Kinetics of nitrification in selected Iowa soils treated with Stay-N 2000
Nitrification rates were investigated in selected Iowa soils that differed in organic carbon contents, pH, and texture. This study was conducted to evaluate nitrification inhibition by reformulated nitrapyrin [2-chloro-6-(tricholoromethyl) pyridine] or Stay-N 2000 developed by Platte Chemical Co (Greeley, CO) applied to 10 g of surface soils representing Clarion, Nicollet, Canisteo, and Okoboji series treated with a solution containing 2 mg of N as ammonium sulfate (NH4) 2SO4. A nonlinear regression was used to determine nitrate accumulation. First order equations were used to calculate the maximum nitrification rate (Kmax), the duration of lag period (t '), the period of maximum nitrification (Deltat), and the termination period of maximum nitrification (t s). The course of nitrification varied among soils used. Stay-N 2000 appeared to be the better inhibitor to extend the period of maximum nitrification compared to nitrapyrin; and as good as nitrapyrin in reducing maximum nitrification rates in two soils studied. The effectiveness of a given rate of Stay-N 2000 enhanced in soils with high pH and organic C, such as in the Okoboji soil. At the rate of 12 mug a.i. g-1 soil Stay-N 2000 reduced the maximum nitrification rate an appreciable amount in the Okoboji soil. Nitrification rates in soils were also affected by the rates of N applied to these soils. The delaying effect of nitrification seemed to be associated with high concentration of NH4+-N. As one important factor in regulating nitrification is substrate availability, which is often limiting the growth of nitrifiers. The NO3--N accumulation increased with increasing temperature in all moisture levels applied in the study and reduced at the soil moisture level of -1 kPa. The highest maximum nitrification rate (Kmax) occurred at 30°C and at a moisture potential level of -10 kPa. All metals used in the study seemed to reduce Kmax in the Clarion and Okoboji soils. The overall process showed that the more the NO3--N accumulation, the higher the maximum rate of nitrification (Kmax) and the longer the delay period (t').