an additional 150 lb/acre N for dry bulb production ( Boyhan et al., 2001a ). The total N requirement of 280 lb/acre is the highest for any vegetable in Georgia, which might be reduced with direct-seeded onions ( Kissel, 2003 ). Furthermore, the Texas
George E. Boyhan, Juan Carlos Diaz-Perez, Chris Hopkins, Reid L. Torrance, and C. Randy Hill
George E. Boyhan, Juan Carlos Diaz-Perez, Reid L. Torrance, Ronald H. Blackley Jr., and C. Randell Hill
The majority of Vidalia onions are produced as a transplanted crop. Seeding in high density plantings in September is followed 8 to 10 weeks later by transplanting to final spacing. This practice is labor intensive and expensive. Direct seeding would save on labor, cost, and time. Traditionally, transplanting has been done because of better winter survival, more uniform stands, and better irrigation management during seedling emergence. Beginning 5 years ago, we began evaluating direct seeding onions. Initially, seedstems (bolting) and lack of uniform stand establishment were the main problems. Sowing in September resulted in almost 100% seedstems and using a belt planter with raw seed resulted in poor singulation for uniform stand establishment. Mid-October ultimately proved to be the best time for sowing Vidalia onion seed. Earlier sowing resulted in more seedstems and later planting did not give the plants sufficient time to grow resulting in later stand loss during cold winter temperatures. Using polymer coated seed and a precision vacuum planter resulted in uniform, even stand establishment. Fertilizer requirements are almost half with direct seeded onions compared to transplanted onions with a reduction in the need for fungicides and herbicides. We have established direct seeded onions both with drip irrigation and overhead irrigation. There was concern that center-pivot irrigation would not be able to sufficiently irrigate fields during seedling establishment with the frequent hot fall days we experience. Since this work was initiated several growers have successfully produced direct seeded onions under center-pivot systems. Direct seeding Vidalia onions requires attention to detail because there is only one opportunity to get it right. Timing is also critical particularly with planting date and herbicide application.
Martin Makgose Maboko and Christian Phillipus Du Plooy
Direct seeding of hydroponically grown tomatoes ( Solanum lycorpersicum ) is not a common practice in South Africa, and most growers use transplants. Seedlings for hydroponic production of fresh market tomatoes are commonly transplanted at 6 to 7
Brian A. Kahn, Niels O. Maness, Donna R. Chrz, and Lynda K. Carrier
. Basil is grown primarily from transplants ( Nurzyńska-Wierdak, 2002 ), but the crop can be established by direct seeding ( Davis, 1997 ; Simon, 1995 ). Producers are interested in direct seeding for basil stand establishment as a possible method to
Transplanting generally results in more rapid stand establishment than direct seeding for cucurbit crops. A 2-year field study was conducted to examine the pattern of rooting of watermelon [Citrullus lanatus (Thunb.) Matsum. & Nak.] following usage of different planting methods, and to determine subsequent effects on crop yield. Root length was assessed by obtaining soil cores three times per growing season to a depth of 75 cm. Transplanted watermelons generally had greater root length density in the upper 30 cm of soil 4 to 7 weeks after planting (WAP). However, by 11 to 12 WAP root distribution was similar over the entire 75 cm soil profile for the two planting methods. Total marketable yields were comparable for direct seeded and transplanted watermelons during 1995, but transplanted watermelon yield exceeded direct seeded yield by 40% in 1996. In both years, 90% to 100% of the marketable yield of transplanted watermelons was obtained at the first harvest, compared to 0% to 55% for direct seeded watermelons. These findings suggest that rapid root proliferation of transplanted watermelons may be an important factor in their earlier establishment and increased early yields as compared to direct seeded watermelons.
Daniel I. Leskovar
Pepper cv. `Jupiter' plants were field-grown from containerized transplants produced with either overhead (SPl) or sub-flotation (SP2) irrigation, or from direct seeding, in 3 years. Shoot and root growth were measured at frequent intervals. At planting, SPl transplants had larger basal root length and numbers than SP2 transplants. At the end of the growth period, basal, lateral, and taproot dry weights accounted for 81, 15, and 4% of the total for transplants, and 25, 57, and 18% of the total for direct-seeded plants. The coordination of growth (linear logarithm relationship) between root and shoot, changed after fruit set only in transplants. Over all seasons, transplants exhibited significantly higher yields than direct-seeded pepper plants.
