Abstract :

Phosphorous (P) is an essential element to plant growth and development necessitating P fertilizer applications for agricultural crops for better yields.  Paddy, the main food crop of Sri Lankans is a fertilizer intensive crop where phosphorus nutrition is achieved via triple super phosphate applications. Since water circulating system of paddy fields are connected to other water bodies this soluble P can contaminate the nearby waterbodies. To detect the extent of P fertilizer leaching from paddy fields, a lysimeter experiment was carried out in the Low Country Intermediate zone, Sri Lanka for four consecutive growing seasons from 2015 to 2016. Paddy fields under two management practices; control run-off and continual run-off conditions were selected for the study. The farmers practice the Department of Agriculture recommended fertilizer application schedules. Lysimeters were placed in a Randomized Complete Block Design with triplicates at  upper and lower ends of the gradient of the each site. Water samples were collected below the root zone, at a depth of 30 cm, irrigated, run-off, nearby water reservoirs and analyzed for water soluble of phosphate. The highest concentration of total phosphate in leached water (0.88 mg/L) did not exceed the drinking water standard threshold level of 2 mg/L of Phosphate. The quantified leached total Phosphate amount for controlled run-off condition and continual run-off condition were 0.49 ± 0.10 kg/ha and 0.46 ± 0.04 kg/ha, respectively without statistically significant differences. It represented 2% of the applied P fertilizer content of both sites.  This indicates that paddy cultivation under both the conditions does not pose a threat to water quality of the nearby water bodies if the farmers adhere closely to the Department of Agriculture recommended fertilizer schedules.

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Keywords :

Leaching, Paddy, Phosphate.

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