Estimation of lily crop coefficient at different phenological development stages in a greenhouse

Determining the phenological growth stages is crucial for estimating crop growth and development. Stage-specific crop coefficient (K_c) values, derived from phenological stages, are essential for optimizing irrigation scheduling in lily cultivation. This study quantified the crop water requirements (CWR) of lilies by estimating evapotranspiration (ET) at different growth stages. Using a modified Biologische Bundesanstalt, Bundessortenamt und CHemische Industrie (BBCH) scale, six principal stages were defined: germination/sprouting (stage 0), stem elongation and leaf development (stage 1), inflorescence emergence (stage 5), flowering (stage 6), bulb development (stage 7), and senescence (stage 9). Growing degree days (GDD) consistently predicted bud visible and flowering stages across different conditions. Changes in bulb dry weight and size illustrated the source-sink transition throughout the growth cycle of lilies. Reference evapotranspiration (ET_o) was estimated using the FAO-56 Penman–Monteith equation, a widely used method for estimating ET_o, and calibrated for an experimental greenhouse to improve accuracy. Crop evapotranspiration (ET_c), defined as the actual evapotranspiration of the lily crop, varied across growth stages, with daily means of 0.93, 1.95, 2.11, 1.88, and 1.80 mm·d⁻¹ in stages 0, 1, 5, 6, and 7–9, respectively. These values indicate that water minimal water use at germination, peak consumption during inflorescence emergence and flowering, and a decline during bulb development and senescence. The corresponding mean K_c values were 0.7, 1.0, 1.1, 1.1, and 0.8. These findings highlight the distinct water use pattern of lilies and provide an approach for optimizing irrigation efficiency in greenhouse cultivation by integrating phenology-based K_c values into scheduling.