Properties and classification of soils of the Swedish long-term fertility experiments: V. Sites at Vreta Kloster and Högåsa

The overall objective of this study was to discover the most limiting soil properties for crop production at two fertility sites. The Vreta Kloster soil, classified as a very fine, mixed, semiactive Oxyaquic Haplocryoll, according to the Soil Taxonomy and as a Haplic Phaeozem according to the World Reference Base for Soil Resources (WRB), consisted of very dark greyish brown silty clay overlying a subsoil of heavy clay (70-80%). Porosity increased with depth due to a greater micro- but not macro-pore volume. Stocks of C and N amounted to 76.4 t C ha(-1) and 8.7 t N ha(-1) in the Ap-horizon and 24.8 t C ha(-1) and 3.25 t N ha(-1) in the subsoil to 1 m depth. Soil pH increased with depth, 6.6 to 7.4, and CEC values ranged 25 to 31 cmol(c) kg(-1) soil. The main clay minerals were illite/mica (45%) followed by vermiculite (9-20%). Chlorite and kaolinite amounted to 2% throughout the profile. In dry years, crop production at the Vreta Kloster site was greatly reduced, which can be attributed to the absence of macro-pores and high portion of micro- pores and in the subsoil reducing the amount of water available to crops. The Hogasa profile, classified as a sandy mixed Humic Dystrocryept according to the Soil Taxonomy and as Arenic Umbrisol according WRB, consisted of loamy very fine and fine sand. Soil pH and bulk density increased with depth from 5.7 to 6.5 and 1.3 to 1.6 kg dm(-3), respectively. Carbon and N stocks amounted to 72.3 t C ha(-1) and 5.9 t N ha(-1) in the Ap- horizon and were low in the subsoil, 13.5 t C ha(-1) and 1.1 t N ha(-1). Clay mineralogy was dominated by illite/mica (26-50%) with vermiculite being formed in the Ap-horizon. Chlorite amounted to 3-6% and kaolinite to 2-3% in the profile. Crop yields were less affected by rainfall conditions and leys were more productive at Hogasa than Vreta Kloster. A high mechanical resistance reducing root penetration of the subsoil and a low nutrient content limited crop production at Hogasa.