Yellow foxtail [Setaria glauca (L.) Beauv.], giant foxtail (Setaria faberi Herrm.), giant green foxtail [Setaria viridis var. major (Gaud.) Posp.], robust white foxtail (Setaria viridis var. robusta-alba Schreiber), and robust purple foxtail (Setaria viridis var. robusta-purpurea Schreiber) were grown from seed in pure stands in sand-soil nutrient solution cultures at various nitrogen levels. Within taxa dry weight of herbage differed significantly with nitrogen level, but dry weight of roots did not. Yellow foxtail produced more leaf area than the other four taxa regardless of nitrogen level. At the low nitrogen level, yellow foxtail produced significantly more root mass (dry weight) than the other taxa; giant foxtail was second in root-mass production. The order of root-mass production was the same at medium and high nitrogen levels, but only at a 12-h photoperiod. At a 16-h photoperiod, root production was equal in yellow foxtail and giant foxtail and was significantly greater in these taxa than in giant green foxtail, robust white foxtail, or robust purple foxtail. Generally similar relationships were evident in the root: shoot ratios. The chances for survival with giant foxtail taxa should be better for yellow foxtail than for the other foxtail taxa since yellow foxtail produced more root mass even at low nitrogen fertility, a condition common in undistrubed sites such as roadsides and fencerows.
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