N Losses in Irrigation Return Flows from Flooded Rice Plots Fertilized with Ammonium Sulfate1,2
- I. M. Bilal,
- D. W. Henderson and
- K. K. Tanji3
Losses of N from fertilized croplands are of concern from standpoints of fertilizer use efficiency as well as potential water pollution. Field experiments were conducted to evaluate the discharge of inorganic N in surface irrigation runoff and seepage in 7.6 ✕ 67 m test plots cropped with paddy rice (Oryza sativa L., cultivar Earlirose). Cultural practices commonly used in rice production in California were imposed on three plots and extensively monitored from planting to harvest. Plots 1 and 2 were continuously flooded throughout the growing season while Plot 3 was oncedrained in the 5th week after planting for a 1-week period. Granular (NHL4)2SO4 was applied at a rate of 168 kg N/ha to all plots but the mode of application and timing differed. In Plot 1 the fertilizer was partly soil-incorporated and partly soilbroadcast before seeding and flooding. In Plots 2 and 3, 112 kg N/ha was soil-incorporated before planting and 56 kg N/ha was top-dressed in the floodwater in the 6th week after planting.
The seasonal water application varied from 454 to 530 cm of which 104 cm was lost as evapotranspiration, 204 to 219 un as surface runoff, and, by difference, 128 to 222 un as seepage losses. The total seasonal losses of N from both the irrigation runoff and seepage were 18.6, 36.4. and 30.2 kg N/ha for Plots 1, 2, and 3 or 11, 22 and 18% of the applied fertilizer, respectively. The seep age losses were 45, 61, and 70% of the total seasonal N losses in Plots 1, 2, and 3, respectivelyPlease view the pdf by using the Full Text (PDF) link under 'View' to the left.
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