Nitrogen leaching and groundwater recharge of alternative lawn conversions in subtropical climates

Climate change, recurrent droughts, and increasing urban water demands have limited water availability in urban landscapes. Water quantity challenges have led to irrigation restrictions and turfgrass removal programs. An experiment was conducted at the University of Florida, West Florida Research and Education Center, Jay, FL, to evaluate the effect of turfgrass conversion to other landscape types on nutrient leaching and groundwater recharge. In April 2021, all surface vegetation was removed from existing turfgrass plots using a sod harvester. Thereafter, plots were planted or covered with three landscape types: a pollinator landscape with flowering forbs (Mimosa sp., Coreopsis sp., and Phyla sp.) + turfgrass (Eremochloa ophiuroides); a nitrogen (N)-efficient lawn (Arachis glabrata + Paspalum notatum); and a low-input landscape with unplanted woodchip mulch. Undisturbed turfgrass (E. ophiuroides) served as a control. For 2 years, leachate samples were collected weekly from previously installed 168-L drainage lysimeters for NO3-N and NH4-N load determination. Temporal changes in landscape composition, groundwater recharge, water use, and soil bulk density were also quantified. While the mulch leached 44.7 kg ha-1 NO3-N year-1, this landscape still offers positive attributes, including erosion protection and water conservation. Conversely, the pollinator landscape minimized nitrogen leaching (8.3 kg ha-1 NO3-N year-1) due to their relatively greater water use rates (3.56 mm day-1). The turfgrass and nitrogen-efficient lawn returned similar to 35% of the water inputs as groundwater recharge while maintaining relatively low nitrogen leaching (3.6 and 2.7 kg ha-1 NO3-N year-1, respectively), making these landscapes efficient for protecting both water quality and quantity. Rapid conversion of turfgrass to a nitrogen-efficient lawn or pollinator landscape did not result in N leaching. Turfgrass removal and replacement with unplanted woodchip mulch resulted in N leaching. Turfgrass and nitrogen-efficient lawns provided the best groundwater recharge services. Climate change, recurrent droughts, and increasing urban water demands have limited water availability in urban landscapes. This has led to irrigation restrictions and the implementation of turfgrass removal programs. This study aimed to assess the impact of turfgrass removal and conversion to alternative landscapes, including a pollinator-friendly landscape with flowering forbs (frog fruit, sunshine mimosa, and coreopsis), a nitrogen-efficient lawn (legumes + turfgrass), and a low-input landscape with unplanted woodchip mulch. The conversion to the nitrogen-efficient lawn or pollinator landscape did not produce nitrogen pollution in groundwater. Conversely, replacing turfgrass with unplanted woodchip mulch led to nitrogen leaching due to the absence of plant roots to assimilate nutrients and water. The turfgrass and nitrogen-efficient lawn returned similar to 35% of water inputs as groundwater recharge while having low nitrogen leaching, making them efficient at protecting water quality and quantity.