One of our customers emailed in with some questions. They wanted to know about lower pH levels and higher iron levels & potential correlations and were seeing seeing sub Boron and excess irons in tissue samples.

After some research, near as I can tell boron and iron have no interactions. Both are however affected by calcium (See chart 1).

More calcium will reduce iron uptake. Boron and silicon help to increase calcium uptake.

In low pH excess phosphorus can reduce boron uptake

High potassium can reduce boron uptake

Boron deficiency

• Reduces growth of soil bacteria.
• Poor movement of sugar and carbohydrates in the plant.
• Affects timing of maturity, pollination, and reproduction.

Some old articles on boron and silicon:

• http://blog.calciumproducts.com/posts/proper-nutrients-are-key-for-proper-maturity-and-disease-management.cfm
• http://blog.calciumproducts.com/posts/boron-.cfm
• http://blog.calciumproducts.com/posts/silcon-the-forgoten-nutrient.cfm

What about Iron?

Injury due to high soil iron concentrations is not common under neutral or high pH soil conditions. Toxic situations occur primarily on acid soils (< pH 5.0) and where excess soluble iron salts have been applied as foliar sprays or soil amendments (poor quality limestone).

The first symptoms of iron toxicity are necrotic spots on the leaves. An unusual form of iron toxicity has been observed in Michigan on organic soils and high organic sands. Some iron-rich, low pH, low manganese soils create an environment in which an interaction between the iron and manganese in the soil reduces manganese uptake by plants. The symptoms observed on the plants are of manganese deficiency, but the low plant uptake of manganese is caused by excessive available iron in the soil.

http://web1.msue.msu.edu/imp/modf1/05209708.html

Toxicity Symptoms

Iron toxicity is primarily pH related and occurs where the soil pH has dropped sufficiently to create an excess of available Iron. (I think this statement is wrong, not low pH, low calcium is the issue cmd)

As with some other nutrients, the visible symptoms of Fe toxicity are likely to be a deficiency of another nutrient. Fe toxicity can also occur when Zinc is deficient, or the soil is in a "reduced" condition caused by very wet or flooded conditions. Excess Fe can result in Dark green foliage, stunted growth of tops and roots, dark brown to purple leaves on some plants (e.g. bronzing disease of rice). http://www.spectrumanalytic.com/support/library/ff/Fe_Basics.htm

High levels of nitrogen and potassium increase iron uptake

Excessive iron can reduce uptake of manganese, additions of sulfur improve uptake of manganese

High iron can reduce zinc uptake, and low zinc uptake is often found with low manganese

Iron excess:

• Interferes with phosphorus absorption.
• Requires use of higher levels of potassium to regulate.
• Can cause Zinc deficiency

To reduce problems with excess iron make sure you have adequate levels of calcium in your soils and the pH is at least 6.5. SupeCal SO4 gypsum and SuperCal 98G limestone are great ways to ensure proper nutrient uptake.