Fertilizers and Environment

Citation:Saha, M.N., Ghorai, M.N., Jana, A.K. and Sen, H.S. (2010).Fertilizers as Non-point Source of Pollution and Management Options. Souvenir, Seminar on "Fertilizers and Environment", pp. 25-27, held at Calcutta University, Calcutta 26June 2010.

Fertilizers as Non-point Source of Pollution and Management Options

M.N.Saha1, Dipankar Ghorai2, A.K.Jana1 and H.S.Sen3

1Former Principal Scientist, 2SMS, KVK (Burdwan) and 3Former Director
Central Research Institute for Jute & Allied Fibres (ICAR), Barrackpore, WB 700 120

The world-wide per capita land base for agricultural production has declined dramatically over the past few decades and is expected to continue to decrease. For example, it is estimated that by the year 2025 the land in production per person will be 56 percent less than it was in 1965. The world population in 25 years is expected to be about 8 billion and hence 2 billion more than the current 6 billion. In India, it has crossed one billion mark and expected to reach 1.4 billion in the next 25 years. This trend will require that crop yields per unit of land continue to increase. These yield increases will in turn require greater nutrient inputs. It is also reasonable to assume that the impact of agriculture on the environment will be increasingly scrutinized since the public influence over production is growing. For harvesting 200 Mt of food grains every year, India is removing 25 Mt of plant nutrients from soil whereas the annual input from external sources such as fertilizers and manures is 33% less of the actual need. The scenario will be aggravated when the production target will be much more in coming years. This estimate is only for major nutrients, but the withdrawal and the demand for correcting the deficiency of micronutrients and secondary nutrients also suggest that the future could be sufficiently alarming in respect of these nutrients as well. While, short-supply of nutrients may be a generally observed phenomenon in Indian agriculture, its imbalanced and untimely application may certainly have detrimental consequences through pollution if not judiciously planned and applied.
Fertilizers and other agro-chemicals under intensive cultivation form non-point source of pollution in three ways, viz. groundwater contamination due to leaching, surface water contamination through runoff of excess nutrients or their derivatives, and altering the composition of atmospheric gases finally leading to warming of the climate.
Pollution due to major nutrients
Around 76% of the world's population lives in developing countries where more fertilizer-N is currently applied than in developed countries. Due to low N application rates during the last 5 or 6 decades, negative N balances in the soil were a characteristic feature of the crop production systems in developing countries. In future, with increasing fertilizer-N application rates, the possibility of nitrate pollution of groundwater in developing countries will be strongly linked with fertilizer-N use efficiency. A limited number of investigations from developing countries suggest that, in irrigated soils of Asia or in humid tropics of Africa, the potential exists for nitrate pollution of groundwater, especially if fertilizer-N is inefficiently managed. In developing countries located in the humid tropics, attempts have not been made to correlate fertilizer-N use with nitrate level in groundwater; however, fertilizers are being increasingly used. Besides high rainfall, irrigation is becoming increasingly available to farmers in the humid tropics and substantial leaching of N might also increase (Singh et al., 1995).
Non-point pollution caused by fertilizers and pesticides used in agriculture, often dispersed over large areas, is thus a great threat to fresh groundwater ecosystems. Intensive use of chemical fertilizers in farms and indiscriminate disposal of human and animal waste on land result in leaching of the residual nitrate causing high nitrate concentrations in groundwater. Nitrate concentration is above the permissible level of 45 ppm in 11 states in India, covering 95 districts and two blocks of Delhi. DDT, BHC, carbamate, endosulfan, etc. are the most common pesticides used in India. But, the vulnerability of groundwater to pesticide and fertilizer pollution is governed by soil texture, pattern of fertilizer and pesticide use, their degradation products, and total organic matter in the soil. Deposition of atmospheric nitrogen (from nitrogen oxides) also causes nutrient-type water pollution. In excess levels, nutrients over-stimulate the growth of aquatic plants and algae. Excessive growth of these types of organisms clogs our waterways and blocks light to deeper waters while the organisms are alive; when the organisms die, they use up dissolved oxygen as they decompose, causing oxygen-poor waters that support only diminished amounts of marine life. Nutrient pollution is a particular problem in estuaries and deltas, where the runoff that was aggregated by watersheds is finally dumped at the mouths of major rivers (Kumar and Shah, http://www.iwmi.cgiar.org/iwmi-tata/files/pdf/ground-pollute4_FULL_.pdf).

