Liming Tillage Soils
Where high levels are advised for tillage, half should be applied pre-ploughing and the remainder post-ploughing and then worked in. As lime takes up to two years to have its full neutralising effect on soil acidity, it should be applied well before sowing for acid sensitive crops such as beet. However, if a crop is failing due to acidity it is often worthwhile applying a lime top-dressing of 7.5 t/ha. Lime should not be applied within two years preceding a potato crop because it can increase the risk of common scab. At least 4 years should intervene between liming and sowing a seed potato crop.
Although potatoes can grow very well below pH 6.0 it is necessary to maintain the soil at a pH suitable for the rotation. The pH levels to aim for in mineral soils are about pH 6.3 for grassland, pH 6.5 for most cereals and pH 7.0 for beet, beans and peas.
Lime can take two or more years for full reaction with soil, and therefore it needs to be applied in good time. Where it is intended to plough pasture fields for tillage, they should be limed about one and a half years before cultivation or immediately after ploughing and worked into the soil. Lime should be applied two years before planting lime demanding crops such as sugar beet, peas, beans, and also wheat or barley.
Where lime has not already been applied, it should be spread after ploughing so that it can react with the soil and can be thoroughly mixed with the soil during cultivation. Where lime is spread to prevent finger and toe in brassicas, it should be spread at least twelve months before sowing the crop. Over-liming can cause problems mainly in the form of induced micronutrient deficiencies e.g. of Mn in sugar beet and oats, B in root crops, Fe in fruit plantations, and Mo induced Cu deficiency in animals. Too much lime can also prevent plant roots from taking up K and other nutrients from the soil. It can also decrease Mg availability.