Defoliation management of forage species in the northern USA is related to total nonstructural carbohydrate (TNC) concentrations. These energy compounds are closely related to winter survival, stand persistence, and subsequent productivity of stands. Influences of early spring defoliation on TNC concentrations of switchgrass ( Panicum virgatum L.) during recovery growth in the humid USA have not been reported. This field study was conducted to observe influences of defoliation time and intensity on TNC concentrations during recovery growth when switchgrass was grown without or with N fertilization (120 kg N ha −1 ). The experimental site was a Webster‐Nicollet soil complex (fine‐loamy, mixed, mesic Typic Haplaquolls‐Aquic Hapludolls). Defoliation treatments at 2‐wk intervals in 1984 and 1985 consisted of early‐, mid‐, and late‐spring defoliation, each at moderate or severe intensity. Nitrogen fertilization reduced TNC concentrations for all defoliation treatments. Accumulated TNC concentrations remained lower after 3, 6, and 9 wk of recovery growth for 120 compared with 0 kg N ha −1 , but relatively little difference was observed among defoliation treatments in TNC concentrations by mid‐October. Severe defoliation at early, mid, and late spring generally contributed to lower TNC concentrations during recovery growth compared with moderate defoliation. However, TNC concentrations 6 to 8 wk or less after spring defoliation were at a relatively high concentration for most defoliation treatments, which suggests that herbage utilization in mid‐ to late‐July should not seriously weaken stands. Lower TNC concentrations in mid‐October of 1985 compared with 1984 suggest that both weather conditions and defoliation management influence TNC concentrations in stem bases of switchgrass.
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George et al. (1989) studied this question.