Responses of Zoysia matrella growth, soil mineral nitrogen, and nitrogen balance to different levels of irrigation and mowing

The major landscape type in urban green space ecosystems, urban turfgrass is strongly disturbed by anthropogenic management practices. In this study, three irrigation levels (I₁: 4.00 L·m⁻²; I₂: 5.71 L·m⁻²; I₃: 7.43 L·m⁻²) and three mowing levels (M₁: no mowing; M₂: 2 cm stubble; M₃: 6 cm stubble) were simulated to investigate the effects of different irrigation and mowing levels on Zoysia matrella (a warm season turfgrass) growth, soil mineral nitrogen, and the apparent soil nitrogen balance. The results showed that the above-ground biomass (AGB) of turfgrass in M₂ treatment was significantly lower than those in M₁ and M₃ treatments under the same irrigation level. Meanwhile, the nitrogen concentration of above-ground or below-ground part of turfgrass in M₂ treatment was significantly higher than that in M₁ treatment. At the end of turfgrass growth, soil mineral nitrogen (N_min) concentration decreased by 0.6% to 54.1% in the M₂ treatment compared to the M₁ and M₃ treatments under the same irrigation level. Ammonium nitrogen (NH₄⁺-N) was the main form of leachate N in all treatments, and N_min leaching only accounted for 0.4%～1.3% of the total nitrogen output. More nitrogen surplus was observed in the M₂ treatment compared to the M₃ treatment under the same irrigation level (P < 0.05). Meanwhile, more balanced nitrogen occurred in the M₃ treatment at the higher irrigation level. In summary, heavy mowing (M₂ treatment) significantly inhibited turfgrass growth and elevated the risk of nitrogen loss, but increased turfgrass nitrogen uptake. Therefore, based on our study findings, it can be suggested that irrigating slightly more water than the conventional level ranging from 5.71 to 7.43 L·m⁻² in combination with mowing moderately and keeping the stubble height at 6 cm are favorable to ensure suitable growth conditions of turfgrass and to maintain the balance of soil nitrogen and improve nitrogen utilization efficiency.