CONCURRENT TRANSFORMATION OF LIGNOSULFONATE CARBON AND UREA NITROGEN IN CLAY SOIL

Lignosulfonate (LS), a waste product from the pulp and paper industry, can be a potential source of soil organic matter. Its transformation in soil may affect the relative amounts of soil N and organic matter fractions. A clay soil was incubated with urea at rates of 0, 500, or 1000 mg N kg-1 soil and NH4LS at rates of 0, 25, 50, 100, or 150 g NH4LS kg-1 soil at 70% field moisture capacity for 60 d. The incubated soil was analyzed for NH4-N, NO3-N, and total N. Soil organic carbon was partitioned into humin (HM)C, humic acids (HA)C, and fulvic acids (FA)C. In general, both urea and NH4LS additions increased total N, NH4-N, and organic N (difference between total N and NH4-N) but reduced NO3-N. The higher the NH4LS rate, the greater the regression slope of N fractions (except NO3-N) on urea addition rates, and the higher the urea rate, the greater the regression slope of N fractions (except NO3-N) on NH4LS rates, indicating the effect of interaction between urea and NH4LS on N distribution in the soil. Ammonium LS increased and urea decreased the C/N ratio of soil organic matter. Proportions of HM-C and RA-C decreased while that of FA-C increased with increasing NH4LS rates. Urea reduced the HA-C and increased the FA-C fraction. The results showed that simultaneous application of urea and NH4LS can increase soil organic matter content (particularly the FA-C fraction) and enhance N transformation into NH4-N and organic N fractions and reduce NO3-N.