Tips for applying fall lime

By James Hoorman, Hoorman Soil Health Services

After crops are harvested, fall is a good time to apply lime. While lime can be applied any time,  ideally, the soil should be dry to allow good spreading with out rutting up a field. Here are some tips for fall lime spreading.  

First, get a good soil test to evaluate soil pH. Dr. Steve Culman, Ohio State University says the ideal pH is dependent upon the crop and the subsoil pH.  In western Ohio with calcareous soils (subsoils with limestone), lime is usually not needed until the subsoil pH for mineral soils gets below 6.0 for corn and soybeans and 6.2 for alfalfa.  In other parts of the state (eastern and southern Ohio), where the subsoil pH is less than 6.0 for mineral soils, additional lime is recommended after the soil pH drops to 6.2 for corn and soybean, and 6.5 for alfalfa. Western Ohio soils needs less lime to buffer soil pH. 

Second, lime regularly. Soils that are regularly limed are not as critical as soils that seldom get limed and the pH gets too low.  Regular liming maintenance gives a farmer more flexibility to lime when time and soil conditions are ideal.  Usually,  farmers time liming applications to when they take a soil test, which is every 3-4 years.

Third, lime may be slow to break down and release, so make applications before they are needed.  Most limestone, depending upon grade and fineness, take at least 6 months to break down to correct the soil pH.  When the soil pH is really low, it may take even longer and multiple lime applications may be needed. Generally, no more than 2 tons of lime are applied per acre. 

Fourth, consider the soil conditions.  Lime trucks and lime hauling equipment is heavy and may compact the soil. Dry soils and long-term no-till soil have higher structural stability for heavy equipment then wet soils or tilled soils.  About 80% of the compaction occurs on a tilled soil with the first wheel pass. 

Sometimes, lime is applied to frozen soils which limits soil compaction.  As long as the lime stays in place, this should not be a problem but lime applied to a no-till field with residue and/or a cover crop is less likely to move then lime applied to a bare soil.  Lime applied in the fall and early winter will freeze and thaw and to be shallowly soil incorporated.  On sloping fields or fields prone to flooding, lime can be washed away.  Again, residue and cover crops allow lime to stay in place.  On conventional fields, farmers often do some tillage to incorporate the lime, however; the soil is loose and may erode away.

Fifth, to be effective, lime must be applied evenly.  Sometimes lime and that is dumped in a filed can gather moisture and freeze, becoming lumpy when it is spread. Non-uniform application may cause uneven pH changes across a field.  One way to avoid this is to apply the lime quickly after being dumped in a field and before it gets wet and freezes. 

Sixth, consider the Effective Neutralizing Power (ENP) of any lime source which allows a producer to compare lime quality.  ENP considers the purity, neutralizing power (including fineness) and moisture content.  ENP tells how much the lime neutralizes soil acidity and is measured in pounds/ton. ENP is a required on any liming source and allows producers to compare liming sources as price per pound of neutralizing material.

Seventh, what is the best source of lime? Is high calcium lime better than dolomitic lime (higher in magnesium)?  Check your soil test and compare transportation line hauling costs.  Dr. Steve Culman says, soil test magnesium levels need to be greater than 50 ppm (100 lb) for optimal corn, soybean, wheat, and alfalfa production on fine (clay) to medium textured (silty) soils and greater than 35 ppm on coarse textured (sandy) soils.

On sandy soil (often lower in magnesium), dolomitic lime may be a better buy depending upon transportation costs.  Magnesium can be applied with other magnesium fertilizers, so compare costs.  Too much magnesium tends to tighten and compact clay soils. Ideally, calcium base saturation should be 65%-68% on sandy soils and up 72% on clay soils.  Magnesium base saturation needs to be a minimum of 15% on sandy soils but ideally not more than 20% on clay soils.  Calcium activates at least 146 key enzymes while magnesium is needed to make chlorophyll. If your pH is OK, adding gypsum (calcium sulphate) can increase calcium base saturation without affecting pH.  Keeping these two elements in balance is a key to keeping soils healthy.        

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