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Land Disposal of Liquid Sewage Sludge: III. The Effect on Soil Nitrate¹

ABSTRACT

A field experiment was conducted over a 2-year period to determine the effect of liquid sewage sludge on soil nitrate content of a Cecil sandy clay loam (Typic Hapludults) to a 120-cm depth. Periodic applications of four rates of sludge to coastal bermudagrass (Cynodon dactylon L. Pers.) supplied a total of 4.4, 8.8, 10.0 and 20.0 cm of sludge in 1969 and 2.5, 5.0, 10.0, and 20.0 cm in 1970. Respective amounts of N applied by the four rates were 1,037, 2,074, 2,580, and 5,160 kg/ha in 1969 and 492, 984, 1.970, and 3,940 kg/ha in 1970. A chemical fertilizer treatment supplied 364 kg/ha of N in 1969 and 489 kg/ha in 1970. The two highest sludge rates affected significant increases in soil nitrate in the 0- to 120-cm profile. The other two sludge rates and the chemical fertilizer treatment did not increase soil nitrate and were deemed safe from the standpoint of potential groundwater pollution. At the 20-cm rate 40% (287 kg/ha) of the NO₃-N present in the 0- to 120-cm profile in October 1970 could not be accounted for the following May. Of the N supplied by the 10- and 20-cm applications, 17 and 9%, respectively, was recovered through crop uptake while 56 and 54% remained in the sludge crust that had accumulated on the soil surface.

Key Words: nitrogen balance • denitrification • pollution

¹ Contribution of the Univ. of Georgia Agr. Exp. Sta., College Station, Athens, Georgia 30601.

² Formerly graduate research assistant, Agronomy Dep., Univ. of Georgia, presently post doctoral fellow, Dep. of Land Res. Sci., Univ. of Guelph, Guelph, Ontario, and Professor of Agronomy, Univ. of Georgia, Athens, Georgia, respectively.

Received for publication February 25, 1972.