Interactive effects of management practices on water-stable aggregation and organic matter of a Humic Gleysol

In many soils, the content and quality of organic matter (OM) control water-stable aggregation, which in turn preserves soil surface integrity. The effects of management practices on soil OM and aggregation remain to be determined for certain soils and climatic conditions. We assessed the effects of eight management systems involving two crop sequences: [barley (Hordeum vulgare L.) monoculture (M) and barley in rotation (R) with a forage mix of red clover (Trifolium pratense L.) and timothy (Phleum pratense L. 'Champ')], two fall tillage [moldboard plowing (MP) and chisel plowing (CP)] and two nutrient sources [liquid dairy manure (LDM) and mineral fertilizers (MIN)] on soil aggregation and OM fractions of a silty clay Humic Gleysol. Soil samples from the 0-7.5 cm layer were taken periodically during 7 yr, and the total C and N, microbial biomass C (MBC) and carbohydrate (AHC) contents, alkaline phosphatase activity (APA), and water-stable aggregation were determined. By the 7th yr, initial total C and N contents of the surface soil had increased by 35 and 45%, respectively, in R-CP-LDM. They were slightly increased in R-CP-MIN and R-MP-LDM, whereas they decreased by an average of 19% in R-MP-MIN and all monoculture plots. Increases in C contents were attributed to higher annual C inputs from forage residues and LDM, less frequent tillage in the rotation, and shallower tillage with CP. The MBC, APA, AHC and aggregation generally responded faster and to a greater degree to conservation management practices than total C and N. Overall, conservation tillage and manure applications resulted in greater improvement in surface soil conditions when used in a rotation system rather than in a monoculture. The rapid rate of changes in soil properties suggests that the surface quality of this cold silty clay soil can be improved relatively quickly with selected management combinations.