Large intra-annual N fluxes between soil and plant pools in a turfgrass lawn

Background/Question/Methods

Turfgrass lawns represent a large fraction of urbanized land cover in the United States. Given high (3-5%) biomass N concentrations and net primary production that is comparable to other temperate ecosystems, it is likely that lawns will play a significant role in urban N dynamics.  In order to gauge the magnitude of N fluxes in a standard home lawn turfgrass system, we measured biomass and soil N pools in a tall fescue lawn (Festuca arundinaceaSchreb.) over most of two growing seasons, while applying management treatments to simulate a range of reported homeowner practices.

Results/Conclusions

While there was no net change in soil or biomass N pools on an annual basis, we observed significant intra-annual variation. Biomass pools increased by ~200 kg N ha^-1 in the spring, then decreased through the summer and fall, while the soil pool decreased by ~300 kg N ha^-1 in the spring, then increased through the summer and fall.  Management practices (mowing height, irrigation, and fertilization level) had significant effects on the magnitude of this variation, but did not change the general pattern.  These results appear to show a large flux of N from the soil to plant biomass in the spring, followed by a gradual return of N from plant biomass to the soil.