Generally, the effectiveness of lime is dependent on the particle size (left). Try using liquid lime for the fastest results (right). Photos: Dr Tan Ngai Paing
Liming, the practice of adding lime to soil, is a crucial yet often neglected technique for optimising soil conditions and boosting plant growth. Unlike the immediate visual impact of fertilisers, liming’s effects are subtle and develop slowly, leading many gardeners to ignore or underestimate this vital aspect of soil management.
The impact of proper liming on plant health and garden productivity is significant, especially in regions with naturally acidic soils like Malaysia.
Understanding soil pH and its importance
Soil pH, measuring acidity or alkalinity, profoundly affects plant health and nutrient availability. The pH scale ranges from 0 (most acidic) to 14 (most alkaline), with 7 being neutral. The scale is logarithmic, meaning each unit represents a 10-fold change in acidity or alkalinity.
For most garden plants, the sweet spot lies in a slightly acidic to neutral range, typically between pH 5.5 and 6.5. This slightly acidic range optimises nutrient availability and supports beneficial soil microorganisms.
In overly acidic soils, essential nutrients like nitrogen, phosphorus, potassium and magnesium become less available to plants, potentially causing nutrient deficiencies and stunted growth.
Conversely, in overly alkaline soils, micronutrients such as iron, manganese and zinc can become less accessible.
Malaysian soils, like many tropical soils, are very often acidic due to high rainfall and intense weathering. With a typical pH range of 4 to 5, these soils are often considered very acidic for optimal growth of most garden plants, making liming a valuable practice for Malaysian gardeners.
Soil pH testing must be done with a good pH meter (right). Avoid pH meters that use metal rods that probe directly into the soil (left), as they are uncalibrated and inaccurate.
What is lime?
Lime used for soil amendment should not be confused with the citrus fruit. Agricultural lime is an alkaline material used to increase soil pH. It is derived from crushed limestone or other naturally occurring, calcium-rich minerals. The most common types used in gardening are:
1. Calcitic lime (calcium carbonate): Made from limestone, this material is the most widely used form.
2. Dolomitic lime (calcium magnesium carbonate): It contains both calcium and magnesium, and ideal for soils deficient in these nutrients.
3. Quick lime (calcium oxide): This material reacts quickly but is less popular due to safety concerns.
Liming materials can be easily purchased in plant nurseries and online stores.
Choosing the right lime and determining requirements
The effectiveness of lime depends largely on its particle size. Finer particles react more quickly with the soil, providing faster pH adjustment.
Options include powdered lime (fast-acting but dusty), pelletised lime (easier to handle), and liquid lime (fastest-acting but more costly).
To determine lime requirements:
1. Test your soil pH using a reliable pH meter, mixing soil with water for accuracy.
2. If soil pH is below 5, a general guideline is to apply 5g of lime per 2kg of soil.
3. For larger areas, soil tests conducted by professional soil laboratories will provide specific recommendations.
Application methods
Lime can be applied through surface application (spread evenly and watered in), incorporation (mixed into the top 15-20cm of soil), or split application (applied in stages for large pH adjustments). Remember that lime reacts slowly, typically taking weeks to months to fully affect soil pH. For quicker results, consider liquid lime or very finely ground products.
Proper liming requires careful attention to detail and safety. Avoid over-liming, as excessive application can disrupt nutrient balance and contribute to unnecessary carbon dioxide emissions.
To maintain optimal soil conditions, monitor your garden’s pH levels from time to time through regular testing.
When handling lime products, prioritise your safety by wearing appropriate protective gear, such as dust mask or respirator (to prevent inhalation of fine lime particles), safety goggles (to protect eyes from dust and potential splashes), chemical-resistant gloves (to prevent skin irritation), long-sleeved shirt and long pants (to minimise skin exposure), and closed-toe shoes (to protect feet from accidental spills). Exercise extra caution when working with quick lime, as it is more reactive and potentially harmful.
Always read and follow the manufacturer’s safety instructions for the specific lime product you are using.
Conclusion
Liming is a valuable tool for gardeners dealing with acidic soils, particularly in Malaysia. By understanding the science behind this practice and following proper application methods, gardeners can significantly improve soil health, leading to more vibrant and productive gardens. Remember, successful liming is about balance – regular soil testing and careful application will ensure your garden reaps the full benefits of this important soil management technique.
Dr Tan Ngai Paing is a professional chemist and senior lecturer at the Department of Land Management, Faculty of Agriculture, Universiti Putra Malaysia. He teaches the subject Management of Soil Acidity for the course Master in Tropical Soil Science.
