Irrigation Method and Fertilizer Concentration Differentially Alter Growth of Vegetable Transplants

Abstract

In the United States, overhead irrigation is common to apply water and dissolved nutrients to vegetable transplants during greenhouse production. Overhead irrigation allows for the control of salt accumulation in the growing medium because excess water can leach salts out of the container. Alternatively, subirrigation saves labor and improves water use efficiency, but soluble salts can accumulate in the upper profile of the containers. Consequently different sets of fertilizer and electrical conductivity (EC) guidelines are required for overhead and subirrigation systems. The objective of this project was to determine the influence of fertilizer concentration and irrigation method (subirrigation vs. overhead irrigation) on the growth of several vegetable transplant crops intended for retail sale. Seedlings of collards (Brassica oleracea var. acephala ‘Vates’), kale (B. oleracea var. acephala ‘Nagoya Mix’), lettuce (Lactuca sativa ‘Buttercrunch’), pepper (Capsicum annuum ‘Sweet Banana’), and tomato (Solanum lycopersicum ‘Sweet 100’) were transplanted into 4-inch-diameter containers and grown in a greenhouse for 4 weeks. Irrigation was provided via ebb and flow benches (subirrigation) or hand-watering (overhead irrigation). Plants received a complete fertilizer solution provided at a concentration of 50, 100, 200, 350, and 500 mg·L−1 nitrogen (N). The treatments resulting in maximum shoot dry weight (DW) for overhead irrigated plants were 100 mg·L−1 N for pepper, 200 mg· L−1 N for tomato, and 350 mg·L−1 N for collards, kale, and lettuce. Irrigation method and fertilizer treatment significantly affected fresh weight (FW) and DW for kale, lettuce, and pepper. For kale and lettuce, regression analysis indicated that maximum DW was reached at a lower fertilizer concentration with overhead irrigation than subirrigation. The treatments resulting in maximum DW for subirrigated plants were 200 mg·L−1 N for kale, lettuce, pepper, and tomato and 350 mg·L−1 N for collards. Reducing fertilizer concentration was an effective method for controlling plant height for all crops we examined except for ‘Sweet Banana’ pepper. However, in many cases height control via nutritional limitation comes at substantial expense to other growth parameters. Our results suggest that, in some cases, fertilizer concentration guidelines for overhead irrigation can be reduced when growing vegetable transplants with subirrigation due to reduced leaching of nutrients and greater potential for accumulation of fertilizer salts.