International Journal of Applied Earth Observation and Geoinformation 12 (2010) 190–200 Contents lists available at ScienceDirect International Journal of Applied Earth Observation and Geoinformation journal homepage: www.elsevier.com/locate/jag Non-point source pollution in Indian agriculture: Estimation of nitrogen losses from rice crop using remote sensing and GIS Abha Chhabra ∗ , K.R. Manjunath, Sushma Panigrahy Agriculture Forestry and Environment Group, Remote Sensing Applications Area, Space Applications Centre, Indian Space Research Organization, Ahmedabad 380015, Gujarat, India article info Article history: Received 6 October 2009 Accepted 12 February 2010 Keywords: Nitrogenous fertilizers Rice crop Leaching loss Ammonia volatilization loss Indo-Gangetic plain region abstract The paper presents a detailed understanding of nitrogenous fertilizer use in Indian agriculture and esti- mation of seasonal nitrogen loosses from rice crop in Indo-Gangetic plain region, the ‘food bowl’ of the Indian sub-continent. An integrated methodology was developed for quantification of different forms of nitrogen losses from rice crop using remote sensing derived inputs, field data of fertilizer application, collateral data of soil and rainfall and nitrogen loss coefficients derived from published nitrogen dynam- ics studies. The spatial patterns of nitrogen losses in autumn or ‘kharif’ and spring or ‘rabi’ season rice at 1 × 1 km grid were generated using image processing and GIS. The nitrogen losses through leaching in form of urea-N, ammonium-N (NH 4 -N) and nitrate-N (NO 3 -N) are dominant over ammonia volatilization loss. The study results indicate that nitrogen loss through leaching in kharif and rabi rice is of the order of 34.9% and 39.8% of the applied nitrogenous fertilizer in the Indo-Gangetic plain region. This study provides a significant insight to the role of nitrogenous fertilizer as a major non-point source pollutant from agriculture. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Agriculture has been identified as the largest contributor of non-point source (NPS) pollution of surface and ground water sys- tems globally (Thorburn et al., 2003). Fertilizers, which are used as important inputs in agriculture to supply essential nutrients like nitrogen (N), phosphorus (P), and potassium (K) also serve as a major non-point source pollutant. They undergo transformation through various physical, chemical, and biological processes in soil. From the beginning of green revolution, nitrogen fertilizer use has been a success story for Indian crop production. The increase in nitrogenous fertilizer application in the last four decades (0.05 Mt in 1950–1951 to 11.7 Mt in 2004–2005) has resulted in unprece- dented increase in agricultural production in the northwestern India leading to food security of the country (NAAS, 2005). Recently, concerns have been raised regarding consequences of fertilizer use more particularly nitrogenous fertilizers, since fertilizer recovery efficiency of nitrogen seldom exceeds 50% and a major portion of applied fertilizer is lost from plant–soil system by various soil processes. Therefore, the losses of reactive nitrogen from agricul- tural systems are a serious cause of concern for both economic and environmental reasons (Raghuram et al., 2007). Assessing the envi- ronmental impacts of non-point source pollutants at a localized ∗ Corresponding author. Tel.: +91 79 2691 4007; fax: +91 79 2691 5823. E-mail address: abha@sac.isro.gov.in (A. Chhabra). and regional scale is of prime importance to achieve sustainable agriculture. Rice is the most dominant food crop of India. Nitrogen is the sin- gle most important nutrient element that has a profound effect on the growth and yield of rice. Most of the Indian soils are deficient in available N, and rice crop invariably respond to the application of fertilizer-N in almost all the Indian soils (Panda et al., 2007). Among the different forms of fertilizer nitrogen, nitrate (NO 3 - ) is highly mobile and most susceptible to leaching, ammonium (NH 4 + ) the least and urea-N is moderately susceptible. Urea is the most common form of nitrogenous fertilizer applied to rice crop in India. When urea is applied to aerobic or flooded rice soil, it hydrolyses to ammonium carbonate by the enzyme urease, principally produced by soil microbes. Depending upon the alkalinity and pH buffering capacity of soil, ammonium carbonate decomposes and ammonia gas escapes to the atmosphere resulting in ammonia volatilization loss. Urea hydrolysis is maximum in soils with high organic car- bon or added organic manure or green manure, pH around 8.0, moisture status at field capacity, and temperature around 35 ◦ C (Panda et al., 2007). The ammonium ion resulting from urea hydrol- ysis also undergoes biochemical oxidation (nitrification) in aerobic soil as well as at three sites in submerged rice soil system viz. top oxidized soil layer, rice rhizosphere, and flood water. The diffu- sion of nitrate into the anaerobic zone in the submerged soil also results to denitrification loss (N 2 O, N 2 ) of nitrate (NO 3 - ) formed. Nitrate leaching is dominant when both soil nitrate content and water movement are high. The NO 3 - anion is very soluble in water, 0303-2434/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jag.2010.02.007