Effects of Air Pollution on Crops in Developing Countries

Agricultural practice in both the developed and developing world has always aimed to eliminate or minimize the numerous constraints on producing maximum yield of crops. These constraints may be abiotic, including nutrient deficiency, metal toxicity, salinity, drought, low and high temperatures, wind, and waterlogging. There are also numerous biotic constraints: invertebrate and vertebrate 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. As early as the 17th century, the noted English diarist John Evelyn (1661) described graphically the effects of the smoke ridden air of London on ornamental plants and fruit trees growing in the city. Research into this phenomenon that commenced in the late 19th century was initially concerned with trees near smelters in both Europe and North America.In the final three decades of the last century, this research mushroomed, with extensive programs in many parts of the developed world. Much of this research was aimed at understanding the effects on crop yield and growth of the ubiquitous primary pollutants, sulphur dioxide (S02), and nitrogen oxides (NOX), as well as the secondary pollutant ozone (03), indicating that all three pollutants were at different times and in different places having serious deleterious effects on crop productivity, with the two primary pollutants being associated mainly with industrial point sources and the urban fringe, whereas 03 was widespread at phytotoxic levels in rural areas. Subsequently interest also developed into the potential for air pollution to have indirect adverse effects on crops by exacerbating the impacts of familiar biotic stresses, such as pets and pathogens, and abiotic stresses, such as drought and frost.