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

As urban water scarcity intensifies, selecting soil amendments is critical for drought-stressed landscapes. This study evaluated biochar, biosolids, and greenwaste effects on canopy quality, soil moisture, nitrogen dynamics, and root architecture in tall fescue (Schedonorus arundinaceus) in the post-establishment year. Eight amendment treatments were assessed under two irrigation regimes (50% and 85% of reference evapotranspiration [ET0]) in a split-split-plot arrangement with four replications. No treatment maintained acceptable visual quality (VQ ≥ 6.0) under the 50% ET0 deficit. A 10 cm greenwaste layer raised soil moisture up to 27% above the control but produced the lowest mineral nitrogen concentrations at both depths, and this advantage did not translate into improved canopy performance. High-rate biochar (24.71 t ha−1) maintained superior NDVI during peak stress, whereas biosolids generated the highest soil nitrogen (Total N up to 9.62 mg kg−1) but restricted root length, surface area, and branching. Because no amendment optimizes moisture, nitrogen, and rooting together, selection should target the limiting factor: pair greenwaste with nitrogen, use biochar where nitrogen is limited, and reserve biosolids for nitrogen-poor, non-root-limited sites. Under a 41% irrigation reduction, no amendment sustained acceptable quality, so managers should temper expectations or choose more drought-tolerant species rather than soil management alone.