| Abstrakt: |
Residue and its mode of placement in the soil are known to influence soil biological processes under certain conditions, including nitrification of applied ammoniacal fertilizers. In this experiment, the effect of straw placement on the nitrification of anhydrous NH3was studied in the laboratory. Gaseous NH3was line injected into Walla Walla silt loam at a 15‐cm depth, simulating a field application into soil: without straw, with the equivalent of 13.5 metric tons/ha of straw applied in a band at the 15‐cm depth and with straw, mixed uniformly in the surface 15 cm of soil. The NH3retention zone was sampled periodically for 10 weeks and analyzed for NH+1‐N, NO−2‐N, NO−3‐N, and soil pH. Air samples were withdrawn periodically from the soil systems for determining CO2and O2. Straw and its placement mode had little effect on the nitrification rate of the applied NH3. Presumably because of the large amount of straw in the retention zone, both the NH+1‐N and NO−3‐N concentrations were generally highest where the anhydrous NH3was injected directly into the straw band. However, the percentage of recovery of the applied N as NH+1‐N, by extraction with KC1, was only slightly higher from the banded straw treatment than for either the mixed straw or no‐straw treatments during the first 6 weeks of the experiment. This difference disappeared later. Differences in NO−3‐N recovery among treatments were small and not significant. Approximately 60% of the applied N had nitrified by the 10th week following N application. Oxygen and CO2concentrations indicated that adequate aeration prevailed throughout the incubation period with only minor differences among the treatments. Apparently any competitive effect by microorganisms for NH+4‐N in straw decomposition was eliminated by the high NH+4‐N concentrations in the NH3, retention zone, and the partial sterilization of the retention zone by the NH3did not affect nitrifying activity in the presence of straw differently than in residue‐free soil. |
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