Soil acidification and liming in grassland production and grassland soil fertility in Slovenia

This paper reviews the evidences on grassland soil acidity and liming in relation to soil processes and herbage production. There is also an outline of the present state of soil acidity and acidity-related traits – contents of organic matter (OM), phosphorus (P) and potassium (K) in Slovene grassland. In grassland, soil acidification is an ongoing process under humid climate conditions. It is mainly driven by leaching of nutrients, net loss of cations due to retention in livestock products, use of physiologically acid fertilizers, acid rain and N2 fixation. This process is reduced by strong pH buffering capacity of the soil and by physiologically basic fertilizers. Acid grassland soils in Slovenia are widely distributed in spite of the fact that 44% of the total land has developed from a carbonate parent material. Of the 1713 grassland soil samples analysed during 2005-2007 45% were regarded as acid ones (pH < 5.5; in KCl), 57% as soils with very low P status (˂ 6 mg P2O5/100 g soil) and 22% as soils with very low K status (˂ 10 mg K2O/100 soil). Increased content of soil organic matter was identified for alpine pastures (˃ 10 % OM in 44% of samples), mainly as a result of low decomposition rate. Liming of acid grassland soils did not always reflect in a higher herbage yield. The cause for this inefficiency is plant composition of grassland. Thus, many grassland plants with relatively high production potential have adapted to acid soil conditions. To illustrate the inconsistent liming effect three researches are reviewed. In the first two researches liming along with fertilizer application did not increase the yield comparing to the fertilized control while in the third research the increase amounted 26 %. Liming improves considerably botanical composition of the acid grassland (e.g. sward where Common Bent – Agrostis tenuis Sibth. – prevails) and thus indirectly affects palatability and nutritive value of herbage. Grassland liming has a weak direct effect on herbage quality – it usually increases content of Ca and sometimes decreases Mg in herbage. The latter effect is rare. In Slovenia, ameliorative liming is advised for grassland soils with pH < 5.0 and maintenance liming for grassland soils with pH < 6.0 (pH in KCl or CaCl2).