Ca content in soil (Mehlich II), variations of soil pH values and crop yields in 1990 to 1997 were evaluated at five sites with long-term stationary plant nutrition trials. Tab. I shows the site characteristics. Differentiated application rates in the particular variants and identical crop rotations were used at all sites: at Lipa and Libejovice since 1974, at Chrastava since 1977, and at Stankov and Svitavy since 1980. These crops were grown at all sites in the period of evaluation: oats with clover underseeding in 1990, meadow clover in 1991, winter wheat in 1992, potatoes in 1993, winter wheat in 1994, spring barley in 1995, potatoes in 1996, spring barley in 1997. Four fertilization variants were evaluated: var. 1 unfertilized, var. 2 farmyard manure + liming, var. 3 farmyard manure, NPK + liming, var. 4 farmyard manure + NPK. Farmyard manure was applied at a rate of 40 t/ha in fall 1992 and 1995, liming in form of limestone application was carried out the basis of soil analysis in fall 1991 and 1994 at rates of 2.8 and 1.6 t at Chrastava, 0.7 and 0.8 t at Libejovice, 2.0 and 0.8 t at Lipa, 1.2 and 0.8 t at Stankov and 2.5 and 0.8 tat Svitavy: An annual dose of phosphorus was 52.3 kg P and that of potassium 132.8 kg K (per ha). Nitrogen application rates for the separate crops (per ha): 100 kg to oats with underseeding, 140 kg to winter wheat, 160 kg to potatoes, and 92 kg to spring barley after wheat and 80 kg to spring barley after potatoes. A decrease in soil pH values and a reduction in Ca content in soil were recorded in variants without liming. Substantially higher variations were determined for variants with fertilizer applications. Regular liming (var. 2 and 3) maintained soil pH values around 6, and higher Ca concentrations in soil. A high positive correlation (r = 0.94) was calculated for the relation between pH value and Ca content in soil. The yield on unfertilized plots over eight years in total was 31.4 to 39.9 cereal units per ha at the separate sites. Yields were increased by applications of farmyard manure and liming (var. 2) against unfertilized variant by 1.6 to 15.4% subject to the site, an average increase at all sites was 10.9%. A yield increase on plots with farmyard manure and fertilizer applications (var. 4) was 47.6 to 83.7% against unfertilized variant, and 59.6% on average for all sites. The variant with farmyard manure and fertilizer applications and liming (var. 3) gave the highest yields, an increase against unfertilized variant was 59.6 to 102.8%, an average increase for all sites being 74.1%. Yields were increased by 2.0 to 17.8% by liming only (comparison of var. 3 and 4), an average increase for all sites was 9.1%. In order to maintain the required soil fertility and yield stability, applications of farmyard manure, fertilizers and liming are necessary at all sites.
