Soil can be defined as a mixture of mineral and organic matter that is capable of supporting plant life. Agriculture is a major occupation in countries such as India and Ireland and the quality of agricultural productivity depends upon the quality of soil. With increasing population, use of fertilizers has been widely practiced over the past century to meet the higher food demand. Nitrogen is the only nutrient which is less available for plants and because of this most fertilizer inputs are in the form of nitrogen. Since the major input of fertilizers is in the form of nitrogen, this article will be focusing on its usage and impacts upon soil and environmental quality.
Nitrogen as a fertilizer – why?
It is a known fact that nitrogen constitutes about 78 % in the atmosphere and is required by all organisms (Galloway, 1998). Nitrogen is the nutrient most often applied in the form of a fertilizer because plants require large amounts of nitrogen for growth, but usually a very small proportion is naturally available to them (Tan, 2000).
Although chemical fertilizers are widely used, farmers are not always aware of their consequences.
So what are the consequences?
- Soil Quality – it affects the soil nutrient levels, microbial community and hence the soil fertility and quality. Fertilizer use has been found to affect the carbon pools in soil, thus causing an imbalance in the soil nutrients.
- Cost – it’s expensive for farmers.
- Contaminates groundwater – Environmental impacts due to the release of NOx (Nitrous oxide and Nitric oxide) emission or leaching in soil which has a potential to contaminate the groundwater. The extent of leaching depends on the soil type. For example, there has been evidence that leaching is less in clay soils as compared to sandy soils. (This must be noted while performing fertilizer application).
- Contaminates our air – Nitrous oxide (NO2) is a harmful greenhouse gas and hence it is important to control its release from the soil. Nitrogen fertilization influences the natural growth pattern of crops such as barley, tomato and more.
- Affects plant growth – If the soil nutrient levels are altered, the normal growth pattern of plants or crops have been found to be restricted. Use of fertilizers not only affects the soil organic matter concentration, but also becomes expensive for farmers to apply on their fields.
- Soil pollution – Research by Atafar et al. (2010) suggested that fertilizer application leads to elevated concentration of heavy metal in the soil such as lead, arsenic and cadmium. The lead and arsenic levels tend to increase more rapidly as compared to those of cadmium. Taylor and Percieval (2001) investigated that heavy metals accumulated in the soil eventually pass on to plants and then animals via the food chain (Atafar et al., 2010). This means that such a produce when consumed by humans, is not of the highest quality.
For the various reasons explained above, reducing the application of chemical fertilizers has been discovered to be more beneficial for the quality of the yield and the environment.
What can be done instead of using fertilizers?
Studies conducted by the author of this article suggests planting mixed species containing legumes (such as white clover or Trifolium repens) naturally increases the soil nitrogen levels which enables to reduce nitrogen fertilizer inputs. Evidence from other research works suggests that to avoid NOx emissions, incorporating leguminous species such as clovers into agricultural practices can be established.
What are legumes?
Legumes are plants that bare their fruit in pods – common examples include beans, peas and lentils.
Legumes have the ability to fix atmospheric nitrogen due to the presence of symbiotic bacteria in their root nodules. When legumes (such as white clover or Trofolium repens) are incorporated into agricultural plots, less nitrogen inputs as fertilizers is required thereby making the farming sustainable. Moreover, it has been found that the presence of legumes, results in a higher yield.
This is one potential solution towards reducing nitrogen fertilizer inputs which would in turn; reduce the various consequences caused by its application.
About the Author:
Antara Chakrabarti, currently based in Dublin has completed her Masters’ in Applied Environmental Science. Her primary area of research interest revolves around Ecology and matters related to it such as nutrient levels, conservation and urban farming. In her spare time, she pursues hobbies such as: reading, writing, traveling, knitting, and playing badminton. She also enjoys spiritual practices, mind training and helping people in whatever way she can.
Atafar, Z, Mesdaghinia, AlirezaNouri, J, Homaee, M, Yunesian, M, Ahmadimoghaddam, M & Mahvi, A.H. (2010). Effect of fertilizer application on soil heavy metal concentration. Environmental monitoring and assessment, 160: 83-90.
Galloway, James N (1998). The global nitrogen cycle: changes and consequences. Environmental Pollution, 102: 15-24.
Chakrabarti, A. (2014). Effect of sward mixture on Total Oxidised Nitrogen (TON) in soil solution. MSc Applied Environmental Science Thesis. University College Dublin.
Tan H.K (2000). Environmental Soil Science 2nd edition, revised and expanded. Chapters 1-8.
Troeh R.F and Thompson M.L (1993). Soils and Soil Fertility. Oxford University Press.