Abstract
The objective of this two-year field study was to assess the influence of stand establishment methods (direct seeding or transplanting) on root growth dynamics, shoot morphology, leaf physiology, yield, and quality of globe artichoke (Cynara cardunculus). Three artichoke cultivars were evaluated, ‘Green Globe Improved’ (GGI), ‘Imperial Star’ (IS), and ‘Romolo’ (ROM). Plants established with the transplanting method had higher mean root length intensity (La), root length, and root surface area as compared to plants established by direct seeding. The topsoil (0–20 cm) had on average higher La, root length, and root surface area than deeper soil profiles. Transplanted plants had higher plant shoot width and leaf area index (LAI) chlorophyll content index (SPAD) than direct seeded plants at the vegetative stage in 2015. The improvement of root and shoot growth in transplants (compared to direct seeding) also resulted in higher (p < 0.05) marketable yield (21.1 vs. 19.9 ton ha−1 in 2015 and 18.3 vs. 13.7 ton ha−1 in 2016). Additionally, 46–50% of the total yield occurred during the first 30 days of harvest in the transplanting method compared to 13–38% for direct seeding. No significant differences were found between planting methods or cultivars in leaf-level gas exchange (photosynthesis, stomatal conductance, and transpiration) and cynarin concentration in the marketable heads. Although chlorogenic acid was similar in both establishment methods in 2015, direct seeding had higher concentration in 2016. Comparing cultivars, GGI had higher root length, surface area, root volume, and earlier and higher marketable yield than ROM. However, ROM had higher mean root length intensity (La; total root length per specific area in soil profile) than GGI in both growing seasons. This study showed significant and consistent improvements in root and shoot traits, and yield for transplants as compared to direct seeded plants.
Highlights
Farming systems, nitrogen management, cultivar selection, and planting methods such as direct seeding and transplanting are cultural strategies that greatly influence root and shoot growth, yield, and fruit quality in high-value vegetable crops [1,2,3,4]
Root length values for direct seeded plants never exceeded those of transplants across months and over the study period 2015–2016
While direct seeded plants develop a vertical strong taproot in non-compacted soils, transplanted seedlings develop a distinctive root system with typically more basal roots derived from the root–hypocotyl transition zone, which is caused by the early modification of the taproot in the containers; these changes lead to more uniform growth and higher crop yields compared to direct seeding [9,15,26,27]
Summary
Nitrogen management, cultivar selection, and planting methods such as direct seeding and transplanting are cultural strategies that greatly influence root and shoot growth, yield, and fruit quality in high-value vegetable crops [1,2,3,4]. In bell pepper (Capsicum annuum), earlier studies comparing direct seeding with containerized transplants produced in nurseries showed significant effects on growth (leaf area and shoot weight) and developmental stages in the field [5]. Artichoke (Cynara cardunculus) fields established with the transplanting method typically have less weed pressure and disease problems and higher yield and head uniformity as compared to direct seeding [9]. Transplant quality can be improved during the nursery stage by optimizing the nitrogen nutrition of the growing substrate in the tray cells, a practice that was shown to mitigate the transplanting shock during stand establishment of globe artichoke [3]
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