The effect of tray cell volume and humic acid on morphological and physiological characteristics of tomato transplant (Lycopersicum esculentum Mill.)

One of the main factors affecting the growth of greenhouse tomato transplant is the choose of desired cell size or volume of the tray. So that, larger cells provide more space for better transplant growth, but as the cell volume or size increases, the space required to produce the transplants increase. Therefore, it is important to determine the appropriate cell size that produces vigorous transplants. On the other hand, improved seedling growth in various vegetables such as tomatoes due to the use of humic acid has been reported by various researchers. This study was performed to investigate the effect of tray cell volume and foliar application of humic acid on morphological and physiological characteristics of tomato transplants.

A factorial experiment in a completely randomized design with three replications and two factors include tray cell volume (15, 20 and 22 cm3) and humic acid foliar application (0, 1.5, 3.5 and 5.5 g/l) was conducted in a greenhouse at the University of Hormozgan. The growing substrates were 70% coco peat and 30% perlite. Since the fourth week onwards, with the appearance of two pairs of true leaves, the seedlings were sprayed by humic acid fertilizer with concentrations 0, 1.5, 3.5, 5.5 g/l every other day for 15 days. 7 weeks after planting, seedling characteristics such as morphological and physiological traits and concentrations of leaf N, P and K were measured. At the end of the experiment, data analysis was performed using SAS software (version: 9.1). The means were compared with Duncan test at a statistical level of 5%.

The results of this study showed that reducing of try cell volume decreased evaluated traits significantly so that the lowest mean of these traits was obtained in cell volume of 15 cm3. Reduction of cell volume from 22 to 15 cm3 significantly reduced the morphological traits including plant height, stem length, root fresh weight, fresh and dry weight of shoots, and leaf area by 12.7, 16.2, 21.9, 15.1, 18.8 and 18.4%, and physiological traits including Fv/Fm and PI by 10.7 and 25.7, respectively. Application of humic acid improved morphological and physiological characteristics of transplants and in most cases, the highest mean of under study traits were obtained by 5.5 g/l humic acid. With decreasing the tray cell volume from 22 to 15 cm3, the leaf nitrogen, phosphorus, and potassium concentration decreased by 15.7%, 18.9%, and 16.4%, respectively. However, foliar application of humic acid caused a significant increase in the leaf elements content, compared to the control. In general, the highest content of nitrogen (1033.91), phosphorus (224), and potassium (37534.94 mg/kg DW) were obtained with the application of humic acid in concentrations 3.5, 1.5, and 5.5 g/l. On the other hand, foliar application of humic acid improved the under study traits when compared to the control. Overall, these results indicate that humic acid could compensate for root growth restriction in trays with small cells.

The results of this study showed that reducing the cell volume of the tray leads to a significant reduction in physiological and morphological characteristics of tomato transplants. While the use of humic acid could improve nutrient uptake and vegetative growth of seedlings and offset the negative effects of low volume tray cell by the use of humic acid. Foliar application of humic acid improved morphological and physiological traits and absorption of nitrogen, phosphorus, and potassium. Therefore, it seems that the use of humic acid can be suggested as a strategy to produce higher quality transplants.