Relieving the calcium deficiency of field soils by means of liming

Over 22% of Estonian field soils are calcium-deficient and acidificated, and are also among the poorest soils in Estonia in terms of humus; their average humus content remains below 2%. Low humus content in calcium-deficient soils results from either, a lesser generation of organic matter on acid soil, or its decomposition speed as affected by the micro fungi, which are dominant in calcium-deficient (Haplic Podzoluvisols) soils. The dissolved organic matter succumbs easily to leaching and transport caused by wind and water (erosion), whereby the fertility of the soil will decline. Thus, calcium plays an important role in ensuring the fertility and sustainability of soil; liming is used to relieve its deficiency. To eliminate calcium-deficiency in field soils, the quick-acting fine dusty limes with 5-year interval 5 t ha-1 are mainly used in Estonia. Paying attention to the dynamics of available calcium content in the soil limed with fine dusty lime fertilisers, it appeared that the calcium content remained at the optimum level in the ploughed layer for only 2-3 years, a considerably shorter period of time than expected. Since the level of fineness determines its ability to dissolve and the effect of lime on the available calcium content in soil, then to improve the effectiveness of liming and, from the aspect of an economical use of resources, it is advisable to use dusty limes with a shorter than 5-year interval and, respectively, in smaller quantities, which would guarantee a more stable calcium content in the soil with a better use of resources. For longer effect, limestone should sufficiently contain a coarser fraction, dissolving only in the 3rd-4th year.