No abstract

Heavy-metal inhibition of nitrification in soils treated with reformulated nitrapyrin was investigated. Clarion and Okoboji soils were treated with ammonium sulfate [(NH 4 ) 2 SO 4 ] and a nitrification inhibitor. Copper(II) (Cu), Zinc(II) (Zn), Cadmium(II) (Cd), or Lead(II) (Pb) were added to each soil. A first-order equation was used to calculate the maximum nitrification rate (K max ), duration of lag period (t 0 ), period of maximum nitrification (Dt), and the termination period of nitrification (t s ). In the Clarion soil, the K max decreased from 12 mg kg 21 d 21 without the nitrification inhibitor to 4, 0.25, 0.86, and 0.27 mg kg 21 d 21 , respectively, when the inhibitor and Cu, Zn, Pb, or Cd were applied. In the Okoboji soil, K max decreased from 22 mg kg 21 d 21 with no inhibitor to 6, 3, 4, and 2 mg kg 21 d 21 , respectively, when an inhibitor and Cu, Zn, Pb, or Cd were added. The t 0 varied from 8 to 25 d in the Clarion soil and from 5 to 25 d in the Okoboji soil, due to addition of Cu, Zn, Pb, or Cd and the inhibitor.

The effects of temperature and water potential on nitrification were investigated in two Iowa soils treated with Stay-N 2000. The soils were incubated at 10, 20, and 30 uC after soil water potentials of 21, 210, or 260 kPa were applied to each soil. A first-order equation was used to calculate the maximum nitrification rate (K max ), duration of lag period (t9), period of maximum nitrification (Dt), and termination period of nitrification (t s ). The highest K max were 18 and 24 mg kg 21 d 21 nitrate (NO 3 2 )-nitrogen (N), respectively, at 30 uC and 210 kPa in both the Nicollet (fine-loamy, mixed, superactive, mesic Aquic Hapludoll) and Canisteo (fine-loamy, mixed, superactive, calcareous, mesic Typic Endoaquoll) soils and reduced to 4 and 16 mg kg 21 d 21 NO 3 2 -N when Stay-N 2000 was added. The extension of t9 due to the addition of Stay-N 2000 was as high as 7 d in the Nicollet soil at 10 uC and 21 kPa and as little as 2 d in the Canisteo soil at 20 uC and 210 kPa.

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