Irrigation Thresholds for Onion, Celery and Spinach in Histosols.

Identifying critical soil water potential is a key step for saving water and optimize crop productivity for vegetable production in muck soils. This study aimed at determining the optimal soil water potential for irrigating onion, celery, and spinach crops in a Histosol. Onion and celery were subjected to three irrigation treatments scheduled when tensiometers readings at 0.2 m depth reached -10 and −20 kPa (onion) and −30 and −50 kPa and −15 and −30 kPa (celery), compared to drier control treatments for both crops. For spinach, two irrigation treatments (−10 and −20 kPa) and a control (drier) were tested. Optimal onion marketable yields and jumbo size were obtained from irrigation at potentials above −20 kPa at the bulbing stage. Celery recorded best yields with the −15 and −30 kPa treatments relative to the drier control. The highest spinach germination rate and yield were obtained at −10 kPa relative to drier conditions. Reliable estimates of the optimal thresholds were consistent with calculations performed using a simple analytical solution to Richards’ equation and soil characteristics.