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Optimising soil pH with lime to reduce emissions
Lime is a soil conditioner that adjusts soil pH by neutralising acidic soils. Using lime to optimise your soil pH can lower greenhouse gas (GHG) emissions and improve crop yields and quality.
Benefits for the environment and your farm business
Increased yield
The main benefit of optimising soil pH through liming is the increase in yields it can bring. Crops and grassland will be more productive at their optimum soil pH. For example, grass yield can be reduced by 30–40% if pH drops from 6.5 to 5.5. As well as better returns for the business, higher yields also mean fewer greenhouse gas emissions per tonne of product.
Nutrient availability
Liming may also reduce potent nitrous oxide (N2O) emissions. Optimising pH may increase microbial activity that mineralises N in the soil, making it available for plants. In these cases, less manufactured N fertiliser will be needed. This in turn avoids some of the N2O emissions from applying that fertiliser, plus the GHG emissions from its manufacture. Additionally, maintaining pH at a target level means that other macro- and micro-nutrients are optimally available from the soil.
Carbon
Liming has a mixed impact on carbon dioxide (CO2) emissions. The extracting and applying lime both emit CO2. However, liming can also help increase soil organic matter, through increasing pH and increasing microbial activity. This can store CO2 taken out of the atmosphere by plants. The response of soil organic content to pH is complex, but studies suggest that liming is a net sink for CO2 more often than it is a net source.
Financial benefits
Lime is one of the most cost-effective ways to improve soil and reduce on-farm emissions. The benefits from improved productivity and soil condition easily return the cost of using lime to reach an optimal soil pH.
Four step approach to applying lime
- A soil pH of 6.0–6.5 is considered optimum for production on mineral soils
- By analysing the soil you can determine what the land needs
- Test soil pH regularly (at least once every four years and ideally once every two years if you are a high value crop grower on a light soil) and interpret the results correctly for the soil type
- Allow enough time for any lime applied to work before retesting the soil as it will take a year to fully take effect
- If a soil test identifies deficiencies, apply the nutrients required to redress these while taking into account the soil pH requirement of what is in the cropping plan
- The volume of lime will be determined by the existing soil pH and the target pH – the target should be 0.2 pH points above optimum
- Soil texture and soil organic matter also need to be considered as, for example, to increase pH by a single unit, clay and organic soils require more lime than sandy soil.
- Consideration should also be given to specific habitats such as acid grassland and peat, where liming may be detrimental overall
- While it is important to redress lime losses and acid build-up, which mainly occur through drainage water, overusing lime is wasteful and expensive and can reduce the availability to plants of important minerals including manganese, copper and zinc and those deficiencies will be felt by livestock
- Seek professional advice if the land requires an application of calcium or magnesium lime
- Guidance is needed on the type of product to use as there are multiple different types with each suited to specific conditions e.g. calcium limestone is known to be faster acting than magnesium limestone in lifting soil pH
- Always apply lime according to crop rotation and planting schedule
- For sugar beet and barley growers, lime should be applied before planting as these crops are sensitive to soil acidity
- Don’t grow crops that are sensitive to acidity immediately after liming in situations where the soil is very acidic
- Unlike applications of nutrients, lime doesn’t need to be spread at a specific time of the year to produce the best result. However, every farmer will want to protect their soil from compaction, so apply it when ground conditions are firm and dry
- For grassland soil, apply no more than 7.5 t/ha in a single application. If any balance is needed, apply that the following year
- For cultivated soil, cultivate to 20cm after application
- Work the lime into the cultivated soil well as it can take months to increase pH throughout the topsoil. If it is important to try to achieve a rapid correction in the soil surface, top-dress with a fast-acting lime
- Lime rates can be reduced in stony soils according to the percentage of stones in the soil. For example, if stones make up 15% of soil volume, the lime rate can be reduced by 15%
- You can hire a contractor with specialist spreading equipment for the job but some types, granular lime for instance, can be applied with a standard fertiliser spreader
- Guided by GPS and soil nutrient and pH maps, lime can be spread at variable rates within fields, according to requirements
Find the optimum pH for your soil type and cropping system here
Find out more on reducing emissions on farm
Further information on liming
Learn more about nutrient management and fertiliser use
Explore how to measure and manage soil pH based on an understanding of soil texture
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