Similarly, pollution due to phosphates have also been reported. Excess and inappropriate application of P from either manure or commercial fertilizer can result in the eutrophication of fresh water bodies. The low-grade rock phosphate of Jhabua, Madhya Pradesh was investigated by Saxena and D’Souza ( 2005) for its possible application in the removal of lead, copper, zinc and cobalt ions from aqueous solutions. Effects of contact time, amount of adsorbent and initial concentration of metal ions were studied. Adsorption of heavy metal ions was found to follow the order: Pb2+ > Cu2+ > Zn2+ > Co2+. The probable mechanism of metal ion removal by rock phosphate was found to be by its dissolutions followed by subsequent precipitation.

Pollution due to arsenic and heavy metals
Everything points to arsenic being of natural origin although it is not yet possible to exclude the possibility that modern agricultural practices (groundwater abstraction from shallow wells, irrigation and fertilization) will have no influence on the groundwater arsenic concentrations. However, even normal amounts of arsenic are sufficient to give excessive arsenic in the groundwater if dissolved or desorbed in sufficient quantity. The British Geological Survey in their report in Bangladesh on 2001 further adds : Phosphorus enrichment parallels the distribution of arsenic enrichment (Anwar, 2004).
In a study on surface water conducted at 96 locations of the Ganga river in West Bengal (Kar et al., 2008) the dominance of various heavy metals followed the sequence: Fe > Mn > Ni > Cr > Pb > Zn > Cu > Cd for which indiscriminate use of fertilizers and pesticides, apart from unscientific disposal of industrial and domestic sewage, into the river system have also been held responsible. In another study (Begum et al., 2009) on Cauvery river water analysis of water, plankton, fish and sediment reveals that the Cauvery River water in the downstream is contaminated by certain heavy metals. Water samples have high carbonate hardness. Concentrations of all elements and ions increase in the downstream. Main ions are in the following order : Na >HCO3- >Mg > K > Ca> Cl > SO42-. Heavy metal concentration in water was Cr>Cu _ Mn > Co > Ni > Pb > Zn, in fish muscles, Cr > Mn > Cu > Ni > Co > Pb _Zn, in phytoplanktons, Co > Zn > Pb > Mn > Cr, and in the sediments, the heavy metal concentration was Co > Cr > Ni _ Cu > Mn > Zn > Pb. Although, the quality of Cauvery River may be classified as very good based on the salt and sodium for irrigation, Zn, Pb and Cr concentrations exceeded the upper limit of standards. They also concluded that metal concentrations in the downstream that increased the pollution load was due to the movement of fertilizers, agricultural ashes, industrial effluents and anthropogenic wastes.
Jayaraju et al. (2009) investigated the metal pollution documented in the skeletons of selected coral species like Acropora formosa, Montipora digitata and Porites andrewsi from the Tuticorin Coast, one of the least studied areas in the Bay of Bengal. Relating heavy metal concentrations to morphological features of skeletons, highest concentrations of all the metals (except Cu and Zn) were found in ramose or branching types of corals. Irrespective of their growth characteristics or patterns, all these species displayed higher concentrations of Pb, Ni, Mn and Cd within the skeletal part. The study area is currently exposed to a larger degree of metal pollution (natural and anthropogenic) than ever before as a result of the increasing environmental contamination from sewage discharges, the misuse of agricultural chemicals and fertilizers, and top soil erosion. The concentrations of heavy metals obtained in their study are compared with values from earlier works around the world. It indicates that corals are vulnerable to the accumulation of high concentrations of heavy metals in their skeletons and therefore can serve as proxies to monitor environmental pollution.

Climate pollution
Disproportionately high accumulation of toxic gases like methane, CO2 and NOx in the atmosphere has been observed world over, 28 % of which has been roughly estimated as due to agricultural practices. Among the various agricultural practices, 6 % was attributed to application of manures and fertilizers. Agricultural soils may act as significant carbon (C) sinks as well as sources. Increasing levels of soil organic C (SOC) can help mitigate the greenhouse effect by reducing atmospheric enrichment of carbon dioxide (CO2). Balanced fertility management as well as other management practices such as reduced tillage, can play a positive role in increasing C-sequestration from the atmosphere by crops and storage of C in soils. It has been suggested that organic cropping systems should eliminate emissions due to production and transportation of synthetic fertilizers. Components of organic agriculture could be implemented with other sustainable farming systems, viz., conservation tillage to further increase climate change mitigation potential. Improving fertilizer efficiency through practices like precision farming using GPS tracking can reduce nitrous oxide emissions. Other strategies include the use of cover crops and manures (both green and animal), N-fixing crop rotations, composting and compost teas, integrated pest management, etc. Fertilizer if and when applied through fertigation can minimize fertilizer loss and significantly increase fertilizer use efficiency.

