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Nitrogen Movement Resulting from Surface Application of Liquid Sewage Sludge¹

ABSTRACT

One of the factors limiting the rate at which sewage sludge can be applied to soil is the speed at which inorganic N is formed and the fate of that inorganic N. A greenhouse lysimeter study was initiated in order to quantify some of the sinks into which N from sludge applications might move. For 12 weeks soil columns were treated at 3-week intervals with a surface application of 2.5 cm of liquid sewage sludge. During each 3-day interval 2.5 cm of water was applied to: (i) soil receiving no sludge (Soil-2.5), (ii) soil receiving sludge (Sludge-2.5), and (iii) soil planted to Coastal bermudagrass (Cynodon dactylon L. Pers.) receiving sludge (Grass-2.5). Five centimeters of water was added to soil + grass + sludge (Sludge-5) during each 3-day interval. Another treatment was used to encourage a nitrification-denitrification cycle. This treatment (Grass-F) was identical to Grass-2.5 except that during each third week sufficient water was added to bring the 3-week total to the same as that in Grass-5. Provisions were made to collect the leachate for NO₃-N analysis and to measure NH₃ volatilization from the sludge.

The average loss of N as NH₃ was 36% of the applied NH₄-N in the Soil-2.5 treatment and 24% in the three grass treatments. This represented 4.9 and 3.3%, respectively, of the total N applied. The Grass-5 treatment resulted in the maximum NO₃-N leaching loss (5.4% of the applied N). The Grass-F treatment did not result in reduced NO₃-N leaching. Grass removed 10.3% of the applied N. From 52 to 64% of the applied N remained in the sludge crust on the soil surface.

Key Words: nitrate leaching • NH₃ volatilization

¹ A contribution from the Univ. of Georgia Agr. Exp. Sta., College Station, Athens, 30602.

² Formerly Graduate Research Assistant, Agron. Dep., Univ. of Georgia, presently Agronomist, TVA, Muscle Shoals, Ala. 35660 and Professor of Agronomy, Univ. of Georgia, Athens, respectively.