ROOT AND SHOOT RESPONSES OF SAND BLUESTEM TO DEFOLIATION

Knowledge of root response, as well as shoot response, to defoliation is needed to manage grasslands in environments where water and/or nutr ients are limiting. The objective of this study was to document the re sponse of sand bluestem (Andropogon hallii Hack) roots and shoots to d ifferent times and Frequencies of defoliation. Individual sand blueste m plants were grown in 15 X 100-cm polyvinyl chloride (PVC) containers which were placed in the plants' natural setting. Twelve plants (repl ications) were clipped to a 7-cm stubble height during mid-month for e ach of the following defoliation schedules: 1) June July, and August; 2) June and August; 3) June; 4) July; 5) August; and 6) October. The O ctober defoliation, after shoot senescence, served as the control Mult iple defoliations reduced (P < 0.05) root weight, root area, root leng th, and weight of total nonstructural carbohydrates (TNC) in roots by an average of 33, 42, 43, and 34%, respectively, compared to control p lants. A single defoliation in June only reduced root weight, root are a, root length, and weight of TNC in roots by 14, 19, 16, and 13%, res pectively, compared to control plants. Defoliating plants during the g rowing season did not affect (P > 0.05) number of tillers, weight per tiller, above-ground weight, number of buds, weight of rhizomes, or we ight of TNC in rhizomes. Grazing sand bluestem more than once during t he growing season may reduce root growth and diminish its ability to c ompete for water and nutrients. Grazing during the dormant season or o nce during the early part of the growing season should be least detrim ental to sand bluestem.