April 1994, Volume 3, Number 1

An information service from the Lignin Institute

Micronutrients are those nutrients other than primary (N, P and K) and secondary (Ca, S and Mg) nutrients that are essential for normal growth and development of plants. They are frequently referred to as minor or trace nutrients, but their use is in amounts more than trace and their importance is certainly not minor. Since excessive use of micronutrients can be harmful or deadly, proper dosage and application are essential.

Micronutrients, by definition, include the following elements: boron, chlorine, cobalt, copper, iron, manganese, molybdenum, sodium and zinc. Application of these elements has increased with increased knowledge of their importance. Typically they are applied in granular or complexed liquid form.

Lignins, natural polymeric materials obtained as co-products of wood pulping, find use in both granular and liquid micronutrients. In granular micronutrients, they function as conditioning agents. Benefits obtained by the addition of 0.1-1% lignin during the granulation process include improved granulation and reduced in-process chute plugging. Granules conditioned with lignins have increased strength, reduced dustiness and are less prone to caking or pile set (see table below). As a result of their improved physical properties, micronutrient granules conditioned with lignin also generate less dust upon handling.

In liquid formulations, lignins act as complexing agents keeping micronutrients in an available form under pH conditions which would normally cause insolubilization. Complexed micronutrients made from lignins are easily applied and readily available to the plant. When applied as foliar sprays, they do not cause leaf burn (i.e. are non-phytotoxic). When used in soil treatment, they maintain availability longer than if the elements are applied alone. Typical lignin-based formulations for such applications range from simple (i.e. one element) to highly complex (i.e. six or more elements), and the dosage of lignin in such formulations ranges from 5-15%.

Complexed micronutrients made from lignin are weaker than those made from amine-based complexing agents such as EDTA, often an advantage for micronutrient availability to the plant. They are compatible with most pesticide formulations and urea-based fertilizers. Their use in phosphate-based fertilizers, however, depends on the specific formulation of interest, and pre-testing is suggested.

Lignins are classified by the EPA/FDA as non-toxic and are easy to handle and use. Their environmental friendliness makes them a "natural" choice in both granular and liquid products. Research to develop improved lignins for use in micronutrients is on-going and includes products with improved borate and phosphate tolerances.

ZnSO4 Granule Evaluation   Sample Hardness (psi) Strength TVA Attrition* (% fines) Dust (mg/g)   Unconditioned granules 334 8.6 22.5 Granules conditioned with 1% lignin 350 3.2 1.0   % Increase in Hardness 4.8     % Increase in Strength   62.8   % Decrease in Dust     95.5   *A measure of fines generated upon ball milling for 30 minutes with a known weight of steel balls. A reduction of fines generated is considered an increase in strength.

Selected References:

1. U.S. Patent 3,244,505 (1966), C.Adolphson and R.W. Simmons.
2. A. Wallace and R.T. Ashcroft, Soil Science 82 (3), 233 (1956).