Urban gardens are increasing the availability of fresh produce for city dwellers. They are also adding beauty to places where they are located and they provide both recreational and vocational opportunities for the gardeners involved. However, urban garden growers and planners are facing several challenges including soil pollution, water shortage and air pollution. The following discussion provides a brief description of these issues and suggestions on how to solve them.
Soil Pollutants
Soil pollutants in urban gardens can come from poorly managed industrial waste, sewage water, hydrocarbon emissions and wrong or excessive use of farm inputs like fertilizer and pesticides. The chemicals may become residues in the soil and reduce the fertility of the soil in the long term. Lead is the most prevalent contaminant in urban soils. However, in their paper on the environmental challenges facing the growth of urban agriculture , Wortman and Taylor indicate that plants grown on urban soils take up very little lead from the soil. However, the greatest threat comes from direct contact with the contaminated soil. The soil can be carried by farmers to their homes where little children can play with it and even put their contaminated hands in their mouths.
To combat the negative effects of soil pollution, all gardens should apply the guidelines on safe gardening provided by the US Environmental Protection Agency. Gardeners can minimize the amount of contaminants in their soil by constructing their gardens far away from railways and roads or by creating a hedge that will reduce contamination from poisonous gases blown by wind. Covering the soil with landscape fabric or mulch and using mulch to protect the garden beds from soil splash can also help to protect the soil from pollution. Gardeners can also use clean fill and topsoil obtained from certified sources or government approved extension programmes to protect the plants from pollution.
Water Shortage
Urban farmers find it difficult to locate reliable and safe sources of water for their gardens. Using water from the public water system can easily create shortages while overuse of ground or surface water can also reduce water supply for other city dwellers. In addition, the residues from pesticides and fertilizers on poorly managed urban gardens could cause chemical contamination of water sources and lead to the occurrence of waterborne diseases.
The major solution to water shortage is to use the existing sources of water judiciously and apply proven water conservation techniques. For instance, harvesting rain water can help to reduce pressure on the water from the public municipal water network. Gardeners can collect rainwater from roof tops and save them in plastic water tanks for use in the garden. In some cities, farmers use treated wastewater to irrigate their farms. Other low cost water conservation methods like drip irrigation can help also help farmers to make efficient use of water. Drip irrigation makes it possible to use low quality water sources like grey water that flows from the drains in most household kitchens.
Air Pollutants
Farmers in urban areas have to grapple with an increased amount of air pollution due the poisonous emissions from industrial chimneys, exhaust fumes from diesel and petrol engines, generators, and other machines. Changes in climatic conditions may also reduce the yield of crops grown by urban farmers. For instance, the higher atmospheric temperature in the cities may hinder the photosynthetic process in plants and affect their yield. Furthermore the higher concentration of certain gases including ozone can hamper the growth and yield of urban farm crops. A study was conducted in India on the effect of 6-hour mean concentration of ozone, nitrogen oxide and sulphuric oxide on biomass, pigment, physiological characteristics and yield on plants. The results of the study showed a significant reduction in these parameters on wheat, mung bean, palak and mustard.
The research into the effect of air pollution on plants is still ongoing and very few studies have been carried out to show how to reduce the effect of industrial air pollution on plants grown in urban gardens. However, one of the practical methods available is to plant ozone monitoring plants. The leaf surface of these plants can be used to monitor the effect of ozone gases on plants. Ozone causes unique symptoms on broad leaf plants which result in stippling or purpling on the leaf's upper surface. Very small spots will appear on the surface and these spots look droplets of finely ground chilly powder. Such symptoms help to detect excessive amounts of ozone in a particular neighbourhood.
Further research is still necessary to develop new ways to overcome the obstacles to urban agriculture and optimize the yield from these farms. Well managed urban gardens will help to reduce the cost of food and increase the profitability of the farms.
