Nitrogen Movement Resulting from Surface Application of Liquid Sewage Sludge

Abstract

AbstractOne 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.