Cutting Height and Frequency Effects on Composition, Yield, and Quality of a Bermudagrass-Crabgrass Mixture

Abstract

‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] is the most abundant warm-season perennial grass in the lower South. Large crabgrass [Digitaria sanguinalis (L.) Scop.] will often invade stands of Coastal bermudagrass but little is known about the response of this species mixture to defoliation management. A study was conducted in 1990 and 1991 to determine the effects that cutting height and interval have on species composition, dry matter (DM) yield and quality of a bermudagrass-crabgrass mixture. Percentage crabgrass, DM yield, crude protein (CP) and in vitro organic matter digestibility (IVOMD) were measured on small plots of coastal bermudagrass that were cut at three cutting heights (1, 4, and 7 in.) and five cutting intervals (1, 2, 3, 4, and 6 wk). Percentage crabgrass was low in 1990 and did not show a response to cutting height. Higher crab-grass percentages in 1991 showed a positive linear response to cutting height and a negative linear response to cutting interval at both the middle and end of the experiment. There was a linear decrease in DM yield as cutting height increased, but yield increased linearly with increased cutting interval. Crude protein percentage declined linearly with increased cutting interval, but a linear response to cutting height in both years changed from negative to positive as interval increased. There was a curvilinear increase of IVOMD as cutting height increased in both years. In 1990, there was a linear decrease of IVOMD as interval increased with the rate of decrease being higher as cutting height increased; however, in 1991, there was a curvilinear decrease of IVOMD with increasing interval. Results of this study indicate that cutting height and frequency interact to affect the productivity, quality, and composition of bermudagrass-crab-grass mixtures. Research Question ‘Coastal’ bermudagrass is extensively used in the lower South for both grazing and hay. Bermudagrass yield and nutritive value can be high; however, these attributes are greatly influenced by both cutting height and frequency. Crabgrass encroachment can further affect bermudagrass yield and quality. The objective of this study was to determine the effects of cutting height and interval on yield, quality, and botanical composition of a Coastal bermudagrass-crabgrass mixture. Literature Summary Several studies with Coastal bermudagrass have shown that reducing the frequency of harvests increases dry matter yield at the expense of forage quality. Other research has shown declines in yield and increases in quality as the cutting height increases. These studies, however, did not look at the combined effects of cutting height and frequency on yield and quality. Study Description A plot study was conducted in 1990 and 1991 with an existing stand Coastal bermudagrass. Location: East central Alabama Soil: Marvyn loamy sand (fine-loamy, siliceous, thermic, typic haplodult) Fertilization: N—150 lb/acre at start and midpoint P—44 lb/acre at start K—150 lb/acre at start and midpoint Irrigation: Applied weekly if necessary to provide 1 in./wk Cutting heights: 1, 4, and 7 in. Cutting frequencies: 1, 2, 3, 4, and 6 wk. Applied Questions How do bermudagrass-crabgrass mixtures respond to cutting height and frequency? In this study, the highest dry matter yields were obtained with a 6-wk cutting interval and 1-in. cutting height. Unfortunately, this treatment combination also resulted in the lowest crude protein and dry matter digestibilities. The highest quality forage was harvested at 1-wk intervals, with crude protein and in vitro organic matter digestibility tending to be higher for the 7-in. height at each interval. Thus, an alternative for improving the quality of bermudagrass hay could be to raise the cutting height. Trends in the yield and quality data indicate benefits in quality if heights are increased to 4 in. However, increases in quality with heights taller than 4-in. do not appear to be enough to offset the decline in yield. Can clipping management affect the botanical composition of a bermudagrass-crabgrass mixture? The two grasses responded differently to the cutting treatments. Crabgrass was most competitive with bermudagrass when the mixture was harvested frequently with a tall cutting height. Thus, cutting 1 in. above the soil surface at 4- to 6-wk intervals appears to provide bermudagrass with a competitive advantage.