The degree of acidity of the soil
It has been shown that the efficiency of some pesticides, insecticides and residual herbicides applied to the soil can be affected by the degree of acidity of the soil. Soils deficient in lime absorb chemicals more strongly than well-limed soils and so the effectiveness of chemicals is reduced.
In neglecting to lime to the correct pH level, usually 6.8 or above for arable crops, farmers may be risking inadequate weed pest control in addition to the adverse effects of soil acidity on the growing crop. At a soil pH of 6 which may be satisfactory for a crop like maize it should be remembered that the activity of some herbicides is one half or less of the activity on a well limed soil.