Differential Mobility of Nitrapyrin and Ammonium in a Sandy Soil and Its Effect on Nitrapyrin Efficiency1

Nitrification inhibition by 2‐chloro‐6‐(trichloromethyl) pyridine (nitrapyrin) has not been consistent on sandy soils. This study was conducted to evaluate movement of nitrapyrin and N in a fine sand as influenced by water rate and leaching period. In greenhouse studies, nitrapyrin reduced NO8‐N loss from a Kanapaha fine sand (loamy, siliceous, hyperthermic Grossarenic Paleaquult) for only the first 2 weeks of a 5‐week leaching period. In segmented soil columns, nitrapyrin was placed in the soil at a depth from 13 to 15.5 cm. After the soil was leached at water rates of 0, 2.5, and 5 cm/week for 2 and 4 weeks, soil samples were incubated with NH4‐N. Nitrification bioassay of soil above and below nitrapyrin placement showed that nitrapyrin movement was affected more by volatility than by water rate. Movement of NH4‐N from a 13.0 to 15 cm depth was studied in soil columnsthat contained 20 ppm nitrapyrin in the soil. After leaching, NH4‐N and NO3‐N levels were determined at various soil depths. With increases in the rate of water applied and in the leaching period, higher levels of NH4‐N moved to lower depths than nitrapyrin. Movement of NH4‐N away from nitrapyrin may account for the reduced nitrapyrin effectiveness often observed for sandy soils.