Some Growth Characteristics of Four Old World Bluestems

Abstract

The growth dynamics of 4 Old World bluestem (Bothriochloa spp.) accessions were monitored in the field by periodic harvests of the aboveground biomass components (leaf blades, leaf sheaths plus enclosed stems, exerted stems plus inflorescences) during 2 growth cycles from April to September 1982. The first cycle extended from spring growth initiation (15 March) through flowering (6 July). The second cycle was initiated following the completion of the first by mowing the plants to a 50-mm stubble height and ended at flowering stage (20 September). Growth conditions during the first cycle were considered near optimum when precipitation was 1.71 of the long term mean and soil moisture averaged about 0.29 by volume. Temperatures during the second cycle were approximately 10 degrees C higher than during the first and precipitation was only 0.18 of normal. Soil moisture declined linearly throughout the second cycle and all accessions exhibited visual symptoms of drought stress. There were significant differences among accessions for most of the experimental parameters and accession ranking changed with the imposition of drought stress during the second cycle. Accessions with high relative growth rates were least tolerant of drought stress. Severe defoliation by clipping at the start of cycle 2 revealed 2 regrowth patterns which suggested potential differences in grazing tolerance. Two accessions tended to optimize canopy development by maximizing leaf area index while minimizing biomass and nitrogen investment per unit leaf area. The remaining 2 accessions produced fewer leaves with more investment per leaf. Lower relative growth rates of biomass and the ability to optimize canopy development following defoliation may result in a more stable forage source through time. Plants with these characteristics may not be top producers during periods of favorable growing conditions, but will likely maintain a level of performance under stress which compares more favorably with pre-stress performance.