Abstract
Tea production in the Kenyan Rift Valley uses high rates of nitrogenous fertilizer. Nitrates can be discharged to water bodies through leaching and surface run‐off. Nitrate levels above 10 mg/L –N cause methemoglobinemia which is fatal. A study to monitor changes in surface water nitrate levels was carried out in ten rivers within a Kenyan tea plantation for three years. Water samples were obtained before and after fertilizer application in 2004, 2005, and 2006. Nitrate‐nitrogen (–N) was determined colorimetrically by the cadmium reduction method using HACH‐DR 2400 dataloging spectrophotometer. For the three years, the highest nitrate‐nitrogen levels were in river Temochewa in 2005 during the first fertilizer applications (4.9 mg/L to 8.2 mg/L). There was no established trend between surface water nitrate levels and the time of fertilizer applications; however, fertilizer application contributed to an increase in nitrate levels. The initial nitrate‐nitrogen levels in most of the rivers were high, indicating that contamination could have been upstream; hence, further research is required to establish this. Nitrogen‐nitrogen levels in the three years were below the maximum contaminant level of 10 mg/L –N; however, the rivers should be monitored frequently.
Highlights
Tea production is the main agricultural activity practiced in the Kenyan highlands and Ri valley. e optimum production of a mature tea eld is 3,500 kg made tea per hectare per year [1]; to sustain the yields, soil nutrients are replenished by the use of inorganic compound fertilizers
Sheep, baby pigs, chicks, and horses are susceptible to nitrate poisoning [14]. e oxidation of nitrite to nitrate by dissolved oxygen in water leads to depletion of the oxygen level in water [15]. e US Environmental Protection Agency (USEPA) and National Environmental Authority in Kenya (NEMA) xed a MCL of 10 mg/L, NO3–N [16, 17]
The effect of fertilizer application on surface water nitrate levels was investigated. ere was an effect of runoff observed in 2006 a er the rst application as the nitrate levels increased
Summary
Tea production is the main agricultural activity practiced in the Kenyan highlands and Ri valley. e optimum production of a mature tea eld is 3,500 kg made tea per hectare per year [1]; to sustain the yields, soil nutrients are replenished by the use of inorganic compound fertilizers. In Nandi South district, fertilizer application is carried out during rainy seasons in May and October; surface runoff and leachate get into rivers passing through the tea plantations which could cause river eutrophication and nitrate pollution. Land use, fertilizer pattern, fertilizer usage, soil type, rainfall pattern, irrigation, climatic conditions, and depth of ground water below land surface are the main factors that control the leaching of nitrates as well as nitrites [9]. Consumption of drinking water contaminated with high levels of nitrates by infants below six months old and certain young animals causes “oxygen debt” in the blood, a fatal condition known as methemoglobinemia or blue baby syndrome [10,11,12,13]. Sheep, baby pigs, chicks, and horses are susceptible to nitrate poisoning [14]. e oxidation of nitrite to nitrate by dissolved oxygen in water leads to depletion of the oxygen level in water [15]. e US Environmental Protection Agency (USEPA) and National Environmental Authority in Kenya (NEMA) xed a MCL of 10 mg/L, NO3–N [16, 17]
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