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This article in AJ

  1. Vol. 88 No. 4, p. 536-540
    Received: Sept 13, 1995

    * Corresponding author(s): dlg@soilwater.agr.okstate.edu
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Nitrate Dynamics Following Brush Control in a Post Oak-Blackjack Oak Forest

  1. David L. Gay ,
  2. Earl R. Allen,
  3. David M. Engle and
  4. Jimmy F. Stritzke
  1. Dep. of Agronomy, Okla. State Univ., Stillwater, OK 74078



Converting marginal hardwood forests to grass may increase economic output from livestock production. Nitrogen dynamics during conversion need to be evaluated to determine if conversion releases excessive quantities of NO3-N, with potential adverse effects on the environment. This study was conducted to determine the amount of NO3-N present during conversion of a mature post oak-blackjack oak (Quercus stellata Wangenh.-Q. marilandica Muenchh.) forest and to identify optimum time periods for grass uptake of available mineralized N after herbicide treatment. Four treatments were evaluated: (i) no brush kill with no grass overseeding, (ii) brush kill with no grass overseeding, (iii) brush kill with cool-season grass overseeding, and (iv) brush kill with warm-seasong rass overseeding. The cool-season (C3) grass was ‘K-31’ tall fescue (Festuca arundinacea Schreb.); ‘Plains’ Old World bluestem [Bothriochloa ischaemum var. ischaemum (L.) Keng] was the warm-season( C4) grass. Soil profile NO3-N to a depth of 60 cm and NO3-N concentrations in soil leachate at 60 cm were measured in 15- by 25-m plots during a 22-mo period (June 1993 to March 1995). Soil NO3-Nin creased from ì5 kg ha−1 initially to >50 kg ha−1 when brush was killed with tebuthiuron [N-[5-(1,1-dimethylethyl)- 1,3,4-thiadiazoi-2-yl]-N,,N′-dimethylurea] application. Soil and leachate NO3-Nin tall fescue overseeded plots returned to near pretreatment levels by the end of the first rapid growth phase of tall fescue in June 1994. Soil NO3-Nin Old World bluestem overseeded and unseeded brush kill plots remained elevated throughout the experiment, and leachate NO3-N concentrations rose from 0 to more than 70 mg L−1 The risk of NO3-N leaching after brush control is reduced by overseeding with tall fescue.

Research supported by the OklahomaS tate Univ. Ctr. for Water Research and the Oklahoma Agric. Exp. Stn. through Project no. S-2044 and is approved for publication by the Director of the OklahomaA gric. Exp. Stn.

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