Soil Nitrogen Availability following Long-Term Burning in an Oak-Hickory Forest
1984
Vance, Eric D. | Henderson, Gray S.
Seasonal levels of extractable ammonium and nitrate in the surface soil of oak-hickory (Quercus spp. and Carya spp.) forest plots subjected to 30 yr of annual and periodic (4-yr) prescribed burning were studied. Laboratory incubations were also carried out for 4-, 14- and 28-d periods at each of six dates to determine the effect of the burning treatments on mineralizable N. Ammonium was the predominant N form regardless of treatment. Burning significantly (P = 0.05) reduced quantities of extractable NH⁺₄ over all sampling dates, with annual burning resulting in lower amounts than burning every 4 yr. Burning also significantly reduced the quantity of N mineralized during incubation. Since previous studies have not shown decreases in total N on the burned plots, the lower extractable N concentrations appear to be the result of an adverse effect of long-term burning on substrate quality that reduced rates of mineralization. The treatment influence on mineralizable N was more apparent during the latter 24 d of laboratory incubation, whereas the initial 4 d reflected the influence of sampling date to a greater degree. From this pattern, it is hypothesized that the initial 4 d of incubation are more indicative of field environmental conditions, whereas the latter 24 d reflect the quantity of mineralizable substrate present. Although treatment differences in extractable and mineralizable N were statistically significant overall, the lack of statistical differences at some dates indicates the importance of seasonal sampling.
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