Soil nutrient supply capacity is basically determined by the humus content and pH. The quantity and activity of soil microorganisms also strongly depend on the pH while microorganisms have a strong effect on the way and rate of organic matter decomposition.

Our long-term experiment presents the effect of straw-, farmyard- and green manure treatments combined with nitrogen, phosphorus and potassium fertilisers in 15 rotations.

We found acidic and slightly acidic soil with very low humus content (humus content of less than 1%) in all 15 rotations. Significant differences were found in the value of soil humus and pH among the different fertilisation methods. The soil was more acidic in the rotations of main and second crop lupine green manure with fertilisers than in rotations treated with straw-, and farmyard manure. The acidifying effect of fertilisers could be decreased by straw- and farmyard manure application.

Organic matter input had a positive impact on the humus content of soil, which is proved by the obtained results, as the highest humus content was measured in the crop rotations of medium and high doses of straw-, and farmyard manure. The humus content of the soil of lupine manure crops was lower than the soil of organic manure treatment.

Keywords: humus content, pH, long-term experiment, straw-, farmyard-, green manure, Westsik’s crop rotation