Land Disposal of Liquid Sewage Sludge: III. The Effect on Soil Nitrate
1972
King, Larry D. | Morris, H. D.
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.
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