Conclusions and policy inferences
Customized soil and crop specific fertilizer materials need to be developed for major cropping and farming systems in different agro-eco regions. Care should be taken to mitigate the deficiencies of nutrients for a cropping system as well as to limit the pollution caused by applied nutrients. Good fertility management should also result in reduced potential for soil erosion by producing a more healthy and vigorous crop that closes the canopy and covers the soil more rapidly. More biomass is produced with adequate and balanced fertilization.
Preventive and curative measures against pollution and contamination of groundwater may continue to receive low priority for years to come, and technological measures to prevent the ill- effects on human health will get priority in short term. Demineralization using Reverse Osmosis (RO) system can remove all hazardous impurities from drinking water and would be cost effective in many situations where TDS, nitrate and fluoride in groundwater are above permissible levels. The cost of demineralization is falling rapidly. Saudi Arabia meets 20 per cent of its total water needs from desalinated sea water and Saudi technologists believe desalination costs would fall so rapidly over the coming decades that desalination will be cheaper than pumping coastal aquifers. Low cost treatment methods are available for removal of arsenic from groundwater. There are, however, challenges that water utilities would face such as building technical and managerial skills to design, install, operate and manage water treatment systems, making people pay for treated water and building knowledge and awareness among communities about groundwater quality issues and treatment measures. For the long run, policies need to be focused on building scientific capabilities of line agencies concerned with Water Quality Monitoring (WQM), water supplies, and pollution control; and restructuring them to perform WQM and enforcement of pollution control norms effectively and to enable them implement environmental management projects (Kumar and Shah, http://www.iwmi.cgiar.org/iwmi-tata/files/pdf/ground-pollute4_FULL_.pdf). The Government of India is in the process of revising its existing regulatory limits related to metal contents in organic fertilizers due to pressures from different stakeholder groups. The study conducted by Saha et al. (2009) has generated information on maximum permissible loading limits for two important metals, Pb and Cd, which can prevent contamination of food chain in almost all the situations of soil and crop conditions of the country. Hence, these limiting values can be considered as the basis for formulating different regulatory laws and orders for the purpose of restricting the activities related to metal entry into soil, like limits related to maximum permissible concentrations in fertilizers, manures, amendment materials; environmental impact assessment prior to initiating industrial activities, giving permission for setting up special economic zone, etc., are to be framed on such basis.
Mudgal et al. (2010) suggested ‘green’ technology, in other words phytoremediation, to introduce plants tolerant to heavy metal contamination for which mechanism of tolerance of heavy metal at physiological and genetic level is essential.

References
Anwar J. (2004). Arsenic and uranium in fertilizer (http://www.sos-arsenic.net/english/tsp.html).
Begum, A., Ramaiah, M., Harikrishna, Khan, I. and Veena, K. (2009). Heavy metal pollution and chemical profile of Cauvery river water. E-Journal of Chemistry 6(1): 47-52 (http://www.e-journals.net 2009).

Jayaraju, N., Sundara, B.C., Reddy, R. and Reddy, K.R. (2009). Heavy metal pollution in reef corals of Tuticorin coast, southeast coast of India. Soil and Sediment Contamination : An International Journal 18(4): 445-454.
Kar, D., Sur, P., Mandal, S.K., Saha, T. and Kole, R.K. (2008). Assessment of heavy metal pollution in surface water. International Journal of Science & Environmental Technology 5(1): 119-124.

Kumar, M. D. and Shah, T.. Groundwater pollution and contamination in India: The emerging challenge (http://www.iwmi.cgiar.org/iwmi-tata/files/pdf/ground-pollute4_FULL_.pdf).

Mudgal, V., Madaan, N. and Mudgal, A. (2010). Heavy metals in plants: phytoremediation : Plants used to remediate heavy metal pollution. Agriculture and Biology Journal of North America. (Science Huβ, http://www.scihub.org/abjna).
Saha, J.K., Panwar, N.R. and Singh, M.V. (2009). Determination of lead and cadmium concentration limits in agricultural soil and municipal solid waste compost through an approach of zero tolerance to food contamination. Environmental Monitoring Assessment (DOI 10.1007/s10661-009-1122-3).
Saxena, S. and D'Souza, S.F. (2005). Heavy metal pollution abatement using rock phosphate mineral (doi:10.1016/j.envint.2005.08.011).

Singh, B., Singh, Y. and Sekhon, G.S. (1995). Fertilizer-N use efficiency and nitrate pollution of groundwater in developing countries (doi:10.1016/0169-7722(95)00067-4).