Thatch Influence on Mobility and Transformation of Nitrogen Carriers Applied to Turf1

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Abstract
Thatch frequently exists as part of the edaphic environment of a turfgrass community and thus, should be considered when attempting to determine the fate of topically applied fertilizers in turf. The purpose of these investigations was to determine the influence of a thatch layer on the vertical mobility and transformation of soluble and slowly soluble N carriers following application.Measurements of N leaching, retention, and volatilization were made using cores of thatch and Flanagan silt loam (Aquic Argiudoll) soil extracted from fieldgrown turf of Kentucky bluegrass (Poa pratensis L.). Urea was selected as the soluble N carrier, and isobutylidene diurea (IBDU) was the slowly soluble N carrier. Application of urea resulted in 2.5 times as much N leaching and correspondingly lower N retention, in thatch than in soil. Where IBDU was used as the N source, leaching from the thatch was reduced from 81 to 5% of the applied N, and leaching from the soil was reduced from 32 to 23% compared to urea‐treated cores. In the volatilization studies, 39% of the applied N from urea was lost as ammonia from thatch cores compared to only 5% from the soil cores. Where IBDU was the N source, little N volatilization (4% from thatch, 2% from soil) occurred. In conclusion, where a substantial thatch layer exists, and turfgrass rooting is largely confined to the thatch layer, use of a slowly soluble N carrier might be preferable over soluble urea for reducing N losses due to leaching and volatilization. As an alternative, effective measures for controlling the thatch may result in greater efficiencies in the use of fertilizer N by the turfgrass community.