EFFECTS OF CALCIUM LIGNOSULFONATES ON UREA HYDROLYSIS AND NITRIFICATION IN SOIL

The increases in urea consumption in crop production have encouraged r esearch activities evaluating various materials as potential urease an d nitrification inhibitors. This report presents results of three expe riments testing lignosulfonate (LS), a waste product of the pulp and p aper industry, as a urease and nitrification inhibitor. The first expe riment was for urea hydrolysis in a clay soil with or without bulk-dig ested (BD) or sugar-free (SF) calcium lignosulphonate (CaLS). The seco nd experiment studied the effect of BD on jack bean urease activity in solution. The third experiment evaluated the effect of BD or SF on ch anges in soil NO3- content. Calculation of half-life times of urea sho wed that application of either BD or SF reduced urea hydrolysis in the soil at high rates, with SF being more effective than BD. The decreas es in urea hydrolysis were attributed to inhibition of urease activity by LS as indicated by the solution incubation experiment. After incub ation for 24 h, 80% urea remained in solutions with simultaneous addit ions of jack bean urease and BD, compared with 20% in solutions withou t BD. For incubation of the soil without urea, NO3-N contents with LS additions were 0.5 to 10.1% of that without LS, and NO4-N contents wer e significantly higher than NO3-N contents. Low NO3-N content after in cubation of the soil with LS was attributed to immobilization by micro bes, inhibition of nitrification, and possibly induced denitrification of native NO3- by sugars added with LS.