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Surface Runoff Losses of Fertilizer Elements¹

ABSTRACT

Surface runoff losses of fertilizer N, P, and K were measured from a Loring silt loam soil with an average slope of 5%. Plots seeded to pearl millet (Pennisetum typhoides [Burm.]) in 1973 and 1974 were fertilized at the rate of 112-49-93 kg/ha of incorporated N, P, and K using two different fertilizer blends, a 33.3-8.7-16.6 and an 8-3.5-6.6. The percent of water-soluble fertilizer elements lost in 1973 from the higher and lower blend concentrations, respectively, were N, 0.50 and 0.30%; P, 0.14 and 0.06%; and K, 0.67 and 0.92%. In 1974, N losses were 0.89 and 0.41%; P, 0.35 and 0.20%; and K, 0.42 and 0.35%. Precipitation during the experimental periods was 20.40 cm in 1973 and 11.03 cm in 1974. Two of the millet plots were then topdressed with NH₄NO₃ fertilizer at the rate of 112 kg N/ha. Topdressed fertilizer-N losses were 2.68% in 1973 and 1.82% in 1974. Precipitation during these second tests was 27.97 cm in 1973 and 27.69 cm in 1974. Ryegrass (Lolium multiflorum L.) plots were fertilized with sulfur-coated urea (SCU) and uncoated urea (U) at the rate of 224 kg N/ha during the growing seasons of 1973 and 1974. Total N losses (U vs. SCU) were 9.52 and 0.26% in 1973, and 1.67 and 0.42% in 1974. Precipitation was 23.89 cm in 1973 and 29.57 cm in 1974. A 10.08-cm rainfall on the third day of the test in 1973 caused almost three-fourths of the 9.52% N lost from the uncoated urea to be lost in that runoff and while it was still in the urea form. The sulfur coating prevented large surface losses of N from the SCU.

Key Words: nitrogen • phosphorus • potassium • water quality • environmental pollution

¹ Contribution from the Agron. Dep., Louisiana Agric. Exp. Stn., Louisiana State Univ., Baton Rouge, LA 70803.

² Associate Professor, Former Graduate Assistant, and Professor, respectively.

Received for publication October 28, 1975.