Thatch and soil characteristics of cool- and warm-season turfgrasses

Turfgrass thatch development is a direct consequence of an imbalance between growth and decomposition of organic residues. This study was conducted to determine the characteristics of thatch and the underlying soil in a three-year-old stand of Southshore creeping bentgrass (Agrostis palustris Huds.) and a six-year-old stand of Meyer zoysiagrass (Zoysia japonica Steud.). Intact thatch + soil cores were randomly collected from the two sites for thatch and soil bulk density and total porosity determinations. Disturbed samples of thatch and soil were processed and analyzed for total microbial biomass carbon (C); basal and specific maintenance respiration rates; total C, nitrogen (N) and hydrogen (H) contents; easily mineralizable, soluble, oxidizable and lignin C fractions, and organic matter quality. While the total microbial biomass C content and basal respiration rates were higher in thatches, the specific maintenance respiration rates were significantly lower in soils. Total, soluble, oxidizable and lignin C, and total N and H contents were significantly greater in thatches than in soils. Although the absolute amounts of soluble and oxidizable C contents were smaller in soil than in the thatch, the soluble and oxidizable C as fractions of total C were significantly lower in thatches than in soils. The bentgrass thatch contained more microbial biomass and lignin Q than the zoysiagrass thatch. Both thatches had lower bulk densities and higher total porosities than the underlying soils. Spectrophotometric analyses suggested an accumulation of finer size organic matter in the bentgrass thatch than in the zoysiagrass thatch. An increase in microbial biomass and total C, but a substantial decrease in specific maintenance respiration rates, suggest that thatch development under turf may be acting as a C sink. A decline in microbial biomass and total C contents, but significant increases in specific maintenance respiration rates, suggest that soils under thatch may be serving as sources of CO2 to the troposphere. The effect was more pronounced at the zoysiagrass site than at the bentgrass site.