Root growth patterns of perennial ryegrasses under well-watered and drought conditions

Abstract

A boroscope and mini-rhizotrons were used to explore root growth patterns in five different ryegrasses grown outdoors under simulated field edaphic conditions including drought. Few major differences in root counts were found among the ryegrasses. The seasonal patterns of root counts in well-watered treatments showed an autumn peak that was later (or even suppressed) as autumn soil temperatures increased in consecutive years. Seasonal patterns were not measurable at more than 7 cm depth down the profile. The summer drought resulted in an increase in root counts right down the profile, which started about a month after the drought began. This was followed by rapid death of roots in the top 15 cm of soil but lower death rates deeper in the soil. After rewetting of the soil, there was a delay of approximately 1 month before a rapid increase in root production occurred. This overcame the apparent high soil temperature inhibition of autumn root growth in the well-watered control treatment.