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  • Author or Editor: Yahia A. Othman x
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The impact of nitrogen application on the growth of olive trees has been well studied. However, little is known about the role of levels and forms of N on the development of roots and physiological traits during establishment of young trees. The objective of this 2-year study was to evaluate the influence of N source and level on shoot morphology (tree height, stem diameter, and branch number) and physiology [leaf area and fresh weight, photosynthesis (Pn), transpiration (E), and stomatal conductance (g s)], root components (length, diameter, surface area, and fork number) and N content of young olive (Olea europaea cv. Arbequina) cuttings. Three-month-old olive cuttings were planted in 15-L pots filled with a growing substrate composed of peatmoss + bark + sand (2:1:1/by volume) and placed in a screen house. Two N levels, 2.8 and 5.6 g/tree, and control (0 N) and four N sources, calcium nitrate (CN, 12%N, 17%Ca+2), ammonium nitrate (AN, 35%N), urea (46%N), and the slow-release Osmocote (OSC, 18%N, 6%P, 12%K) were evaluated. Effects of low– (2.8 g/tree) and high N (5.6 g/tree) levels on shoot components (plant height, diameter, branch number, leaf area, and fresh weight) and gas exchange (Pn, g s and E) were similar implying that the low rate of N was adequate for the establishment of young olive cuttings. Nitrogen sources, particularly AN and CN had significant effects on shoot and root morphology, physiology, and leaf and root N concentration. In fact, AN and CN were the best fertilizer sources for olive transplants in term of root and shoot growth. Overall, 2.8 g/tree N level and AN or CN sources were the best treatments for newly established olive ‘Arbequina’ trees. Root components treated with high N rate (5.6 g/tree N) using the slow-release fertilizer (OSC) was similar to those treated with the low AN rate (2.8 g/tree N). Therefore, for nursery containerized olive trees of ‘Arbequina’ or other cultivars with comparable growth rates, we recommend to apply the CN or AN source at 2.8 g/tree N or the controlled-released fertilizer OSC at 5.6 g/tree N.

Free access

Polyethylene mulch is widely used for vegetable production in the United States as a tool to conserve water, control weeds, and produce earlier and cleaner products (i.e., less attached soil). However, the increasing labor costs for mulch removal and disposal after harvest and soil environmental pollution are major concerns. The objective of this study was to assess fruit yield and quality, mulch deterioration, soil microbial activity, and nutrient changes in ‘Stargazer’ watermelon (Citrullus lanatus) grown with degradable plastic mulch. The deterioration rates of degradable mulch were 7%, 37%, 57%, and 92% after 120, 210, 300, and 365 days, respectively, of placing the mulch in the field. However, the extra difference in using degradable mulch was calculated as $58.6/acre (polyethylene $600.9/acre vs. degradable $659.5/acre), including all costs associated with laying and disposing. One year after placing mulch in the field, the nitrate content and total and active fungi numerically increased (P = 0.08) in soils with the degradable mulch compared with polyethylene mulch. However, there were no statistical differences in soil phosphorus, potassium, organic carbon, and total and active bacteria. Extra-large fruit size yield (category >24.0 lb) from the polyethylene mulch treatment was higher than that from degradable mulch, whereas the 18.0- to 24.0-lb category was lower than that with degradable mulch. However, total yield and total soluble solids from both mulches were statistically similar. Considering the complete deterioration (less waste), mulch removal cost (not required), microbial associations (higher fungi abundance and activity), and similar yield and fruit quality of degradable mulch compared with polyethylene, the implementation of degradable mulches in commercial watermelon field practices is promising.

Open Access

Soilless substrates enhance growing environment, nutrient content, and water quality in the growing medium. The objective of this study was to assess the influence of substrate particle size on growth and flower quality (flower number and length per plant) of two asiatic hybrid lily (Lilium ×elegans) cultivars Fangio and Ercolano. Plants were grown in 12-L pot under greenhouse conditions. Five grades of particle-size substrate, consisting of granulated volcanic material (tuff) were used as treatments. These sizes were 0 to 2, 0 to 4, 0 to 8, 2 to 4, and 4 to 8 mm. Fertigation was applied daily. Plant morphology, physiology, and flower quality were determined during flowering stage. Treatments of 2 to 4- and 4 to 8-mm tuff had lower water holding capacity (WHC), bulk density, electrical conductivity (EC), and pH compared with 0 to 2- and 0 to 4-mm tuff. In addition, plant height, leaf area, and flower quality of ‘Fangio’ were higher compared with ‘Ercolano’. Chlorophyll content and fluorescence were similar among all treatments. Leaf fresh weight, leaf area, shoot dry weight, root dry weight, and flower quality were higher in sizes of 0 to 4-, 2 to 4-, and 4 to 8-mm than 0 to 2-mm tuff, especially those from ‘Fangio’. The 0 to 4-mm substrate had an optimal and consistent flower quality results in both cultivars when compared with other tuff sizes. Overall, the results presented here suggest that using 0 to 4-mm tuff substrate holds promise for improving growth and flower quality of asiatic hybrid lily grown under soilless culture.

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