Second-Year Effects of Biochar, Biosolids, and Greenwaste on Tall Fescue Under Deficit Irrigation: Part II

Soil amendments are widely applied for water conservation in urban turfgrass, yet whether establishment-phase benefits persist into a mature-stand remains unclear. This study evaluated biochar, biosolids, and greenwaste on tall fescue (Schedonorus arundinaceus) over a 108-day mature-stand trial under deficit (50% ET0) and moderate (85% ET0) irrigation, both below full replacement. Canopy performance was assessed by visual quality and NDVI, with van Genuchten soil-water retention modeling. Unlike the establishment-phase advantages reported for the organic amendments in Part I, the second-year results reversed sharply: moderate biochar (12.36 t ha−1) was most hydraulically stable, holding the highest plant-available water (PAW ≈ 0.18 cm3 cm−3, above the control and organic amendments) and the most stable canopy. High-rate biochar (24.71 t ha−1) underperformed the control under deficit irrigation, indicating constraints beyond water retention at the highest rate. Greenwaste and biosolids raised volumetric water content but provided lower PAW than moderate biochar. For greenwaste, a reduced field capacity offset this; for biosolids, an elevated permanent wilting point limited the extractable fraction. Biosolids failed to maintain acceptable quality even under the 85% ET0. Because first-year success does not guarantee mature-stand resilience, amendment stability and rate optimization, rather than application volume, emerge as long-term management priorities under water-limited conditions.