Rockwool: Chemical and Physical Properties

Rockwool cubes are used for seed germination, and rockwool blocks and slabs as a rooting medium for growing plants hydroponically. Rockwool is marketed as a rooting medium primarily based on its water-holding capacity and aeration characteristics, rather than its elemental content.

The total elemental content of rockwool (decreasing range in %): Fe (10.5-13.4), Ca (7.30-11.8), K (1.22-1.28), Mg (3.0-0.61), Na (1.36-0.81), Zn (0.016-0.63), Mn (0.24-0.11), P (0.15-022), S (0.08-0.2), Cu (0.01-0.003), B (0.002-0.007). The variation in elemental content suggests that there is a significant “batch” effect depending on the elemental content of the source ingredients for making rockwool. How the elemental “batch” effect will impact plant nutrition needs to be determined.

Assaying rockwool as a soil, the extracted elemental content would class rockwool as a “fertile” soil. Research has shown that there is sufficient Fe in rockwool to meet the plant requirement rooted in it, and there is the potential that the elements P, K, Ca, Mg, S, Mn and Zn may also be sufficient to meet all or a portion of the elemental requirement of a rooted plant.

Rockwool is a fibrous substance, and therefore, it has a significant ion-holding capacity. Based on this fact, one needs to match an applied nutrient solution formulation (concentration and use) with the plant elemental requirement and interaction with the rooting medium.

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Dr. J. Benton Jones has written extensively on the topics of soil fertility and plant nutrition over his professional career. After obtaining a B.S. degree in Agricultural Science from the University of Illinois, he served on active duty in the U.S. Navy for two years. After discharge from active duty, he entered graduate school, obtaining M.S. and Ph.D. degrees from the Pennsylvania State University in agronomy. For 10 years, Dr. Jones held the position as research professor at the Ohio Agricultural Research and Development Center (OARDC) in Wooster. During this time, his research activities focused on the relationship between soil fertility and plant nutrition. In 1967, he established the Ohio Plant Analysis Laboratory. Joining the University of Georgia faculty in 1968, Dr. Jones designed and had built the Soil and Plant Analysis Service Laboratory building for the Georgia Cooperative Extension Service, serving as its Director for 4 years. During the period from 1972 and his retirement in 1989, Dr. Jones held various research and administrative positions at the University of Georgia. Following retirement, he and a colleague established Micro-Macro Laboratory in Athens, Georgia, a laboratory providing analytical services for the assay of soils and plant tissues as well as water, fertilizers, and other similar agricultural substances. Dr. Jones was the first President of the Soil and Plant Analysis Council and then served as its Secretary-Treasurer for a number of years. He established two international scientific journals, "Communications in Soil Science and Plant Analysis" and the "Journal of Plant Nutrition", serving as their Executive Editors during the early years of publication. Dr. Jones is considered an authority on applied plant physiology and the use of analytical methods for assessing the nutrient element status of rooting media and plants as a means for ensuring plant nutrient element sufficiency in both soil and soilless crop production settings.

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