Fate of urea fertilizers in sandy aquifers: laboratory and field case study from Kalpitiya, Sri Lanka

Abstract

Abstract:High nitrate (NO 3 -) levels in groundwater are attributed to fertilizer leaching from sandy soil. A simulation laboratory study was performed to investigate the fate of leached urea in an agricultural field in Kalpitiya and the enhancement of fertilizer retention in sandy soil. A field experiment was conducted to investigate the effectiveness of using nutrient rich groundwater to reduce the nitrate levels in the Kalpitiya aquifer. Nitrate retention experiment revealed that increasing clay up to 15 % increased the retention by > 50 % with an efficiency of 3.7 % and the retention is conversely correlated with the quantity of clay. A soil column experiment showed that nitrate concentration of leachate increases rapidly for an initial period of 250 hours and then started to decrease gradually. Initial nitrification followed by denitrification reactions may be the causative factors for this behaviour. The study further revealed that clay and organic manure are potential sinks of nitrate while the latter is also a source of nitrate. Gradual building up of nitrate in the groundwater of the aquifer system appears to be due to available favourable conditions for continuous nitrification while cycling through the aquifer due to intensive irrigation. This field case study reveals that a polluted aquifer can probably be recovered by reusing the nitrate contaminated groundwater as a source of fertilizer for the crops cultivated on the land above the aquifer allowing longer contact time for plant uptake. The process can gradually purify the groundwater while allowing farmers to use less nitrate fertilizers.

Assessment of hydrogeological scenario in a cross-section from Anamaduwa to Kalpitiya in Northwest Sri Lanka

“…People of both areas tend to extract groundwater on a large scale by constructing dug and tube wells into subsurface unconsolidated sandy and deep sedimentary limestone aquifers. The excessive groundwater usage has caused several detrimental environmental impacts, such as the depletion of groundwater table due to unregulated pumping (Water Resources Board, 2010) and deterioration of water quality due to saltwater intrusion and agrochemical usage (Kuruppuarachchi and Fernando, 1999;National Water Supply and Drainage Board, 2008;Jayasingha et al, 2011;Jayasingha et al, 2013;Jayasingha et al, 2014;Kumarasinghe and Rajapakse, 2013;Jayathunga et al, 2020). To cater solutions to the aforementioned issues, a general understanding of the physical regime and groundwater dynamics are necessary, which would depend on geology, land use, climate, and other environmental factors of the respective areas.…”

In vitro selection of chili (Capsicum annum) varieties tolerant to declined nitrogen supplements

“…However, due to the soils lacking positively charged sites for adsorbing negatively charged nitrate nitrogen (NO 3 − irons), they are extensively leached-down being the main mode of loss specially from the sandy soils (Xiong-Hui et al 2011). The problem gets worsen in the areas with hot/arid climate with higher temperature levels where the higher decomposition rate limits the available organic matter contents to the very low level as reported in the Kalpitiya area in Sri Lanka, where the sandy regosols is the predominant soil type (Jayasingha et al 2013). Thus, farmers often tend to apply excessive amounts of nitrogen fertilizers, while further increments are applied during rainy season to compensate the losses due to leaching (Jayasingha et al 2013).…”

“…The problem gets worsen in the areas with hot/arid climate with higher temperature levels where the higher decomposition rate limits the available organic matter contents to the very low level as reported in the Kalpitiya area in Sri Lanka, where the sandy regosols is the predominant soil type (Jayasingha et al 2013). Thus, farmers often tend to apply excessive amounts of nitrogen fertilizers, while further increments are applied during rainy season to compensate the losses due to leaching (Jayasingha et al 2013). Furthermore, if the area prevails higher temperature levels, the problem is severe since heavy irrigation is demanded to cool-down the environment.…”

Farmer Perception, Environmental Awareness, and Overuse of Fertilizer in Kalpitiya: A Preliminary Investigation using Bayesian Econometrics

“…Most farmers who overuse chemicals believe that those chemicals in the market are of low quality (Fasina, 2013). Despite best management practices recommended by the research institutions, indiscriminate use of chemical fertilizers and low use efficiencies of fertilizers under tropical conditions, have increased environmental pollution, negatively affecting human and ecosystem health, and creating social and political unrest in the country (Jayasingha, et al, 2013). Agronomic practices adopted by farmers further degrade soil fertility threatening the food security in Sri Lanka.…”

“…Farmers often tend to apply excessive amounts of nitrogen fertilizers, while further increments are applied during the rainy season to compensate for losses due to leaching (Jayasingha et al, 2013). The retention of Nitrogen (N), which is essential for plant growth, is influenced by a variety of factors including soil constituents, irrigation practices and the fertilizer application in terms of type and the quantity (Rinaudo et al, 2005).…”