Nitrate leaching and turf quality in established 'Floratam' St. Augustinegrass and 'Empire' zoysiagrass

The objectives of this research were to evaluate nitrate N (NO³-N) leaching and turf response to nitrogen rate (NR) and irrigation regime (IR) in 'Floratam' St. Augustinegrass ( [Walt.] Kuntze.) and 'Empire' zoysiagrass ( Steud). The research was conducted in Citra, FL, from 2005 through 2007. Nitrogen (N) was applied at annual rates of 32, 64, 128, and 196 kg ha⁻¹ in 2005, and at 49, 196, 343, or 490 kg ha⁻¹ in 2006 and 2007. Irrigation treatments consisted of 1.3 cm applied twice weekly or 2.6 cm applied once weekly. In general, NO₃-N leaching was greater from zoysiagrass. In 2007, annual NO₃-N leached varied due to the interaction of NR, IR, and grass. There was little association between NR and increased NO₃-N leaching in St. Augustinegrass in any year. While St. Augustinegrass had no differences in NO₃-N leached within NR due to IR, there were some differences in NO₃-N leached from zoysiagrass at some N levels, with greater NO₃-N leached from the more frequent irrigation regime. Turf quality (TQ) was generally above an acceptable level in St. Augustinegrass at all but the lowest NRs and at all NRs in zoysiagrass with the exception of the spring fertilizer cycle (SFC) in 2007, when high NR treatments resulted in disease. Maintenance of a healthy turfgrass cover is an important strategy for reducing potential nutrient movement from fertilizer application. The current recommended rates for St. Augustinegrass provide good turf cover and health, and result in minimal NO₃-N leaching. Zoysiagrass N rates may need to be revised downward to reduce disease, improve turf cover, and reduce NO₃-N leaching.