Extension Notes
Susan Fox
Lyon County Extension Agent
for Agriculture/Natural Resources
July 25, 2007
New lime recommendations from the University of Kentucky, College of Agriculture went into effect this month. The past regulations had not worked well, so changes were made to ensure that farmers receive the correct lime amounts needed for their fields.
Soil acidity is one of the biggest soil factors affecting plant growth and ultimately crop yield and profitability. Most soils in Kentucky are naturally acidic so periodic applications of lime are needed to neutralize acidity and maintain crop productivity. According to Lloyd Murdock, UK Soil Specialist, lime quality can vary widely depending on the chemical properties of the stone and the particle size. Chemical properties determine the amount of acid that can be neutralized, while size equates to how quickly it will dissolve into the soil.
For more than 25 years, lime sources in the state have been tested by the Kentucky Department of Agriculture to ensure a reasonable quality was available to farmers. In the past, lime not meeting the minimum standards of 80 percent calcium carbonate, 90 percent of particles can pass through a 10-mesh wire screen sieve and 35 percent can pass through a 50-mesh wire sieve, was reported to not meet the standards. However, banning of the product’s sales for not meeting the standards has only been done through voluntary compliance by the crushed stone industry.
Chemical properties and particle size are combined into one value that quantifies the effectiveness of the lime. This is called the relative neutralizing value or RNV. UK’s lime recommendations have been based on an assumed RNV of 67 percent. However, the range of purity, fineness and RNV has made it difficult to get accurate lime recommendations from different sources of lime. In the past year, 42 percent of the lime sources did not meet the requirements. Either the fineness or the purity was below standard.
So UK has revised its recommendation. Under this new program, the Kentucky Department of Agriculture will sample and test the quality factor of ag lime sold in the state and provide the data to UK and others. UK will base new recommendations on 100 percent effective lime or a 100 percent RNV.
Because bulk lime rarely is 100 percent effective, the amount of bulk lime needed must be determined for each lime source available, based on RNV. Farmers can use a simple formula or table to determine bulk lime recommendations. For example, if UK recommends that a field needs 1.33 tons per acre of 100 percent effective lime, and the quarry has an RNV of 52, then that means 2.5 tons of lime per acre will be needed from that quarry. The formula for this is 1.33 tons per acre divided by 52, times 100. It will vary depending on the source of the lime.
If a farmer has two choices - one with an RNV of 54 and one with an RNV of 67, and the recommendation is for two tons of 100 percent effective lime, which means 3.5 tons or 3 tons, respectively, of bulk lime. And if the cost is $19 per ton to spread it, the price is $33,250 or $28,500 for 500 acres.
For more information on these new lime recommendations, contact the Lyon County Cooperative Extension Service.
Educational programs of the Kentucky Cooperative Extension Service serve all people regardless of race, color, age, sex, religion, disability or national origin.
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