Too much lime can be harmful

Mark A. Halcomb UT Area Nursery Specialist

I have visited two field nurseries recently with oaks with yellow foliage. The leaf veins were green with yellow interspaces. It is a classical symptom of iron chlorosis or iron deficiency.

The yellowing had come on gradually and slowly gotten worse. (Root rot can cause similar symptoms.)

Iron deficiency is caused by a high pH, or too much lime. One nursery had spread more than the soil test recommended, assuming that if a little is good, more must be better. It is not. It is very possible to add too much lime, causing problems just as serious as too little.

The other nursery knew lime was good. They spread 2 tons before planting each crop. They raise B&B plants, so this might be every 4 to 6 years. Two tons lime per acre might be a good guess every 6 years or so. But maybe not every time, in every soil.

I occasionally see where plants become yellow due to receiving the run-off from a gravel road. The calcium from the limestone gravel raises the pH, reducing the available iron.

Growers have pointed out two center rows of plants with yellow foliage and stunting caused when the lime truck made two passes on a nursery block, overlapping in the center of the block.

Excessive lime reduces the availability of the iron that is in the soil. Lowering the pH makes it available again.

Sulfur is used to lower the pH. It might take $150 to $200 worth of sulfur to counter $30 worth of lime, per acre.

It comes down to the dose, or the amount used. Many good things can be over done. One aspirin a day can prolong life, two can reduce pain. A bottle of aspirin can end life.

Lime is great. Too much causes problems. The correction is expensive. A soil test is great, a little aggravating to do, but good. A soil test is the only way to determine how much lime is required. (also phosphorus and potassium)
Soil pH has perhaps greater influence on the relative availability of plant nutrients than any other single factor. This is primarily due to the influence of the soil pH on soil microorganisms, and on the solubility of the different elements.

When soils become acid, iron, aluminum, and manganese become more soluble. Available soil phosphorus combines with this soluble iron and aluminum to form insoluble compounds.

When the soil becomes too alkaline from being over limed; copper, zinc, manganese, and iron are precipitated and become less available for plants.

The correct amount of lime increases the availability of the nutrients already present in the soil and increases fertilizer efficiency.

The efficiency of applied phosphate and potash may be more than doubled when the soil pH is increased from 5.0 to 6.1 because of less fixation or tie-up in the soil. Also, the availability of secondary and micronutrients is about optimum in the pH range of 6.1 to 6.5.

Lime promotes microbial activity required for converting some nutrients to forms that can be utilized by plants. Example: micro-organisms convert ammonium to nitrate-M, sulfur to sulfates, and enhances the breakdown of certain types of slow-release fertilizers.

(Soil reaction is whether a soil is acid, alkaline or neutral in its behavior and is expressed as pH. The pH scale ranges from 1-14, with 7 as neutral. Most Tennessee soils are acid in reaction, ranging commonly from 4.5 to 6.5.

Soils with pH values greater than 7.0 are alkaline or sweet; less than 7.0 are acid or sour. A pH of 5.0 is 10 times more acid than 6.0 and 100 times more acid than 7.0. The pH scale is logarithmic.)

For most field grown trees and shrubs, the target pH to start a multiple year crop is between 6.0 to 7.0, depending on the plant species. Birch is an exception. Lime also improves the effectiveness of triazine herbicides such as Simazine or Princep .

When needed, the correct amount of lime can increase plant growth, yields and profits. Too much lime can be applied, causing a multitude of problems, such as nutrient toxicity and unavailability.

Although lime can be applied whenever soil, weather, crop and labor conditions permit, FALL is an excellent time. Lime should be spread uniformly. Uneven distribution may present problems for several growing seasons.

Soil test every 4 to 7 years, before replanting a block of nursery stock. Develop a numbering system for all of the nursery blocks in a field to facilitate record keeping. A basic UT soil test cost $6. The turn around time is 1-2 weeks. I write the recommendations, not the lab. I must know the species to be planted in each sampled area in order to recommend the correct amount of lime for each specific block and species. I may be reached at 473-8484.