Seedling Responses to Organically-Derived Plant Growth Promoters: An Effects-Based Approach.

Simon Hodge,Heng W Tan,Wendy Y Y Liu,Charles N Merfield

doi:10.3390/plants10040660

Abstract

Organically-derived biofertilizers and biostimulants, developed from harvested materials such as seaweed and waste from animal and fish processing, are currently the subject of much fundamental and applied research. These products have significant potential in reducing synthetic fertilizer inputs to horticultural, arable, and pasture-based agricultural systems, although there is frequently some ambiguity over the magnitude and consistency of any positive effects these products may have on plant performance. This study examined the effects of organically-derived plant growth promoters (PGPs) available in New Zealand on the early vegetative growth of 16 plant species maintained under glasshouse conditions. When applied as a root drench to low nutrient potting mix, the effects of the PGPs on seedling shoot growth were strongly related to the NPK contents of the applied solutions. Any positive effects on shoot growth were, on average, reduced when the seedlings were maintained in higher nutrient growing media. Applying the PGPs at concentrations twice, and four times, the recommended concentration, only caused further growth responses when the PGPs contained high levels of nutrients. Applying the PGPs as a foliar spray had negligible effects on shoot growth. Overall, the results of these trials suggest that the positive effects of applying some organically-derived PGPs on seedling growth are a function of the PGP nutrient content, and not due to any indirect effects related to phytohormone pathways or modification of rhizosphere microorganisms.

Highlights

A wide range of organic supplements, fertilizers, plant growth promoters [PGPs], and ‘biostimulants’ are available to commercial horticulturalists and home gardeners
For the trials performed in the low nutrient potting mix, we examined whether the effects of PGP root drenches were systematically related to the class of PGP class, with individual PGPs and plant species included in the model as random factors
The effects obtained for the 148 occasions when PGPs were applied as a root drench to seedlings grown in low nutrient potting mix are summarized in Figure 1

Summary

Introduction

A wide range of organic supplements, fertilizers, plant growth promoters [PGPs], and ‘biostimulants’ are available to commercial horticulturalists and home gardeners These products are frequently based on harvested organic materials, such as seaweeds, byproducts from fish processing and animal slaughterhouses, and the composting or fermentation of humic substances and compost ‘teas’ [1,2,3,4]. There are numerous reports and reviews in the scientific literature which describe how such products increase plant growth, improve plant health, and enhance yield and quality of the final produce e.g., [1,5,6,7,8] These PGPs have a general appeal to organic, sustainable, and regenerative growers on multiple levels: the biological origins of the product, the reduced reliance on synthetic fertilizers and pesticides, and, often, secondary claims of improving soil properties and microbial health [1,3]. It has been estimated that the global market for seaweed-based fertilizers alone will exceed US $17 million by 2025 [9]

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Conclusion