Fall is the Time to Lime

Q: Fall is the best time to apply lime. Why is that?

A: Lime takes months - not weeks -  to activate and do its work. The chemical process through which lime changes soil pH is largely unaffected by temperature but still takes months to neutralize soil acidity. This is the main reason to apply lime in fall rather than spring. But there are other good reasons to apply lime:

1. Soil pH is a major factor in the availability of nutrients. The sweet spot for nutrient availability in soil is between pH 5.8 and pH 6.5. Coastal BC soils tend to acidify, lowering the soil pH over time, so if you haven’t applied lime in a while, it is good practice to take a soil test and determine how much lime your fields need to make nutrients more available for your plants. 

2. Raising the soil pH reduces aluminum toxicity and its harmful effects. Generally speaking, the finer the soil texture the higher the clay content, and the higher the clay content in acidic soils, the higher the soluble aluminum content will be. Plants do not like aluminum, and higher concentrations of it can become toxic, resulting in a reduction in root elongation. The lower (more acid) the pH the more soluble the aluminum becomes. To make matters worse, at low soil pH, aluminum forms strong chemical bonds with important nutrients which may render them insoluble and unavailable to plants. Raising the soil pH counters these negative effects and will liberate tied up nutrients over time. 

3. Sweet or sour soil changes soil health. As soil pH lowers it becomes more acidic and may even smell sour. Sour soil is not good for plant root growth nor soil microbiology. Acidic soils will have an altered soil biome (profile) less than optimal amounts of beneficial microorganisms, which are essential for optimal root growing conditions. 

4. Lime is a great source of calcium. If soil calcium levels tend to be low, or it makes up a lower percentage of the Cation Exchange Capacity than it should, we strongly advise application of lime for both the calcium contribution and correcting the soil pH.

These are all great reasons to apply lime. But lime takes time to do its work. To really benefit from lime, applications in fall offer you the best return for your investment not only in lime, but the nutrients you apply throughout the growing season. 

Q: How much lime do I need to apply? 

A: As a general rule, the more coarse (sandy) the soil is, the less lime is required to raise (neutralize) the pH. Or vice versa, the more clay content or the finer the soil, the more lime is required to raise the soil pH. That said, you cannot “eyeball” how much lime your fields need. To determine the correct amount  you have to perform soil tests.

Simply put, to determine how much lime to apply you need a soil sample. Applying 1 or 2 mt/acre is a typical application rate, we still need to know what the condition of the soil is and what to expect. For the best lime recommendation we need the following information:

1. Soil pH and Buffer pH: with these two tests we get the bare minimum, basic information we need.
2. Soil Texture: knowing the % of sand, silt and clay is important to estimate the potential ‘reserve’ acidity we are dealing with.
3. Organic Matter (OM%): the higher the OM% the more buffered a soil is, in a sense protecting plants from the effects of aluminum. The OM% affects the target soil pH and the chosen lime application rates as well. 
4. Calcium (Ca) level and Ca as % of CEC (Cation Exchange Capacity): Ca is best supplied by lime or gypsum to soils. Ca is highly important for soil structure, soil trafficability and for plant vigour.

TerraLink’s in-house Plant Science Lab can do these test. Our Detailed Soil Test plus the Soil Texture Test provide the information needed. 

Q: I had lime applied a few years ago and it didn’t work out well. What happened? 

A: If you applied lime and didn’t get the rise in soil pH that you expected, then one or more of following situations may be to blame:

1. The soil had developed a larger reserve of soil acidity than anticipated and it became buffered to resist the change in pH from the lime.
2. Your field may have had a lower soil pH (more acid) than a single pH test revealed. Two or three composite samples from different areas of the field should be taken to get a good average representation. 
3. The pH of the soil changed since your last test. Soil pH varies throughout the year depending on what is going on in the field. Periods of water saturation, tillage, intense fertilization, manure application, crop removal, or previous lime applications all cause fluctuations in pH, including seasonal changes. Good soil samples taken yearly at similar times in good weather help remove these variables.

In any case, it is not that the lime didn’t work, but likely excess acidity was not accounted for, and hence not enough lime was applied. The quality of lime available in Coastal BC has a very high neutralizing power and, when applied in proper quantities, will not fail. 

Q: How do I get the best results for my next lime application?

A: Get regular soil tests to determine the correct amounts of lime needed, and apply lime in FALL to give it enough time to do its job. 

If you have more questions, please contact your technical sales representative or call the TerraLink Orderdesk at 1-800-661-4559.