Distribution of water-soluble carbohydrate reserves in the stubble of prairie grass and orchardgrass plants

A greenhouse study was undertaken to investigate the distribution of water-soluble carbohydrates (WSC) within the lower 100 mm of 'Kara' orchardgrass (Dactylis glomerata L.) and 'Matua' prairie grass (Bromus willdenowii Kunth.) stubble through four distinct regrowth cycles. Water-soluble carbohydrate levels were consistently higher in prairie grass tillers compared with orchardgrass tillers. A decrease in WSC levels with increasing stubble height was observed for vegetative tillers of both species. However, the WSC concentration gradient was better defined for orchardgrass, with a clear decrease in WSC concentration between the 21- to 30- and 31- to 40-mm segments, and 77% of WSC content contained within the O- to 30-mm stubble height range (with 0 mm representing the base at ground level). The WSC concentration gradient for prairie grass was less clearly defmed, with a relatively high WSC concentration throughout the 0- to 100-mm stubble height range. There was a trend for decreasing WSC concentration between the 31- to 40- and 41- to 50-mm segments, with 62% of WSC content contained within the 0- to 40-mm stubble height range. These results suggest that the previously adopted defoliation stubble height of 45 to 50 mm, which is the optimal defoliation management for perennial ryegrass (Lolium perenne L.), maintains over 60% of stubble WSC reserves and therefore should not he detrimental to the persistence of orchardgrass and prairie grass. While decreasing defoliation height to 30 mm may be acceptable for orchardgrass, prairie grass is more sensitive to defoliation severity, with defoliation below 45 mm not recommended. © American Society of Agronomy.