Drip Irrigation Management Affects Celery Yield and Quality

Trials in nine commercial celery (Apium graveolens L.) fields were conducted between 1997–99 to evaluate grower drip irrigation management practices and their effects on yield and quality. Surface drip irrigation tapes with flow rates higher and lower than the grower-installed tapes were spliced into the field system; as the cooperating growers irrigated and applied N fertigation according to their routine practices these drip tapes delivered either more or less water and N than the field drip system. Total grower water application during the drip-irrigated portion of the season ranged from 85% to 414% of seasonal reference evapotranspiration (ETo). Water volume per irrigation varied among fields from 1.8 to 3.8 cm, with irrigation frequency varying from an average of every other day to once a week. Grower management of drip irrigation was not consistently successful in maintaining soil water tension (SWT) in a desirable range. SWT was often below –30 kPa, and in some cases below –70 kPa. These transient stresses were more often a result of inappropriate irrigation frequency than applied water volume. In four of the fields plots receiving less water than that delivered by the field system produced equivalent marketable yield and quality, indicating a significant potential for water savings. An economically important incidence of petiole pithiness (collapse of parenchyma tissue) was observed in four fields. Infrequent irrigation under high ETo summer conditions, rather than irrigation volume applied, appeared to be the major factor in pith development. N fertigation amount and crop N status appeared to be unrelated to pithiness severity. We conclude that celery drip irrigation management could be substantially improved by maintaining a closer proportionality between irrigation and crop evapotranspiration (ETc), increasing irrigation frequency, and reducing volume per irrigation. field system. As the cooperating growers managed the fields according to their routine practices these plots received either more or less water (and fertigated N) than the plots irrigated by the field system. Among the various drip tapes used emitter spacing ranged from 20–40 cm, with emitter output ranging from ≈0.5–1.0 L·h. Three to five irrigation rates were evaluated in each field. Experimental designs were randomized complete blocks with four replications, with individual plots 4 beds wide × 7.5 m long. The plots were arranged sequentially along the same four beds. All data were collected from the middle beds. No precipitation was received during the drip-irrigated portion of the season except in fields 2 and 9, which received 1.8 and 1.1 cm, respectively, in the week before harvest. Irrigation volume applied in the experimental area was recorded by an in-line water meter on each of the two middle beds of the test plots. The flow from three individual emitters in each plot was periodically captured to document the relative flow rates in the various treatments. A tensiometer (Irrometer Co., Riverside Calif.) was installed 25–30 cm deep in the plant row in each plot to document soil water tension prior to each irrigation. Computerized weather stations from the California Irrigation Management Information System network (CIMIS, Snyder and Pruitt, 1992) provided daily reference evapotranspiration (ETo, modified Penman) values for each field. Plant canopy development (percentage of ground area covered) was visually estimated in each field several times in the growing season. Cooperating growers were asked to provide details of their N applications. Plant N status was evaluated at midseason by petiole sampling and at harvest by sampling the marketable portion of whole plants. Tissue samples were oven-dried and ground. Petiole tissue was extracted in 2% acetic acid and analyzed for NO3-N concentration by the method of Carlson et al. (1990). Total N concentration in the harvest samples was determined by a combustion technique (CarloErba 1500; Fisons Instruments, Beverly, Mass.). The plots were harvested at commercial maturity. Data collected included mean total and marketable mass, and incidence of petiole pithiness. Plants having two or more marketable petioles showing parenchyma breakdown were considered to have an objectionable level of the disorder; the percentage of plants showing this level of the disorder was recorded. The significance of irrigation treatment effects on celery yield and incidence of pithiness was determined using orthogonal contrasts to compare individual irrigation treatments with the field irrigation rate.