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The increasing water shortage in the arid and semiarid western USA requires use of recycled wastewater (RWW) when possible. Recycled wastewater has become a common water source for irrigating golf courses and urban landscapes, creating the need to study the effects of RWW irrigation on soil chemical properties. We compiled soil test data from fairways of 10 golf courses that were near metropolitan Denver and Fort Collins, CO. Among these courses, five had been irrigated exclusively with domestic RWW [electrical conductivity (EC) = 0.84 dS m−1] for 4, 13, 14, 19, and 33 yr, respectively. The other five with similar turf species, age ranges, and soil textures had used surface water (EC = 0.23 dS m−1) for irrigation. Our results indicated that soils (sampled to 11.4 cm) from fairways with RWW irrigation exhibited 0.3 units of higher pH and 200, 40, and 30% higher concentrations of extractable Na, B, and P, respectively. Compared with sites irrigated with surface water, sites irrigated with RWW exhibited 187% higher EC and 481% higher sodium adsorption ratio (SAR). Comparison of soil chemical properties before and 4 or 5 yr after RWW irrigation on two golf courses also revealed the following findings: (i) 89 to 95% increase in Na content; (ii) 28 to 50% increase in B content; and (iii) 89 to 117% increase in P content at the surface depth. Regular monitoring of site‐specific water and soil and appropriate management are needed to mitigate the negative impacts of sodium and salts accumulations.

Experiments to document the long-term effects of clipping management on N requirements, soil organic carbon (SOC), and soil organic nitrogen (SON) are difficult and costly and therefore few. The CENTURY ecosystem model offers an opportunity to study long-term effects of turfgrass clipping management on biomass production, N requirements, SOC and SON, and N leaching through computer simulation. In this study, the model was verified by comparing CENTURY-predicted Kentucky bluegrass (Poa pratensis L.) clipping yields with field-measured clipping yields. Long-term simulations were run for Kentucky bluegrass grown under home lawn conditions on a clay loam soil in Colorado. The model predicted that compared with clipping-removed management, returning clippings for 10 to 50 yr would increase soil C sequestration by 11 to 25% and nitrogen sequestration by 12 to 28% under a high (150 kg N ha(-1) yr(-1) nitrogen (N) fertilization regime, and increase soil carbon sequestration by 11 to 59% and N sequestration by 14 to 78% under a low (75 kg N ha(-1) yr(-1)) N fertilization regime. The CENTURY model was further used as a management supporting system to generate optimal N fertilization rates as a function of turfgrass age. Returning grass clippings to the turf-soil ecosystem can reduce N requirements by 25% from 1 to 10 yr after turf establishment, by 33% 11 to 25 yr after establishment, by 50% 25 to 50 yr after establishment, and by 60% thereafter. The CENTURY model shows potential for use as a decision-supporting tool for maintaining turf quality and minimizing negative environmental impacts.

To predict the best management practices for Kentucky bluegrass (Poa pratensis L.) lawns in Colorado, the DAYCENT ecosystem model was parameterized and applied on a turfgrass ecosystem. In this study, field‐measured data on clipping yields, leaf N content, evapotranspiration (ET), deep percolation, nitrate leaching, and soil temperature from a 3‐yr lysimeter study were used for parameterization and validation. The simulation result for clipping yield was improved compared to the monthly time step CENTURY ecosystem model, with correlation coefficient (r) increased from −0.32 to 0.74. The prediction of ET and deep percolation was acceptable for the 3 yr. The long‐term irrigation and fertilization effects on Kentucky bluegrass biomass and soil C and N were also examined. We predicted a 50% reduction in the annual net production as irrigation decreases from 100% potential evapotranspiration (PET) to 60% PET in this semiarid region. The simulation result suggests that the annual fertilization rates should be gradually reduced for both moderately and highly managed lawns with increasing age of the turfgrass stand.

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