Deficit Irrigation and Fertility Effects on NO3-N Exports from St. Augustinegrass.

Proper management of turfgrass systems is critical for reducing the risk of nutrient loss and protecting urban surface waters. In the southern United States, irrigation can be the most significant management practice regulating the biogeochemical and hydrological cycles of turfgrass systems. A turfgrass runoff research facility was used to assess the effects of deficit irrigation and fertilizer applications on turfgrass canopy cover and nitrate-N (NO-N) exports in runoff from St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] turf over a 2-yr period. Treatments were arranged as a randomized complete block design having eight combinations of irrigation (100, 75, or 50% of estimated turfgrass water requirements) and fertility level (0, 88, and 176 kg N ha yr). Runoff from 31 rainfall events and one irrigation excess event were used to estimate annual and seasonal NO-N exports. The majority of annual NO-N exports occurred during the late winter and spring. Deficit irrigation reduced summer and early autumn runoff volumes. Lower summer and autumn runoff volumes (from deficit irrigation) coincided with reduced NO-N exports from runoff during Year 1. Deficit irrigation combined with fertilizer applications increased runoff [NO-N] in Year 2, suggesting that the previous year's export reduction contributed to higher N accumulation in the system and thus a higher N loss potential. These findings suggest that deficit irrigation can be a tool for reducing seasonal nutrient exports from St. Augustinegrass lawns so long as fertilizer inputs are moderate.