Impact of Air Pollution (SMOG) on Crop Plants

Source: Pavel., C and L. Sefrna.2001.Air pollution impact on crop production, Charless University In Prague, Acta Universitatis Carolinae .No.2,Page 49-62. www.dawn.com/

Agricultural practices in both the developed and developing countries have always aimed to eliminate or minimize the numerous constraints on producing maximum yield of crops. These constraints may be A-biotic, including nutrient deficiency, metal toxicity, salinity, drought, low and high temperatures, wind and water logging. There are also numerous biotic constrains: invertebrates and vertebrates pests; fungal, viral and bacterial pathogens and trampling. Although vast sums of money are spent on overcoming these, there is another constraint that receives much less attention, but with evidence that it is potentially a widespread threat to crop production - air pollution Smog, also known as ground-level ozone, is a thick yellowish black fog which suspends in the air. The extent of the damage to plants is subject to the pollutant concentration in the air, exposition length and other environmental factors including light, heat, relative humidity, CO2 concentration, soil humidity and nutrition
In recent years, there has been a decline in interest in effects of air pollution on crops in the developed countries, doubtless largely due to overproduction. The developing countries are certainly not characterized by overproduction, with most countries striving desperately to increase yield of their staple crops to feed rapidly expanding populations. Air pollution has traditionally been viewed as a problem of Western countries, where the bulk of the industry and motor vehicles responsible for the major pollutants residues. However, emissions of some of these pollutants are being reduced as a result of introduction of stringent controls in recognition of their adverse effects on health, vegetation, aquatic ecosystems and materials, as well as a decline of polluting heavy industries. The latter are in fact transferring to the developing world, where rapid industrialization is taking place in many countries but with poor emission controls.
At the same time motor traffic is growing at an enormous rate in the developing world, often using old and poorly maintained vehicles that play a major role in contributing to deterioration in air quality. Thus Sulphur Dioxide (SO2) and Nitrous Oxide (NO) are increasing rapidly in many developing countries. We know far less about the third ubiquitous pollutant, O3 because very little monitoring has been carried out in most countries, and most of this is restricted to the cities where concentrations are normally lower than in adjacent agricultural areas.
The Met Office has released a weather warning describing the smog comprising nitrogen oxide, carbon monoxide, sulphur dioxide and other aerosols as a result of cold high pressure in the upper atmosphere. Suspended matter accumulates in the lower atmosphere, colliding with water vapor which causes a chain reaction that produces smog. Air pollution injury to plants can be evident in several ways. Injury to foliage may be visible in a short time and appear as necrotic lesions (dead tissue), or it can develop slowly as a yellowing or chlorosis of the leaf. There may be a reduction in growth of various portions of a plant. Plants may be killed outright, but they usually do not succumb until they have suffered recurrent injury.
Agricultural crops can be injured when exposed to high concentrations of various air pollutants. Injury ranges from visible markings on the foliage, to reduced growth and yield, to premature death of the plant. The development and severity of the injury depends not only on the concentration of the particular pollutant, but also on a number of other factors. These include the length of exposure to the pollutant, the plant species and its stage of development as well as the environmental factors conducive to a build-up of the pollutant and to the preconditioning of the plant, which make it either susceptible or resistant to injury.
There are two major ways in which air pollutants may damage agricultural production:

Direct Influence of the Pollutants

By the direct influence the pollutants particles can block up stomata or collect on plant cuticle. Reaction of the plants against air pollutant influence depends mainly on light, temperature, CO2 concentration, humidity and nutrients accessibility, vegetation period, etc. Some pollutants SO2, Suspended particulate matter (SPM), NO2 and O3 may cause a visible damage to plant's leaves or needles, disturb their physiologic processes and reduce their growth. The NO2 impact on the plants becomes evident especially in combination with other compounds.
The negative influence of air pollutants can develop with the agricultural crops by visible symptoms (chlorosis, necroses), by a total fall in growth, yields decrease and quality loss. A looses in agricultural production, as a result of air pollution, are usually estimated by mathematics models. Agricultural crops comprise many species (grain crops, fodder plants, fruit, vegetables, flowers) that can be used in miscellaneous ways.

Influence of Nitrogen Dioxide

Nitrogen dioxide is the cause of growth reduction and visible damage. Treshow (1970) observed visible damages at the concentrations ranging from 4 to 20 µg/m3. But these high NO2 concentrations in the open air are not presumable. According to Dempster and Manning (1988) research, a higher concentrations of NO2 existence results in increased plant perceptivity to parasites.

Influence of Sulphur Dioxide

Sulphur dioxide can reduce the growth of plants, biomass, and consequently the yields. Clover belongs to grass family and is most sensitive which reacts to sulphur dioxide pollution. Yields can be decreased by up to 30% at a constant SO2 impact has been observed with several crops. Treshow (1970) says that the Lucerne yields decrease, as a consequence of SO2 impact, was directly proportional to the quantity of necrotic spots on the leaves.

