Substrate comparison for tomato propagation under different fertigation protocols

Authors: CHOWDHURY, MILON - THE OHIO STATE UNIVERSITY; AYALA, ALEXANDRA - THE OHIO STATE UNIVERSITY; SAMARAKOON, UTTARA - THE OHIO STATE UNIVERSITY; Altland, James

Submitted to: Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: In our previous research, we found that organic substrates, such as peat, pine bark, coir, wood fiber, and their various combinations, perform similarly or even better than synthetic substrates (such as perlite) for high-wire crop production, including tomatoes and cucumbers. In those studies, seedlings were propagated in Rockwool cubes to maintain uniform seedling quality at transplantation. For growers who are adapting new organic substrates for production, having organic substrate options for propagating a quality seedling is essential. This study aimed to compare different substrates for tomato propagation under various fertigation protocols. Rockwool, coir, wood fiber-coir mix, medium-grade pine bark, pine bark <0.64 cm, and pine bark <0.32 cm were evaluated with either overhead or sub-irrigation, sub-irrigation in varying container heights, and with varying fertilizer concentrations. Coir performed equally with rockwool under overhead irrigation with sub-irrigation trays. Peat-based mix and wood fiber-coir mix also worked similarly to rockwool under overhead irrigation, and growth increased proportionally with increasing nutrient concentration. Overall, wood fiber-coir mix performed similarly to rockwool and can be introduced as a propagation substrate along with peat and coir, whereas bark, including the finest grade, did not perform well as a propagation substrate.

Technical Abstract: Greenhouse tomato production faces multiple challenges, including the excessive use of nonrenewable substrates that are difficult to dispose of after their use. Currently, most growers propagate tomatoes in rockwool, but there is an increasing demand for sustainable media. The objective of this research was to evaluate sustainable and organic alternatives for greenhouse propagation of tomato seedlings intended for high wire production. Different organic and inorganic substrates were evaluated in three experiments, using a nutrient solution composed of a complete water-soluble fertilizer. Germination and growth parameters, including height, stem diameter, number of leaves, leaf area, foliar chlorophyll levels (SPAD), shoot fresh and dry weight, were measured. In the first experiment, which employed overhead irrigation, rockwool, coir, wood fi-ber-coir mix, medium-grade pine bark, pine bark <0.64 cm, and pine bark <0.32 cm were evaluated. Tomato germination was faster and at higher percentages with pine bark <0.64 cm. However, coir demonstrated either better or similar performance compared to rockwool after four weeks of transplantation. For the second experiment with subirrigation only, rockwool, coir, wood fiber-coir mix, fine-grade pine bark, and peat were evaluated at different container heights. Peat resulted in greater growth across all parameters, followed by wood fiber-coir mix in all container heights, while pine bark had the least growth across all measured parameters. In the third experiment with overhead irrigation, rockwool, wood fiber-coir mix, fine grade pine bark, and a commercial peat-based mixture were evaluated under different fertilizer rates (electrical conductivity 1.1 and 2.2 mS·cm-1). Wood fiber-coir mix, peat-based mix, and rockwool were the substrates with the highest values for all evaluated parameters. While all the organic substrates showed potential for use in tomato propagation, fine-grade pine bark and wood fiber-coir mix provided the best media for germination. Moreover, peat and wood fiber-coir mix showed the best media for subsequent seedling growth and demonstrated potential to be used as substitutes for rockwool.