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The Importance of Fall Liming

Fall liming is a very critical and foundational step to the success of a field.

Why is fall liming important?

Although fall is already a busy time, your soil pH continues to drop as you harvest your crop. Retired NCDA & CS Regional Agronomist, Roger Sugg, says “Successful farming is the result of wise agronomic management of production inputs and available resources. Soil tests will provide guidance for application of lime, a major input in agronomical management of soil resources.” The chemistry of soil is constantly changing with reference to soil acidity and plant available nutrients.

Sources of soil acidity include:

  • Organic matter decomposition to humus
  • Clay particles consisting of aluminum and silicon
  • Hydrous oxides of iron and aluminum
  • Exchangeable aluminum
  • Soluble salts
  • Carbon dioxide

The natural process of leaching water through the soil profile over time removes vital plant nutrients such as calcium, magnesium, and potassium as well as other nutrients from the surfaces of clay and organic matter (humus) particles in the root zone. Crop removal of nutrients, acid forming fertilizer and plant root derived hydrogen in exchange for nutrient uptake contribute to sources of soil acidity. When hydrogen and aluminum become predominate elements on surface of clay and organic matter nutrient change sites, acid soil exists in the plant root zone and lime should be applied.

When should a grower apply lime to his soils?

The best answer is as early as possible after a grower receives a soil test report recommending lime application. Lime recommendation is designed to raise the pH to the target pH for each soil type or crop target pH for some crops grown on mineral soils. Agricultural grade lime passing specifications of North Carolina lime law for guarantee of neutralizing value and fineness of grind has to have adequate time to react in soil and achieve target pH. Fall application of lime is superior to late application because coarser lime particles can require six months or more, depending on acidity level whereas fine particles react rapidly. Performance and reaction of lime not only depends on neutralizing value and fineness of particles it also depends on uniformity of application, method and depth of incorporation, soil texture, and soil acidity level.

Response to liming is beneficial to plants for various reasons.

  • Lime reacts with exchangeable aluminum, a chemical element present in acid soil, to reduce toxicity on plant roots.
  • Two essential plant nutrients, calcium and magnesium, are elements in limestone and available after lime reacts.
  • Soil properly limed has a capacity to retain potassium and other plant nutrients at increased levels on the cat-ion exchange sites of clay and the availability of phosphate fertilizer increase resulting in increased level of plant-available phosphorus.
  • Microorganism activity concerning nitrification, conversion of ammonia to nitrates, and rhizobium activity in nodule development on roots of legumes for nitrogen fixation increase in adequately limed soil.

For questions or more information, please contact your local Parkway Ag office.

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