Abstract
Vegetable growers require vigorous transplants in order to reduce the period of transplant shock during early stand establishment. Organic media containing solid humic substances (HS) are amendments that have not been comprehensively explored for applications in containerized vegetable transplant production systems. In this study, HS (1% v/v) were applied to a peat-based growth medium to evaluate pre- and post-transplant growth modulation of four economically important vegetable species. Those were: pepper, tomato, watermelon, and lettuce. Seeding for all species was performed in two periods in order to evaluate their post-transplant yield performance under drought (water deficit vs. well-watered) and heat (hot vs. cool season) stresses. Compared with control, HS-treated plants had: (1) increased leaf and root biomass after transplanting due to faster growth rates; (2) lower root/shoot ratio before transplanting, but higher after 10 days of field establishment; and (3) increased root length and surface area. The negative effects of heat and drought stresses on crop yield were more prominent in control plants, while HS-treated transplants were able to mitigate yield decreases. The results clearly demonstrated the benefits of using solid HS as a management input to improve transplant quality in these crop species.
Highlights
In vegetable production, the use of containerized transplants is a standard practice to establish crops in open fields and protected environments
Lower root-to-shoot ratio (R:S) was observed in humic substances (HS)-treated plants before transplanting compared with control, but the difference disappeared after transplanting, which may be caused by the increases in root growth (RDW)
HS-treated transplants had higher yield compared with control under water stress (50% ET) in both cool (P < 0.1) and hot seasons (P < 0.05), but no differences were found in well-watered treatment (100% ET)
Summary
The use of containerized transplants is a standard practice to establish crops in open fields and protected environments. The advantages of transplants over direct seeding have been recently reviewed by Leskovar [1]: transplanting can optimize the timing and scheduling for field cultivation, shorten the cropping period, increase growth cycles, provide uniform, rapid growth and phenological synchrony (flowering, fruit set), and enhance yield and earliness. Grown transplants will negatively affect plant performance (or tolerance) in post-field establishment environments which is often accompanied by different abiotic stresses. A high-quality transplant should have an ability to bear transient or long-lasting field environmental changes, better survival and uniform stand establishment, and higher resource use efficiency, which will eventually achieve high and profitable yield [4]. Due to the limited volume of cells and short growing cycle (4 to 6 weeks), transplant quality is often determined by root developmental traits and root-to-shoot balance in the confined cells; high transplant quality is typically associated with vigorous root growth
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