Soil acidification is a widespread problem across southern Africa, often driven by monocropping with cereals and occurring as a result of erosion, compost decomposition and soil leaching. Applying lime to soil is regarded as a key management practice in agriculture to balance pH, enhancing crop productivity, water penetration and absorption of major nutrients by crops. Most crops grow best in soils with a pH between 6.5 and 6.8. Acidity constrains crop growth below pH levels of 5.5. Agricultural lime is limestone mined as a rock that is crushed into various particle sizes ranging from course to fine particles and can be applied in areas where there is high soil-acidity due to high levels of manganese and iron. Lime texture also determines the speed of absorption in the soil; that is, fine-lime reacts more quickly than more granular lime. However, the use of lime must be managed appropriately to avoid losing other nutrients in the soil. This practice is considered climate smart as it assists with adaptation strategies through improvement of soil fertility, whilst improving productivity at modest application rates, noting that annual application is not recommended.
Before applying lime to increase lower soil pH the following should be considered. Equipment required: soil pH testing kit, protective goggles and mask, agricultural lime, shovels/forks/hoes, and disk harrow, drag harrow or hoe if available.
- Step 1: Use a pH testing strip to determine soil pH levels, making sure to test surface and sub-surface acidity.
- Step 2: Measure area of land to be treated in order to determine amount of lime for purchase. Application should be calculated as metric tonne per hectare, depending on soil pH and crop. Lime requirements will differ depending on soil type and level of acidity in the soil. Application volumes can be guided by suppliers.
- Step 3: Purchase lime according to requirements from agricultural supplier. Savings could be realised if purchasing as a group of farmers.
- Step 4: Apply lime to the soils at least two months prior to planting directly after harvesting to allow the lime to react with the soil, and positively impact the pH.
- Step 5: Mix lime and soil well in order to reduce soil acidity. This is normally achieved through disk tilling but can be done manually using a drag harrow or hoe. However, this can be an intensive process.
- Step 6: Test pH prior to planting to ensure amendments have improved soil pH.
- Step 7: Plant crops. Monitor crop performance, and harvest results with a view to understanding impact of lime treatment.
- Step 8: Following harvest, test soil pH again.
Application of lime can be part of an Integrated Soil Fertility Management (ISFM) practices.
While a practical solution, this soil amendment should be informed by research and discussion with extension officers and lime suppliers. On-farm storage and management of lime should be included in this dialogue.
- Agricultural Research Council 2013. Maize Information Guide. Pretoria, South Africa.
- Agricultural Research Council 2007. Acid Soil and Lime. Pretoria, South Africa.
- Grain SA 2013. Liming requirement; misunderstanding the difference between efficiency and quantity concepts. Pretoria, South Africa.
Benefits
- Lime treatment can assist farmers to balance pH in acidic soils, optimising water and nutrient use for crop plant growth.
- A practical and effective way to combat the negative effects of erosion, compost decomposition and leaching on soil.
- Lime does not need to applied to soil every year.
Drawbacks
- Adding lime to soils is laborious and should not be considered a short-term solution to balancing soil pH.
- Over-application or overuse of lime can negatively affect soil quality.
