It enhances the availability of phosphates and prevents molybdenum deficiency. It promotes the activity of earthworms and nitrogen-fixing bacteria as well as the breakdown of organic material that releases nitrogen, phosphorus, sulphur and micro-elements.
Liming also prevents the build-up of aluminium and manganese to toxic levels and corrects calcium and magnesium deficiencies.
The amount of lime to apply will depend on the specific pH, texture and cation exchange capacity or basic saturation of the soil.
The more acidic the soil, the more lime it requires. Clay soil and soil with a high organic matter content must also be limed. Apply lime once every three to four years on average in the case of heavy soil.
Test the pH again after three years to decide whether more lime is required. Less lime applied more often will eliminate the risk of applying too much lime in sandy soil.
Just before ploughing
Apply lime at any time of the year, but preferably immediately before ploughing. Unlike fertiliser, lime reacts slowly in the soil, which is why it should be applied at least six to eight weeks before planting/sowing.
Effectiveness depends on how well the lime has been mixed with the soil and particle size. Agricultural lime and dolomitic lime contain fine as well as coarse particles.
The fine material reacts quickly, while the coarser particles have a long-term effect; they should not be larger than 2mm on average, however.
Beware of applying too much lime. If soil is too alkaline, nutrients such as iron, manganese, zinc and phosphorus become inaccessible to the crop.
Also, be careful when mixing lime with fertiliser. If too much is mixed with fertiliser containing ammonia, a chemical reaction will take place that could cause ammonia loss. This problem is usually eliminated if dolomitic lime is used.
When lime and water-soluble phosphates are mixed, the latter become less accessible. Again, it’s better in this case to use dolomitic lime. Apply the mixture within a day or two, as it tends to harden.
Lime can be applied at any time after fertiliser treatment.
Agricultural lime is calcium carbonate, while dolomitic lime is a compound of roughly equal quantities of calcium carbonate and magnesium carbonate.
Dolomitic lime should be used on acid soil where a magnesium deficiency also occurs. Dolomitic lime is slightly less soluble than agricultural lime, but its neutralising effect is about 10% more effective.
This means the amount required can be reduced by 10% to achieve similar results to agricultural lime.
Slaked or building lime can be cheaper, but it absorbs moisture and is caustic and unpleasant to handle. It could also delay germination.
Source: Directorate Communication, department of agriculture, in co-operation with the Fertiliser Society of South Africa.