The changes of soil acidity in long-term fertilizer experiments

The paper describes the influence of long-term (more than 30 years) fertilizer and lime application on the soil acidity (pH(Cl)) and identifies the influence of soil acidity on the productivity of crops. At the Research Institute of Agriculture of Latvian University of Agriculture in Skriveri, a long-term subsurface drainage field experiment was established in 1981 under the guidance of professor J. Stikans on the uncultivated gleyic sod-podzolic Hypostagnic Endogleyic Albeluvisol (Hypereutric, stw-ng-AB(he)) loam. Four (slate ash with 80% neutralizing value) lime rates 0 (L0), 2.58 (L1), 5.70 (L2) and 11.40 (L3) t ha(-1) CaCO3 were used. Primary liming was done in 1981; the maintenance liming was performed in 1994 and in 2014. Four rates of mineral fertilizers: without fertilizers (F0), N45P30K45 (F1), N90P60K90 (F2) and N135P90K135 (F3) were applied annually. Since 1994, a seven-year crop rotation was created: (1) winter triticale -> (2) potatoes -> (3) spring wheat -> (4) spring oilseed rape -> (5) spring barley -> (6) and (7) perennial grasses (red clover, timothy), 1st and 2nd year of use. At the beginning of the experiment, the soil in treatments F0 and F2 was very strongly acid (pH(KCl) 4.7) but in treatments F1 and F3 - moderately acid (pH(KCl) 5.6). In limed treatments the soil acidity decreased from pH 4.8 to pH 5.8-6.0. In the following years till 1994, the soil acidity in limed treatments gradually increased (for about 0.4-0.6 pH units). After the first maintenance liming, the soil acidity reached nearly the previous highest level. Within the next twenty years, in the treatments with highest liming rate (11.40 t ha(-1) CaCO3) the soil acidity increased to pH 5.2. In treatments with low liming rate (2.58 t ha(-1) CaCO3), the soil acidity increased to pH 4.6, which was even lower than at the beginning of the experiment (pH 4.8). Without maintenance liming, the soil acidity during 20 years increased by 0.7-0.8 pH units. In the unlimed treatments, the soil acidity gradually increased from pH 4.8 to 4.4.