• Open Access

Seasonal nitrogen dynamics of Miscanthus×giganteus and Panicum virgatum

Authors

  • EMILY A. HEATON,

    1. Department of Crop Sciences, University of Illinois, 1201 W. Gregory Drive, 379 Madigan Lab., Urbana, IL 61801, USA,
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    • 1Current address: Department of Agronomy, Iowa State University, 1403 Agronomy Hall, Ames, IA, USA, e-mail: heaton@iastate.edu

  • FRANK G. DOHLEMAN,

    1. Department of Plant Biology, University of Illinois, 1201 W. Gregory Drive, 379 Madigan Lab., Urbana, IL 61801, USA,
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  • STEPHEN P. LONG

    1. Department of Plant Biology, University of Illinois, 1201 W. Gregory Drive, 379 Madigan Lab., Urbana, IL 61801, USA,
    2. Institute for Genomic Biology, University of Illinois, 1206 W. Gregory Drive, Room 126 IGB. Urbana, IL 61801, USA
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Stephen P. Long, tel. +1 217 333 2487, fax +1 217 244 7563, e-mail: slong@uiuc.edu

Abstract

There is a tradeoff to consider when harvesting perennial biomass crops: harvest too late and yield declines, harvest too early and risk higher mineral contents, particularly nitrogen (N). Allowing the crop to completely senesce and recycle nutrients has several advantages, including improved feedstock quality and reduced fertilizer requirements, but it comes at a risk, particularly in temperate climates where snow and ice can reduce or destroy harvestable biomass. The effect of harvest time on the N concentration ([N]) and biomass of Panicum virgatum and Miscanthus×giganteus was evaluated at three sites in Illinois over two years. In both species [N] of standing biomass significantly declined with time (P<0.0001). Interestingly, there was no significant interaction effect of species and sample date on [N] (P=0.2888), but there was a highly significant interaction effect on the total N in standing biomass (P<0.0001). The amount of standing N was directly related to biomass yield. Seasonal changes in standing N differed among locations, suggesting that harvest time recommendations for N management depend on location. P. virgatum would have potentially removed as much as 187 kg N ha−1 if harvested green, and as little as 5 kg N ha−1 if harvested in late winter. Because of higher biomass yields, M. ×giganteus standing N ranged from 379 kg N ha−1 in June to <17 kg N ha−1 in February. Importantly, there was little overall change in [N] between an early winter (December) harvest and a late winter (February/March) harvest, indicating the benefits of N cycling in the system can be realized by end of the growing season and thus, at least from an N economy perspective, there is no reason to risk yield losses by delaying harvest over the winter.

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