Onion growers in New Mexico often withhold irrigation for overwintered onion varieties during the months of December and January. This study was initiated to determine if this deficit irrigation program is detrimental to onion bulb quality. Twelve short- and intermediate-day onion cultivars, which differed in their maturity, were seeded in Sept. 2004 in Las Cruces, N.M. Once plants were established, 12 plots of each cultivar were not irrigated during the months of December and January (dry treatment), while the same number of plots was irrigated during these months (wet treatment). Once a plot had 80% of the plants with tops down, all bulbs were harvested, cured, and data on date of harvesting, bulb diameter, bulb height, firmness rating, number of centers, scale number, and scale thickness of first and third fleshy layers were collected. For most of the bulb traits measured, there was no difference between the two irrigation treatments for the cultivars tested. For the earliest-maturing cultivars, bulbs grown in the dry treatment had on average more fleshy scale layers than the bulbs grown in the wet treatment. For later-maturing cultivars, bulbs grown in the dry treatment had more growing points (centers) per bulb than the bulbs grown in the wet treatment. For the latest-maturing cultivars, average fleshy scale layer thickness was greater for bulbs grown in the dry treatment. From this work, a winter deficit irrigation program appears to be detrimental to the percentage of single-center bulbs for later-maturing, autumn-sown onion cultivars.
Jagtar Singh and Christopher S. Cramer
Geno A. Picchioni, Jagtar Singh, John G. Mexal, and Ryan M. Goss
The authors used a simple procedure to teach how to generate evapotranspiration (ET) data for both 1- and 5-gal pots of the xeric shrub apache plume (Fallugia paradoxa) and the mesic vine japanese honeysuckle (Lonicera japonica ‘Halliana’). In-class instruction and assigned reading prepared students for collecting data over a 22-day period (12 Apr. to 3 May), processing data on an electronic spreadsheet, accessing the Internet to acquire reference plant ET data, calculating a crop coefficient (Kc), preparing graphs, organizing a digital presentation, and presenting the findings to commercial nursery participants and instructors. When averaged across days and pot sizes, ET of japanese honeysuckle was 1.22 cm·d−1, whereas ET of apache plume was only 0.80 cm·d−1. This finding supported the students' hypothesis that a nursery block of potted mesic vines would use more water than a nursery block of potted xeric shrubs per unit of ground area. Commercial nursery participants adopted the ET monitoring technique after viewing the student presentation, indicating effective transfer of information by the students. The simple, inexpensive, 3-week exercise furthered the students' horticulture knowledge and comprehension while allowing for a collaborative effort with the local nursery industry.