Jesús Valencia and Donald M. May
An irrigation water study was conducted in the West side of Fresno County to evaluate the impact of recycled drainage water nitrogen and salinity content in the growth of direct seeded processing tomatoes to reduce nitrate-ground water pollution. Four canal water treatments (0.4 dS/m) received 0, 67.5, 101.2, and 168.7 kg of nitrogen per hectare and four saline water treatments (7.01 dS/m) received 0, 33.7, 67.5 and 135.0 kg nitrogen per hectare. All treatments were established with fresh canal water, and at first flower half of treatments were switched to saline water. The nitrogen content of water had an average of 283 ppm N-NO3 for the canal water and the drainage water contained 4489 ppm N-NO3. There was no significant yield differences between the irrigation methods and the two N-fertilizer sources applied to the tomatoes. However, drainage water produced a significant increase in fruit soluble solids (5.05 Av.) in comparison to canal water and synthetic fertilizer (4.3 Av.). The overall fruit quality and maturity was better in the drainage water treatments than it was in the fresh canal water with synthetic N-applied treatments.
J. Cavero, R. Gil Ortega, and C. Zaragoza
Pepper (Capsicum annuum L. `Piquillo de Lodosa') was seeded and then covered with clear plastic mulch, and various cultural practices to improve seedling emergence were compared. Planting dates (8, 12, and 25 Apr. 1991), seeding systems (raised bed vs. flat, 1991), and one or two rows per bed (1991 and 1992, respectively) were evaluated for their effects on stand establishment and yield. Plant stand was 60% when seed was under plastic mulch, compared to 0% when no mulch was used. Maximum plant stand was obtained 4 weeks after seeding in mulched soil. With plastic mulch, earlier (on or before 12 Apr.) season plantings were best because soil temperatures were so high (≥35C) later as to reduce plant stands. The risk of excessive high temperatures was greater when seeding was on a raised bed rather than flat ground; however, using plastic mulch, temperatures were higher, often resulting in acceptable plant stands regardless of bed arrangement. Higher yields were realized with raised beds compared to flat ground sowing. When two rows per bed were used, higher temperatures on the south side reduced emergence compared to the north side of the east–west-oriented beds. Direct seeding of pepper appears to be commercially acceptable in our Mediterranean conditions, provided seed is under plastic mulch and seeding is completed on or before 12 Apr.
J.L. Walworth, D.E. Carling, and G.J. Michaelson
Head lettuce (Lactuca sativa L.) cv. Salinas was produced in field trials in southcentral Alaska with varying planting dates, planting methods, N sources, and N application rates. Variables measured included head weight and diameter and harvest date. Nitrogen source had little effect on head weight. Direct-seeded lettuce produced heaviest beads from early plantings; transplants produced heaviest heads when planted in mid- to late season. Transplanting generally produced heavier heads than direct-seeding. Head weight of transplanted and direct-seeded lettuce was maximized with ≈112 kg N/ha. The data suggest that 112 kg N/ha may be suitable for lettuce direct-seeded or transplanted throughout the growing season.
Daniel I. Leskovar and Daniel J. Cantliffe
Transplants produced with overhead or subirrigation and plants from direct seeding using primed or nontreated `Jupiter' bell pepper (Capsicum annuum L.) seeds were evaluated for growth and yield in the field for 3 years. Early in development, overhead-irrigated (01) transplants had more basal root elongation than subirrigated (SI) transplants; however, root growth differences caused by irrigation systems in the greenhouse were minimized during late ontogeny in the field. Basal, lateral, and taproot dry weights accounted for 81%, 15%, and 4% of the total for transplants and 25%, 57%, and 18% of the total for direct-seeded plants. Direct-seeded plants maintained a more-balanced root, stem, leaf, and fruit dry matter partitioning than transplants, which allocated more dry weight (per unit of root growth) to stems, leaves, and fruits. Over all seasons, transplants exhibited significantly higher and earlier yields than direct-seeded pepper plants, and total yields were similar between SI and OI transplants and between primed and nontreated seeds.