Container substrate components are a potential source of micronutrients for plant growth

Abstract

The objective was to quantify the extractable micronutrient levels from container substrate components and limestone and their potential contribution as fertilizer sources for crop growth. Samples of horticultural limestone (29 samples) and substrate components [peat (48 samples), perlite (10), vermiculite (14), bark (15), and coconut coir (6)] were analyzed for micronutrient content with the SME (Saturated Medium Extract) method using either water (SME_W) or diethylenetriamine pentaacetate (SME_D) as extractants for the substrate components, or following acid digestion of limestone samples. Samples were obtained from commercial substrate and greenhouse companies throughout the U.S. and Canada. Peat included 36 peat samples from two peat bogs in Alberta Canada to evaluate whether species composition, decomposition, and bog location affected micronutrient content. Increasing von Post decomposition increased SME_W and SME_D Mn level and SME_D Zn. As percent Sphagnum fuscum increased, extractable Fe and Mn levels increased for both extractant types, and SME_W extractable Zn increased. Based on established SME guidelines for acceptable to optimum nutrient levels for soilless substrates, peat and bark could potentially provide sufficient Fe and Mn to contribute to plant requirements. Average Fe content in limestone was 0.11%, and Mn content was 0.012%. Based on SME_D extractions and lime analysis, Fe supplied by 100% peat and lime could potentially provide Fe at levels comparable with commercial pre-plant fertilizers if these Fe sources are plant-available. Substrate-pH affected solubility of Fe, Mn and Zn in peat. As substrate-pH increased, Fe and Zn solubility in peat decreased with both SME_W and SME_D. The SME_W-extractable Mn decreased with increasing pH, in contrast to SME_D-extractable Mn which increased as pH increased. Analysis of raw materials using SME_D (substrate components) or complete digestion (limestone) is advised for substrate companies to proactively identify batches of components that may affect crop nutrition. Given this high level of potential contribution of Fe by peat and lime, it is likely that these uncontrolled sources contribute to nutrient uptake in horticultural production. However, further research is required to compare extractable micronutrients with actual plant uptake.

Keywords:

• Bark
• coconut coir
• fertilizer
• lime
• peat
• perlite
• pH
• soilless substrate
• vermiculite

Acknowledgement

We thank industry partners in the Floriculture Research Alliance (floriculturealliance.org), particularly Quality Analytical Laboratories for nutritional analysis, the University of New Hampshire Agricultural Experiment Station. The use of trade names in this publication does not imply endorsement of the products named or criticism of similar ones not mentioned.

Disclosure statement

There are no competing interests associated with the publication of this article.

Additional information

Funding

This study support from the USDA-ARS Floriculture and Nursery Research Initiative [#58-3607-8-725] and HATCH FLA-ENH-005918.