Influence of Ozone (O3)

The agricultural crops damage caused by ozone has been described with many crops, and it develops usually in the limitation of growth and biomass production and in yields decrease. Growth reduction can happen also without visible damage. Yield decrease due to O3 are visible changes on the plants and other ill effects have been described by many authors in many crops like tobacco plant, soya bean, beans, rye, wheat, potato, pumpkin, pea, lucerne and tomato.

Influence of Dust Aerosol

Relatively few data exist about dust aerosol (SPM) influence on agricultural crops. Dust aerosol produces a surface dust film on leaves and needles, which reduces falling solar radiation intensity, and consequently photosynthesis. Yields decrease can range from 5 to 10% and has been described in Germany.
Another kind of pollutants, which often appears in combination with ozone (they develop from the same precursors), is peroxyacetyl nitrates (PAN). Bunce (1991) mentions the toxic concentrations of ozone and PAN to be at 0.1 ppm. At this point the photosynthesis intensity already decreases two times.

Sowing Method

Most suitable method of sowing is drilling. Broad casting is usually done in dry regions. The seeds are sown at 2 cm depth with a plant to plant spacing of 8 -10 cm and 30 cm between rows. If the surface layers are dry this depth can be increased to 3 cm if the soil type is one which does not crust easily. The seedlings of mungbean can have a hard time breaking through a thick crust and stands will be reduced. Planting equipment for soybean, fieldbean and cowpea can be used to plant mungbean but careful adjustments must be made to properly deliver and distribute the small seeds. Populations of 150,000-200,000 plants per acre can be achieved.

Indirect Influence of Pollutant

Air pollutants may cause indirectly wide range of subtle physiological, chemical or anatomical changes which will not lead to detectable yield reductions under optimal growth conditions. These changes may increase the crop's sensitivity to other stresses, thereby contributing to significant yield losses. Exposure to sulphur dioxide and nitrogen dioxide, for example, consistently leads to increased growth rates of a range of aphid pests.
The indirect influence means degradation and contamination of soil, while its elimination leads to plant-growing costs increase or to land capability decrease. Soil degradation means the entire deterioration of physicochemical and biological soil character in comparison with original state where the mapping is more complicated than the ground cover mapping. The critical loading by acid deposition depends mainly on the buffering capacity of the soil, which is proportional to the velocity of minerals chemical weathering and soil capability. The principal degradation process caused by soil acidification impact is regarded to be leaching of basic K, Ca and Mg cations which causes nutrients deficit. The mobilization and concentration of toxic metals and aluminum are common elements of the soil mantle therefore they causes damage not only to plants but also the fauna of rivers/waterways and lakes.

Recent Situation in Pakistan

Recently Pakistan especially Lahore has experienced thick layers of fog in its short winter season. However, the fog that the city is used to is mere condensed water vapours suspended in the atmosphere.
In November, NASA explained cause of Smog in Pakistan. They reported that there are coal operated industries on the foothills of the Himalayas India. The pollutants generated from there are deflected from the mountains and as the wind blows from East to West, the polluted air enters Pakistan through the Khyber Pakhtunkhwa and Punjab area.
In places near irrigation canals, rice paddies and rivers where there is more moisture available, the fog gets even thicker. The smog only gets cleared when it rains, washing away the lower layers of the atmosphere where all the harmful gases and other pollutants are trapped near the ground. In the winter months, with delayed rainfall, the cold and continuously dry conditions concentrate all the pollutants in the lower levels of the atmosphere, causing the smog to spread all over the Punjab.
Though rainfall seems to be the answer to the current problem, but due to sulphur dioxide and nitrous oxide present in the atmosphere, if we receive light rainfall, it will be in the form acid rain which is dangerous for humans as well as crops. Therefore heavy rainfall is required to settle down pollutants suspended in the air.

Fertilizer

Mungbean is a legume. It has nodulation capability which can fix atmospheric nitrogen into the soil, if seed is inoculated with bio-fertilizer using inoculants developed for nodulation of mungbeans. High and effective nodulation on the roots of the mungbean is an important agronomic factor for enhanced productivity and fixation of atmospheric nitrogen into the soil. Fertilizer at the rate of 50kg or one bag of DAP can be broadcasted and incorporated into the soil before planting.

Irrigation

Mung bean is a short duration and drought tolerant crop therefore it requires less irrigation but to get maximum yield from irrigated areas 350 - 420 mm water is sufficient.

Harvesting and Yield

Pod maturity in mungbean is not uniform because the plants flower over an extended period. This makes it difficult to decide when to harvest. Generally harvest should begin when one half to two-thirds of the pods are mature. Seeds might be between 13%-15% moisture at this time. Swath the plants to allow further maturity of the pods and then threshed. This is an especially useful harvest system for the vine type varieties or when there is delayed maturity or problem weeds present. Swathing should be done earlier in the day to prevent severe shatter losses.

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