Wheat, rice and corn are among staple food crops of Pakistan, producing 24 million tons (MT) of wheat, 5.54 MT of rice and 3 MT of corn in 2013. The production of these crops was observed to be less than half in 1990s. The significant increase in crop yield compared to last two decades is due to the intensive use of inorganic fertilizers and other improved management practices. Wheat, rice and corn, which feed the major population of the world, are nitrogen-hungry crops. These crops require nitrogen other than provided by the nature. More than 90 per cent of the farmers in Pakistan are adapted to the inorganic fertilizers to enhance their crop production. The trend towards the use of organic fertilizers (Farm manure, bio-fertilizer, green manure, etc.) is quite low in Pakistan.
The introduction of high yielding varieties to meet the food requirements of the ever-increasing population has resulted in increased use of fertilizer to satisfy the nutrient requirements of these high yielding varieties. The lower prices of the crops at the time of harvest and high fuel and electricity prices have pushed the farmers to enhance production using fertilizers to justify the cost related to input at the expense of environmental contamination.
More than a hundred million tons of nitrogen fertilizer is applied worldwide every year, with more than half in developing countries like Pakistan. Pakistans soil simply could not provide enough food to 180 million of population without the use of nitrogen fertilizers. The increase in the Pakistans population would not only be the reason to enhance the agricultural production, but it should be done in a sustainable fashion, not at the expense of environmental damage. The green revolution has pushed the agriculture sector to improved management practices including fertilizers, pesticides, herbicides and other inputs. The intensive use of these agrochemicals has not only polluted the soil, water and air but also affected the human beings. Our fear of hunger has pushed the farmers to grow staple crops with maximum calories, but these staple crops tend to use nutrients in excess from the soil. Depleted soil nutrients result in lower crop yield, leaving farmers financially strapped to afford fertilizer, from whatever source. As a result, most of the commercial fertilizers are imported and results in increased cost of production. The intensive use of nitrogen based fertilizers has pronounced effects on our environment.
Intensive use of inorganic fertilizers has paved the way for deterioration of soil health, leaving the effects of illness on plants, human being and animals. The losses of nitrogen to the environment are in the form of subsurface leaching, volatilization and nutrient runoff towards the water bodies. About 40-60 per cent of applied nitrogen is lost through volatilization, de-nitrification and subsurface leaching, eventually contaminating the environment. Excessive use of fertilizers can cause the acidity or alkalinity of the soil which can have an impact on crop yield due to imbalance of nutrients availability and affects the microbial activities in the root zone. Excess use of urea in rice production system enhances the growth of bacteria, causing a human disease. Nitrosamine illness is caused by the presence of secondary amines which causes cancer in human beings. Nitrates, vapours of amonia and nitrate aerosols cause respiratory illness.
Agricultural system is not only the sources of the environmental pollution but other combustion activities (cars and electric generators) are also responsible for the release of nitrogen oxides into the atmosphere. One of our goals has been to maintain a sustainable closed system. Inorganic fertilizers when applied using proper rates in conjunction with suitable timing can promote the crop growth and yield. However, the excessive use of fertilizers can have serious impact on the environment.
Management strategies to reduce soil nitrogen losses for sustainable agriculture include proper timing of applications, split fertilization, development of procedures to determine in season nitrogen availability and manure recommendations instead of nitrogen fertilization. Replacing the traditional methods with variable rate fertilizer applications, adoption of nutrient management planning, application of urea inhibitors, and use of nitrogen fertilizer sources that are suitable for local environmental conditions can reduce nitrogen losses.
Better assessments of local weather forecast combined with predictive modeling approach can provide timely information to growers and agricultural professionals to make up to date recommendations on nitrogen fertilizer use assuring the long-term fertility of soils through management of soil organic matter, microbial activity and careful mechanical interference.
Nitrogen fixation via legumes and biological activity, effective recycling of organic materials, crop rotations to control weed and disease, insect control, farm yard manuring and resistant varieties could be the alternative ways to protect environment from fertilizer sources. Plant breeders should also come up with the breads/varieties requiring lower amounts of nitrogen based inorganic fertilizers to reduce nitrogen losses to the environment.
The author is associated with the Institute of Soil and Environmental Sciences, University of Agriculture Faisalabad.