EFFECTS OF SELECTED SOIL FUNGICIDES ON NITRIFICATION AND GROWTH OF PRIVET IN A PINE BARK MEDIUM

Nitrification inhibitors were evaluated for their capacity to retard oxidation of ammonium in a pine bark medium. Nitrapyrin, captan, etridiazole, and metalaxyl were added to a pine bark medium in amounts ranging from none to 133% of manufacturers' or research-based recommendations. Inhibition of nitrification was assessed by measurements of appearance of nitrate and disappearance of ammonium at 4-wk intervals for 12 wk. The effects of these chemicals on the growth and nitrogen (N) composition of privet (Ligustrum ibolium L.) in containers of pine bark mix were assessed. Based on retention of ammonium and suppression of nitrate accumulation, etridiazole and nitrapyrin were effective inhibitors, whereas captan and metalaxyl were not. Etridiazole was more effective than nitrapyrin, and the efficacy of etridiazole increased as amount of application increased. The efficacy lasted for about 4 wk with nitrapyrin or etridiazole. With the amounts of fertilization and inhibitors used, growth or total N concentrati...