Assessment of soil structure of Luvisols developed from loess classified in various complexes of agricultural suitability

The objective of the study was the estimation of the aggregate size distribution and water stability of aggregates in Luvisols developed from loess, classified in three agricultural suitability complexes of soils used in Poland: very good wheat (1), good wheat (2) and deficient wheat complex (3). Soils classified in the very good wheat complex had a significantly higher content of air-dry aggregates with sizes in the range of 0.25-10 mm than those classified in the good wheat and deficient wheat complexes. The aggregate size distribution of Ap horizons of soils classified in the very good wheat complex was assessed as highly favourable, and the composition of Ap horizons of soil from the good wheat and deficient wheat complexes as favourable. The aggregate size distribution of the subsoil in the depth of 25-75 cm was assessed as favourable, while in the depth of 75-100 cm as medium favourable. The soils classified in the very good wheat and good wheat complexes were characterised by significantly higher contents of stable aggregates with sizes of 0.25-10 mm and 1-10 mm compared to the soils of the deficient wheat complex. Water stability of aggregates in the Ap horizons of soils classified in the very good wheat and good wheat complexes was estimated as good, and in the Ap horizons of soils of the deficient wheat complex as medium. Whereas, the water stability of aggregates in the Et, Bt, BC and C horizons was assessed as very poor. The reason of the deterioration of aggregate-size distribution and decrease of water-stable aggregate content with sizes of 0,25-10 mm, especially in Luvisols classified in the deficient wheat complexes was accelerated soil erosion.