivity over short-term benefits through education.
- Stimulate alternative and traditional agricultural procedures that are less productive in the short-term but more sustainable in the long term and less polluting.
- Preventing the over use of fertilizers by application methods that reduce leaching, denitrification and nitrification. Using analytical techniques to better adapt to the actual needs of the crop.
- Recycling of organic wastes, using biological nitrogen fixation and anti-erosion measures to prevent exhaustion, soil and structure loss.
- Mitigation of direct pollution by waste treatment through the controlled use of biogasification and the prevention of heavy metal contamination of organic wastes has to be encouraged, ahead of incineration and landfills.
- Proper assessment of the carrying capacity of the soil before any irrigation projects. As well as detailed local assessments to cover specific conditions of climate, soil, type of crop and pest, cultural traditions and possible skills.
- Integrated Pest Management Approach through education and research, in addition to an internationally harmonized methodology for environmental impact assessment of pesticides, taking account of persistence, mobility, bioaccumulation and ecotoxicity in generally modeled systems in line with the international code of conduct.
- Deforestation for an unsustainable agriculture should be stopped by international recognition of the global value of forests and appropriate reforestation initiated.
- Desertification needs to be controlled remote sensing techniques for monitoring should be supported to increase the awareness.
UNEP 1992. Chemical Pollution: A Global Overview