Measures to Mitigate Adverse Effect of Excess Use of Nitrogen Fertilizer on Environment

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Excess nitrogen will pollute the water as well as air. Nitrogen at higher levels causes a loss of entire plants, depletion of soil nutrients, death of fish and aquatic organisms and contamination of ground water. Different management options can be followed to supply adequate amount of nitrogenous fertilizer to the crop for optimum production and minimal losses into the environment.  Increase the use efficiency of nitrogen is the alternate way to reduce the adverse effect of nitrogen fertilizer on environment. Since fertilizer nitrogen is mostly lost either through leaching or denitrification after its conversion to nitrate, use of specific chemicals inhibits the conversion of ammonium to nitrate was considered as appropriate method to reduce the loss of nitrogen from the field. The most widely used urease inhibitor are  NBPT [N-(n-butyl) thiophosphorictriamide]  which will reduce NH3 volatilization losses due to urea application there by increasing the loss of nitrogen to the environment and increasing the nitrogen use efficiency and nitrification inhibitors are N serve or Nitrapyrin which will reduce the denitrification process there by increasing the nitrogen use efficiency in crop.

Many times low N-use efficiency in crops is observed due to lack of synchronization between crop demand and release of N from water-soluble sources like urea. Application of soluble N fertilizers in split doses is an attempt to increase the degree of synchronization between supply and demand of N, but there is a limit to achieve it. In recent decades, controlled-release N fertilizers have been developed that consist of highly soluble urea prills or granules coated with water- insoluble materials like sulphur or polyolein that control the rate, pattern, and duration of N release (Shaviv 2001). Besides the advantages of controlled-released fertilizers in reducing N losses to the environment and increasing fertilizer N-use efficiency (Chalk et al. 2015; Pandey and Singh 1987; Patil et al. 2010; Wang et al. 2015; Yan et al. 2008; Ye et al. 2013), the rate of nitrogen fertilizer application and the number of applications during the growing season can often be reduced, which has the added advantage of saving labor costs. In recent years, different variants of polymer coated controlled release urea have been designed to synchronize N release and crop N uptake with minimal leakage of N to the environment. These have already been tested for obtaining high yields of rice along with high N-use efficiency (Kondo et al. 2005; Patil et al. 2010; Singh et al. 2007; Wang et al. 2015; Yan et al. 2008; Ye et al. 2013; Zhang et al. 2012). The commonly used slow releasing nitrogenous fertilizer are Neem coated urea, sulphur coated urea, prilled and tar coated urea will also increase NUE by releasing the nitrogen slowly to the plant there by reduce the nitrogen lost through leaching and run off.

The rate, source, time of application, and method or placement of N fertilizer also determine N recovery efficiency. Applying quantity of fertilizer N calculated by considering soil N supply rather than following traditional farming practices resulted in an increase in N-use efficiency by 40–50 %, Thereby minimizing the loss of nitrogenous fertilizer to the environment. Use of chlorophyll meters, leaf color charts (LCC), optical sensors, ground-based remote sensors, and digital, aerial, and satellite imageries also increase the nitrogen use efficiency by quantifying the need of nitrogen  fertilizer requirement by the crop there by reducing excess application of nitrogenous fertilizer and reduce the loss of nitrogen to the environment through volatilization, leaching and run off.

Using breeding and genetic engineering techniques scientist identified the two genes that control nitrogen consumption: one that codes for DELLA proteins, and another that codes for a protein called growth-regulating factor 4 (GRF4), which had been thought to increase only grain size and yield and it found that GRF4 counteracts the effects of DELLA proteins by encouraging plants to absorb and metabolize nitrogen and carbon to support growth. Then the researchers breed rice plants to produce a higher concentration of the GRF4 protein. The result was short, plants with high yields that required less nitrogen than conventional green-revolution varieties. These varieties require less fertilizer and nitrogen absorption per cent is more compared to earlier varieties led to reduction in GHG (Green House Gas- CH4 &N2O) emission.

Increasing the nitrogen use efficiency by adopting improved Nitrogen management practices like use of slow releasing fertilizer, urease and nitrate inhibitors, Leaf colour chart, chlorophyll meter, soil test based N application is an alternative methods to reduce the nitrogenous fertilizer loss through leaching, volatilization, and run off thereby we can mitigate adverse effect of nitrogenous fertilizer on environment.

Author: Vanitha T K- JRF(P), Bioengineering and Environmental Sciences Lab, CEEFF, CSIR-IICT, India.

Image Source: Witt C, Pasuquin JMCA, Mutters R, Buresh RJ. 2005. New leaf color chart for effective nitrogen management in rice. Better Crops 89 (no. 1):36–39.


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