Seaweed extract benefits petunia, tomato transplants

Protocol for substrate drenches, foliar spray recommended to improve postharvest life

Seaweed extracts are used widely in agriculture and horticulture production systems. Benefits of the extracts can include early seed germination and establishment, improved crop performance and yield, increased resistance to biotic and abiotic stress, and enhanced postharvest shelf life. A study in the August 2015 issue of HortTechnology determined the effects of rockweed extract, applied as a drench or foliar spray, on plant growth and drought tolerance of tomato and petunia transplants.

According to study authors Yuqi Li and Neil Mattson, rockweed (RWE) concentrate contains macro and micronutrients, amino acids, vitamins, cytokinins, auxin, and abscisic acid-like growth substances, which affect the properties of growing media, plant growth, and crop yield. To determine if rockweed could be beneficial to petunia and tomato, the researchers tested RWE applications on transplants in greenhouse experiments at Cornell University.

“In this study, drenches significantly affected substrate pH and EC and several measured elements. RWE drench increased substrate Na+, K+, Cl−, and NO3−−N. The opposite trends were found for Ca2+ concentrations,” the authors said. Analyses showed that RWE foliar sprays were not effective for improving drought tolerance of petunia and tomato, whereas substrate drenches significantly improved drought resistance of both.

“Results of the study suggested that RWE substrate drenches at 5-10 mL·L−1 are appropriate for the improvement of postharvest life of petunia and tomato transplants; however, monitoring of substrate pH should be done,” said the authors. They added that rockweed foliar sprays can improve growth of both plants. (1)

The research summary states: Seaweed extracts are widely used as plant growth regulators in agriculture and horticulture for improvement of plant growth and development. This study investigated the effects of rockweed (Ascophyllum nodosum) extract application method (foliar spray or substrate drench) and rate on growth and postharvest drought tolerance of petunia (Petunia hybrida) and tomato (Solanum lycopersicum) transplants grown in a commercial peat/perlite substrate. Foliar sprays significantly affected growth of petunia and tomato, but did not improve drought tolerance of petunia and tomato. Whereas, substrate drenches significantly improved drought tolerance of petunia and tomato compared with the control. Shoot fresh weight (FW), shoot dry weight (DW), root index (RI), and chlorophyll index (SPAD) of petunia and tomato increased significantly with increasing concentration of foliar spray rate up to 5 mL·L−1, but did not change significantly with further higher foliar spray rates. Weekly substrate drenches at 20 mL·L−1 significantly decreased FW, DW, RI, and SPAD values of petunia and tomato. In this study, substrate drench at 5–10 mL·L−1significantly increased flower number of petunia and tomato. The results of this study suggested that substrate drenches at 5–10 mL·L−1 are appropriate for the improvement of postharvest life of petunia and tomato transplants, and that foliar applications can increase plant growth. (2)


  2. Yuqi Li ,Mattson, N., HortTechnology August 2015 vol. 25 no. 4 505-510
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