Acidification of soils in long-term field experiments

As a consequence of intensive soil management and land use and environmental effects, soil properties can change remarkably. It is especially true for acid soils because of combined effect of pollution (heavy metals, depleting the soil buffering capacity, excess of nitrates, atmospheric deposition). Small-plot fertilization trials were initiated in 1967 to evaluate changes of soil acidity (pH) and the other environmental effects in the unfertilized and in the different fertilizer-treated plots during the long-term experimental years under controlled conditions. In the National Long-Term Field Experimental Network, four of the soil types have an acid chemical reaction. Small-plot trials were established with 4-yr crop rotations of wheat-maize-maize-wheat biculture. The NPK rates in the first 20 yr were 0, 50, 100, 150, and 200 kg N; 0, 50, 100, and 150 kg P2O5; and 0 and 100 kg K2O ha(-1) yr(-1). From the 21st yr on, the fertilizer rates increased up to 0, 100, 150, 200, and 250 kg N; 0, 60, 120, and 180 kg P2O5; 0, 100, and 150 kg K2Owheat; and 0, 200, and 250 kg K2Omaize ha(-1) yr(-1). The pH(KCI) in 1967, 1987, and 1999 in the 20-cm layers in the control plots was as follows: site Bicserd, Mollisol loam: 6.40, 5.60, and 5.04; site Karcag, Mollisol clay loam: 5.70, 4.73, and 4.62; site Kompolt, Mollisol clay loam: 5.20, 4.16, and 4.22; Site Putnok, Alfisol clay loam: 5.70, 4.48, and 4.62, respectively. Three of the soil (Karcag, Kompolt, and Putnok) lime were applied (lime rate 8.0 t ha(-1)), limestone 80% calcium carbonate in 1987. In the four replications of each fertilization treatments, two plots were limed and two plots remained unlimed. After the 32nd yr, acidity and the exchange capacity of the soils were investigated in the control plots and in two fertilized plots. After timing (20th yr) the pH of soils increased for 1-4 yr after which pH decreased again. Between the yr 20-32, the limed plots kept the same acidity level as it was in the 12th yr. It is typical on all of the soils that the soil acidification is also occurring on the zero NPK plots probably because of leaching and plant uptake of basic cations and possibly because of environmental pollution.