Effect of nitrapyrin rate on nitrification in soils having different organic matter contents1
1987
CHANCY, H. F. | Kamprath, E. J.
Due to possible large losses of nitrate N from the rooting zone, N fertilizer application for corn (Zea mays L.) is usually supplied as split applications in the south-eastern United States. Nitrapyrin (NI) is a nitrification inhibitor that has the potential of reducing nitrate N losses and possibly allowing all the N to be applied preplant. However, increasing soil organic matter content decreases the effectiveness of NI. We conducted experiments to determine the rate of NI required to inhibit nitrification of broadcast applications of 100 kg N/ha as urea in soils with different organic matter contents.Soils and their organic matter contents used in this research were a Roanoke loamy sand (clayey, mixed, thermic Typic Ochraquult) of 1.9 g kg OM, Cape Fear loam (clayey, mixed, thermic, Typic Umbraquult) of 61 g kg OM, and a Conaby muck (coarse, loamy, mixed, nonacid, thermic Histic Humaquept) of 163 g kg OM.When NI was not included, nitrification of the applied N was complete by 14 d in the Roanoke and Cape Fear soils and at 21 d in the Conaby soil. To inhibit nitrification for 35 d, rates of 2.24 and 8.96 kg NI/ha were required on the Roanoke and Cape Fear soils, respectively. After 35 d with the Conaby soil, there was no effect on nitrification with rates up to 8.96 kg NI/ha. Nitrapyrin effectiveness is thought to be reduced due to its sorption by organic matter. These data suggest that higher NI rates are required to reduce nitrification of ammonical N as soil organic matter content increases.
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