Effects of Clipping on Growth and Physiology of ‘Merion’ Kentucky Bluegrass1

Abstract

Reduced growth and vigor caused by close and frequent clipping is a common problem in turfgrass culture. The objectives of this study were to evaluate the effects of clipping on the growth and physiology of ‘Merion’ Kentucky bluegrass (Poa pratensis L.). Using a controlled environment (23°C day and 16°C night), uniculm seedlings were grown from seed in pots for an 8‐week establishment period. These plants were then cut at 2.5 and 6.2 cm at a frequency of semiweekly (3 to 4 days), weekly, and biweekly, and compared with a control that was not clipped. Plant responses to clipping were measured at 0 to 2, 2 to 4, and 4 to 6 week intervals after the first clipping. Dry weight of roots and regrowth of shoots following clipping were greater in plants frequently cut at 2.5 cm than in plants infrequently cut at 6.2 cm. Lateral stem formation (tillers plus rhizomes) was greater or similar in plants cut biweekly than semiweekly at both cutting heights. Root:shoot (sheath plus blade tissue) ratios were generally greater in plants cut semiweekly than weekly or biweekly at both cutting heights. Plants clipped frequently had in most cases greater 14C‐photoassimilate accumulation in the root and sheath fractions and less accumulation in the blade fraction than plants clipped infrequently. Rat~s of apparent photosynthesis and dark respiration per unit leaf area were generally higher in plants cut semiweekly than biweekly; whereas, these same parameters based on a total leaf area were lower in plants cut semiweekly than biweekly. Reduced growth and vigor associated with close and frequent clipping in Merion Kentucky bluegrass is attributed to loss of leaf area. Based on these findings, altering clipping frequency may be a mo:re effective means of reducing the detrimental effects of clipping in Merion Kentucky bluegrass than adjustments in cutting height.