Nitrogen budgets of urban lawns under three different management regimes in southern California

Abstract

We constructed nitrogen (N) budgets for the lawns of three simulated residences built to test the environmental impacts of three different residential landscape designs in southern California. The three designs included: a “Typical” lawn planted with cool season tall fescue (Schedonorus phoenix), fertilized at the recommended rate for this species (192 kg−1 ha−1 year−1) and irrigated with an automatic timer; a design intended to lower N and water requirements (“Low Input”) with the warm season seashore paspalum (Paspalum vaginatum) fertilized at 123 kg−1 ha−1 year−1 and irrigated with a soil moisture-based system; and a design incorporating local best practices (“Low Impact” lawn) that included the native sedge species Carex, fertilized at 48 kg−1 ha−1 year−1 and irrigated by a weather station-based system. Plant N uptake accounted for 33.2 ± 0.5 (tall fescue), 53.7 ± 0.7 (seashore paspalum), and 12.2 ± 1.3 % (Carex) of annual N inputs, while estimated N retention in soil was relatively large and similar in the three lawns (41–46 %). At lower N and water inputs than Typical, Low Input showed the highest annual clipping yield and N uptake, although it also had higher denitrification rates. Leaching inorganic N losses remained low even from the Typical lawn (2 %), while gaseous N losses were highly variable. The Low Input lawn was most efficient in retaining N with relatively low water and N costs, although its fertilization rates could be further reduced to lower gaseous N losses. Our results suggest that the choice of a warm-season, C4 turf species with reduced rates of irrigation and fertilization is effective in this semi-arid region to maintain high productivity and N retention in plants and soils at low N and water inputs.