Controlling the Soil, Water and Air Pollution due to Fertilizers by Increasing Their Nutrients Use Efficiency through Slow Release Technology Fertilizers contain nutrients added to the soil in organic or synthetic from, that most commonly include phosphorus, nitrogen and/or potassium (EPA 2007). Between 1960 and 1995, global fertilizer use for nitrogen increased by seven times its previous amount. However, only 30-50% of this amount is actually taken up by plants allowing much of it to be washed away from fields into the surrounding ecosystem. This can lead to over-enrichment of the surrounding ecosystem and eutrophication. Using organic fertilizers tends to reduce the risk of runoff by slowly releasing nutrients into the surrounding crops (Tilman 2007). Urea is the predominant form of N fertilizer worldwide (>50%) (IFA 2011) and also in Pakistan (ca. 70%), principally because of its lower cost per unit of N, and the convenience for transport, storage and spreading, attributes which result from its higher N content (46% N), in comparison to the 35, 26, 21, and 18% N of ammonium nitrate (AN), calcium ammonium nitrate (CAN), ammonium sulphate (AS) and di-ammonium phosphate (DAP), respectively. However, urea has been reported to have lower N response efficiency (NRE), where NRE is defined as kg of additional dry matter (biomass and grain) produced per kg of applied N, when compared to other ammonium- and nitrate-based fertilizers. This is especially so if urea is applied under non-optimum soil moisture (very dry) and high temperature (above 20oC) conditions. The lower NRE of urea has always been attributed to the wide range of N losses (5% to 53% of the applied N) as ammonia (NH3), when compared to AN, CAN, AS and DAP (Zaman et al., 2008; Saggar et al., 2012). Of course, some N losses, like gaseous emissions of NH3, nitric oxide (NO), nitrous oxide (N2O) and molecular N (N2) and immobilization by microorganisms to organic N, will be unavoidable because they are part of the natural N cycle and would occur after application of any ammonium-based fertilizer or dairy farm effluents. Hence, controlling the rate of all of these N losses is critical for improving the response efficiency of all chemical fertilizers and controlling the emission of greenhouse gases (GHGs) and NO3 leaching. Most studies (Schwab and Murdock., 2005) indicate that nitrogen losses can be reduced in these situations when a urease inhibitor is applied to the fertilizer. Urease inhibitors prevent the urease enzyme from breaking down the urea. This increases the probability that urea will be absorbed into the soil after a rain event rather than volatilized into the atmosphere. This causes subsequent hydrolyzation to occur below the soil surface and decreases atmospheric losses. The use of inhibitors also decreases the localized zones of high pH common with untreated urea (Watson et al., 2008) During the past decade, researchers have developed a variety of management practices and technologies to improve the NRE of urea. One such approach is to treat granular urea with the urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT - trade-name Agrotain®). The nBTPT is typically applied at a range of 250 to 500 mg per kg of urea in order to delay urea’s hydrolysis by 7 to 10 days (Zaman et al., 2008). Similarly, urea can also be treated with both nBTPT and nitrification inhibitors like dicyandiamide (DCD) or 3, 4-dimethylpyrazol-phosphate (DMPP) have gained commercial adoption in agricultural system. Treating urea with both urease and nitrification inhibitors has the dual benefit of delaying urea hydrolysis while also retaining N in a less mobile form like NH4+, which in turn can reduce N2O emission and NO3- leaching under a range of cropping conditions (Dobbie and Smith, 2003; Zaman et al., 2008, 2010; Soares, et al., 2012; Zaman and Nguyen, 2012). After application, DMPP is less prone to leaching and remains effective much longer than that of DCD. Similarly, fertilizer use efficiency can be further improved if urea is applied with different additives like plant growth hormones or regulators. The word ‘hormone’ came from Greek language, where it means ‘to stimulate’ or ‘to set in motion’. Plant hormones/growth regulators (PGR) are a group of naturally occurring organic substances, which have the ability to influence physiological processes such as plant growth, differentiation and development, stress responses, cell division and reproductive activities when applied at a very low concentrations. Among the major classes of PGRs, auxins (generally represented by indole-3-acetic acid (IAA)), the gibberellins (GAs), and the cytokinins (CKs) have the most potential to be used as plant growth regulators. The combination of above mentioned few or all substances and practices can increase the nutrients use efficiency from fertilizer and reduce the environmental impact. References EPA.“Nutrient Management and Fertilizer. Agriculture.epa.gov/agriculture/tfer.html (accessed 18 December 2007). Tilman, David et al. “Agricultural Sustainability and Intensive Production Practices.” Nature 418 (2002): 671-677 Saggar, M., King, B., Zanesco, A., MacLean, K., Aichele, S., Jacobs, T. L., et al. (2012). Intensive training induces longitudinal changes in meditation state-related EEG Zaman, M. Nguyen, M.L. & Saggar, S. (2008c). N2O and N2 emissions from pasture and wetland soils with and without amendments of nitrate, lime and zeolite under laboratory condition. Australian Journal of Soil Research, 46, pp. 526-534. Schwab, G.J. and Murdock, L.W. (2010): Enhanced-Efficiency Nitrogen Fertilizer for Corn and Wheat Production. IFA International Conference on Enhanced-Efficiency Fertilizers, Miami, International Fertilizer Industry Association, Paris, France. Watson, C.J., et al. "Rate and mode of application of the urease inhibitor N-(n-butyl) thiophosphoric triamide on ammonia volatilization from surface-applied urea." Soil Use and Management, British Society of Soil Science (2008): 1-7. Soares JR, Cantarella H, Menegale MLC. Ammonia volatilization losses of surface-applied urea with urease and nitrification inhibitors. Soil Biol Biochem 2012; 52:82–9. Zaman, M. & Nguyen, M.L. (2010). Effect of lime or zeolite on N2O and N2 emissions from a pastoral soil treated with urine or nitrate-N fertiliser under field conditions. Agriculture Ecosystems and Environment, 136, pp. 254-261.
Posted on: Tue, 27 Aug 2013 06:52:02 +0000
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