International Water & Irrigation

40 Materials and Methods Plant culture and treatments. The study was conducted in the agricultural research department of a University in Mississippi, the United States. One-year-old liners (grown in 4-inch trays) of azalea ‘Chiffon’ were potted in pine bark substrate into two types of I-gallon containers, one of black plastic and the other a biodegradable container (biocontainer) made from a mix of recycled paper. Each azalea chiffon plant was fertilized with 250 mL of N-free fertilizer plus 0, 5, 10, 15, or 20 mM N from NH4NO3 applied twice weekly from mid-April to mid-September Plants were irrigated either once per day at 8:00 AM or twice per day at 8:00 AM and 2:30 PM with the same total daily irrigation amount. Plants were irrigated to replace daily water loss plus 15% leaching fraction. Measurements and data collection. Plant height and widths (width I, the greatest width; width 2, perpendicular to width 1) were measured on each plant every two weeks. Plant growth index was calculated as the average of plant height, width I, and width 2. Three fully expanded new leaves were selected from each plant to measure their leaf SPAD reading using a chlorophyll meter on the same interval as plant height and widths. An average of the three readings from three leaves was calculated to represent SPAD of a specific plant. Plants were destructively harvested and separated into root, stem, and leaf structures, 32 weeks after transplanting. Dry weights and N analyses. All plant samples were cleaned free of debris and substrate using deionized water and oven dried at 60 °C to constant dry weight. Dry weight of each sample was recorded. Total plant N content was calculated by summing N content in leaf, stem, and root. Average plant N concentration was calculated by dividing total plant dry weight by total plant N content. Results Plant growth. Growth of azalea transplants were uniform starting from 2 weeks after transplanting, with no significant difference in PGI or SP AD readings among all treatment combinations. By the time of destructive harvest in November, SP AD reading was affected by the main effect of N rate (P < 0.0001) and increased significantly with increasing N rate (from17.0 at 0 mM to 38.6 at 20 mMN), irrespective of irrigation frequency or container type (Table I). PGI was affected by irrigation frequency (P = 0.0107) and the interaction between N rate and container type (P < 0.0001) (Tables One and Three) . Plants irrigated once per day had 7.7% higher PGI (18.56) than those irrigated twice per day (17.35) averaged over all N rates and both container types (Table Three) . When grown in plastic containers, PGI of azalea plant increased significantly (from 12.07 to 19.27) with increasing N rates. When grown in biocontainers, PGI of azalea plant increased significantly (from 11.13 to 24.33) with increasing N rates, Dry weights (leaf, stem, root, or total plant dry weight) Biodegradable plant containers Azaria Chiffon plant in a plastic container One irrigation per day resulted in greater root growth and better flower production, although irrigation frequency did not affect plant N uptake