Where a substantial thatch layer exists, new roots and stem growth from plant crowns occurs, at least initially, within the thatch. In some turfs, very little rooting may occur in the soil underlying the thatch. Therefore, under these conditions it appears that the thatch serves a greater role as a plant‐holding matrix and a growth medium while the soil's role decreases. The objective of this study was to determine the bulk density, total porosity, moisture characteristics, and organic matter contents of thatch and surface soils of thatched and thatch‐free Kentucky bluegrass (Poa pratensis L.) sites.
The evaluation methods included: 1) the core method for measuring bulk density; 2) air pycnometric determination of total porosity; 3) a modified pressure plate procedure utilizing Tempe cells for determining moisture extraction curves; and 4) organic matter content on the basis of weight loss upon ignition. Bulk density of thatch was significantly lower than soil, but varied between thatch samples depending on the amount of soil within the thatch. Total porosity of thatch samples was not significantly different, but was greater than soil porosity. Moisture retention of thatch at low water potentials was less than the surface soil from thatch‐free sites, indicating that most of these pores are macro‐size pores. This study suggests that cultural practices, such as irrigation, may need to be modified to sustain aesthetic turf where thatch is a predominant component of the edaphic environment.
Epidemiologic studies of pesticides have been subject to important biases arising from exposure misclassification. Although turf applicators are exposed to a variety of pesticides, these exposures have not been well characterized. This paper describes a repeated measures study of 135 TruGreen applicators over three spraying seasons via the collection of 1028 urine samples. These applicators were employed in six cities across the United States. Twenty-four-hour estimates (μg) were calculated for the parent compounds 2,4-D, MCPA, mecoprop, dicamba, and imidacloprid and for the insecticide metabolites MPA and 6-CNA. Descriptive statistics were used to characterize the urinary levels of these pesticides, whereas mixed models were applied to describe the variance apportionment with respect to city, season, individual, and day of sampling. The contributions to the overall variance explained by each of these factors varied considerably by the type of pesticide. The implications for characterizing exposures in these workers within the context of a cohort study are discussed.
The effects of five preemergence herbicides on turfgrass quality and control of crabgrass (Digitariaspp.) were measured to determine the influence of thatch on preemergence herbicide activity in Kentucky bluegrass (Poa pratensisL.) turf. Field applications of benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin -5-one], and prosulfalin {N-[[4-(dipropylamino)-3,5-dinitrophenyl] sulfonyl]-S,S-dimethylsulfilimine} to thatchy Kentucky bluegrass turf in spring caused injury that was apparent during periods of summer stress, while DCPA (dimethyl tetrachloroterephthalate) and bensulide [O,O-diisopropyl phosphorodithioateS-ester withN-(2-mercaptoethyl)benzenesulfonamide] caused little or no injury. The same treatments on thatch-free sites revealed that only prosulfalin was injurious. Adsorption of benefin, bensulide, and DCPA from solution was greater by thatch than by soil; however, the mobility of these herbicides in undisturbed thatch profiles was greater than measured in undisturbed surface soil from thatch-free sites. Thus, turfgrass injury from preemergence herbicides on thatchy sites is due to at least two factors: the greater mobility of preemergence herbicides in thatch than in soil; and the inherent susceptibility of Kentucky bluegrass to injury from preemergence herbicides that come into direct contact with roots and other absorbing organs.
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