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Soils - Part 4: Soil pH

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Changing the Soil pH

Lowering soil pH

For other than small areas or for extremely high valued crops, it probably is uneconomical to attempt to reduce soil pH. For example, the amount of elemental sulfur required to reduce soil pH depends on soil texture and the amount of free calcium carbonate (lime) in the soil. The amount of elemental sulfur can range from a fraction of a ton to several tons per acre. This may be considered as part of a remedy for a high sodium saturated soil (sodic soil), if the cause of the sodium problem can be removed by tiling or irrigation water quality improvements.

Raising Soil pH

Liming: Liming acid soils to improve productivity has been a management practice for over 20 centuries. Lime is applied primarily to reduce soil acidity. Calcium deficiency has not been observed affecting plants in Nebraska. The preferred range of soil pH for most crops has already been discussed (Table 4.1).

In review, the possible benefits from liming acid soils are:
1.  Increased microbial activity, resulting in the release of some plant nutrients.
2.  Increased availability of nutrients such as phosphorus, molybdenum, potassium, calcium and magnesium.
3.  Increased nitrogen fixation for legumes by symbiotic bacteria.
4.  Alfalfa and sweet clover are easier to establish at pH of 6.5 or above.
5.  Reduction of aluminum and manganese toxicity on certain strongly acid sands. This is not yet a recognized problem in Nebraska.

To Lime or Not to Lime?

The first question concerning lime application is, 'Is it going to be profitable?' Unfortunately, the answer is not a simple “yes” or “no,” but an “it depends.'  For example, first consider the amount of lime in the irrigation water and depth to the soil’s lime layer. In general, for corn, soybean, wheat and milo production, the probability of an economical response is usually greater than 50 percent when the soil pH goes below 5.6.

The expected benefits from liming acid soils must be considered to be at least an 8- to 10-year investment. A tenant should arrange with the landlord to prorate the total cost of the lime over this period.

NebGuide G03-1503, Management Strategies to Reduce the Rate of Soil Acidification, and NebGuide G03-1504, Lime Use for Soil Acidity Management provide detailed information on what to consider when correcting soil acidity. In brief, a soil test is always necessary to determine how much lime to apply. Take care to not over-lime soils. (Sandy soils require less lime and are easier to over-lime than finer textured soils). The lime recommendation given is the amount of 60 percent Effective Calcium Carbonate lime material needed to raise the soil pH to 6.5 in a 6-inch depth of soil. More lime is required if the incorporation depth will be deeper.

No Tillage: No-till fields frequently have pH values of 5.6 or below in the top 1 to 3 inches. In these situations, reduced rates of lime can be broadcast or the producer can apply the regular rate of lime just prior to tillage.

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