By Dr. Thomas T. Yamashita

‘Mineral tie-up’ is the phrase commonly used by growers to describe how critical minerals are present in the soil, but they are ‘locked up’ in chemical compounds that don’t readily release these minerals for use by plants.  Tie-up doesn’t only lock minerals in the soil, it also works against the grower by creating an imbalance of available nutrients to the plant, an occurrence that the majority of growers have or will work to overcome.

In this article, we will discuss some of the most effective means of mitigating tie-up and making soil minerals available for photosynthetic processes.

Carbonation

The most effective way to free minerals of these chemical connections is to solubilize them with carbonic acid, via a process called carbonation. Carbonic acid forms when we react carbon dioxide with water, through the following process:

CO₂ + H₂O → HCO₃ + H

CaCO₃ + H + HCO₃ → Ca (HCO₃)

Insoluble calcite reacts with carbonic acid to produce readily soluble calcium carbonate.

Some of the CO₂ for the reaction is derived from the atmosphere, but most of it comes from the decomposition of organic matter. Thus, it is always a wise choice to incorporate the residue from the previous crop. This practice can generate a long list of benefits, including:

• Minimizing the opportunity for overwintering sites of pathogens
• Decomposing natural toxins such as allelopathic toxins
• Decomposing man-made pesticides
• Generating microbial activity that produces copious amounts of CO₂ for the production of carbonic acid
• Generating organic acids that serve as complexing agents for various minerals and help to maintain a buffering acidic environment
• Improving the water-holding capacity of the soil
• Improving the tilth of the soil

Hydration

This method is quite simple. In short, solid minerals can be softened by adding water. The swelling in the minerals increases their susceptibility to breakdown, via the following formula:

2FE₂O₃ + 3H₂O → 2FE₂O₃·3H₂O

Insoluble hematite is hydrated to produce the soluble minerals limonite.

Mineral Acid Acidification

There are many growers that have been enticed by using this technique. However, the recovery from this severe burning of the roots makes it a very high-risk treatment.

Microbial Activation of the Soil Surrounding the Roots

This is by far the most effective system for solving mineral tie-up, as it yields a number of advantages.

This overcomes tie-up through the use of blended fertilizer injections made throughout the season. This provides with the roots the opportunity to absorb substantial amounts of minerals while they are in a solution phase, before being locked into the soil.

Microbial activation develops and maintain a strong microbial community in the soil. This microbial activity, among other benefits, produces copious amounts of organic acids, which act as potent chelating and complexing agents. Continued microbial activation programs will eventually begin to convert the tight, impervious textural qualities of the soil to a softer, more aerated texture highly conducive to cation-exchange capacity (CEC), and with a high release factor. Organic acids, most of which can act as a buffer, can also lower absolute tie-up and begin improving overall release of minerals from the soil.

In this endeavor to mitigate severe mineral tie-up, you will find that the soil pH will be reduced, and ultimately create a soil that develops buffer capacity. Initially, these programs must be very intense. As chemical and biological parameters are improved, you can rely more heavily on periodic incrementation of the blended fertilizers and other maintenance activities in order to sustain the microbial community.

This approach of improving the soil’s textural and chemical qualities, along with repeated examinations of the soil, as well as chemical and biological analyses, will be instrumental in overcoming mineral tie-up.

For assistance in developing a soil program that will help to improve mineral availability, contact Fusion 360 for more information.

(Thumbnail image source: Tony Webster, “Enumclaw, Washington“, licensed via CC BY 2.0.)