Elevated soil nitrogen pools after conversion of turfgrass to water-efficient residential landscapes

Abstract

As a result of uncertain resource availability and growing populations, city managers are implementing conservation plans that aim to provide services for people while reducing household resource use. For example, in the US, municipalities are incentivizing homeowners to replace their water-intensive turfgrass lawns with water-efficient landscapes consisting of interspersed drought-tolerant shrubs and trees with rock or mulch groundcover (e.g. xeriscapes, rain gardens, water-wise landscapes). While these strategies are likely to reduce water demand, the consequences for other ecosystem services are unclear. Previous studies in controlled, experimental landscapes have shown that conversion from turfgrass to shrubs may lead to high rates of nutrient leaching from soils. However, little is known about the longterm biogeochemical consequences of this increasingly common land cover change across diverse homeowner management practices. We explored the fate of soil nitrogen (N) across a chronosequence of land cover change from turfgrass to water-efficient landscapes in privately owned yards in metropolitan Phoenix, Arizona, in the arid US Southwest. Soil nitrate ( -NO 3 -N) pools were four times larger in water-efficient landscapes (25±4 kg -NO 3 -N/ha; 0-45 cm depth) compared to turfgrass lawns (6±7 kg -NO 3 -N/ha). Soil -NO 3 -N also varied significantly with time since landscape conversion; the largest pools occurred at 9-13 years after turfgrass removal and declined to levels comparable to turfgrass thereafter. Variation in soil -NO 3 -N with landscape age was strongly influenced by management practices related to soil water availability, including shrub cover, sub-surface plastic sheeting, and irrigation frequency. Our findings show that transitioning from turfgrass to water-efficient residential landscaping can lead to an accumulation of -NO 3 -N that may be lost from the plant rooting zone over time following irrigation or rainfall. These results have implications for best management practices to optimize the benefits of water-conserving landscapes while protecting water quality.

Increased soil moisture intensifies the impacts of forest-to-pasture conversion on methane emissions and methane-cycling communities in the Eastern Amazon

“…Sand, silt, and clay contents were determined by the hydrometer method and classified according to the United States Department of Agriculture textural classification system (USDA, 2019). The gravimetric moisture of each representative sample was determined in triplicate by its weighing before and after drying at 105 • C for 72h (Claessen, 1997); while the gravimetric field capacity (FC) was determined in triplicate as described by Heavenrich and Hall (2016) by its saturation and drainage undercover at room temperature, followed by its weighing before and after drying at 105 • C for 72h (Claessen, 1997).…”