7751: Crop rotation and animal manure effects on soil. II. Tilth characteristics

Schjønning, P.; Munkholm, L.J. and Elmholt, S. (2006) Crop rotation and animal manure effects on soil. II. Tilth characteristics. [preprint]

Summary

Soil structure is highly affected by soil management in arable farming. The crop rotation characteristics, the fertilization strategy and the direct impact from tillage and traffic are determining, whether soil tilth will degrade or improve. We investigated 6-7 years effect of a versatile crop rotation (CEREAL+GRASS) and the application of animal manure (CEREAL+MANURE) upon soil strength and pore characteristics, taking continuous growing of unmanured small grain cereals (CEREAL) as a common reference. A compaction treatment was applied to half of the experimental plots. The studies were applied two consecutive years to a sandy soil and a sandy loam in controlled field experiments with two replicates per treatment. A soil drop test was performed in the field to study soil fragmentation. Undisturbed soil cores and cubes were sampled for laboratory tests of pore size distribution, gas diffusivity, air permeability, and stability of aggregates in wet and dry conditions. The results confirmed the agronomically experienced poor tilth conditions of the sandy loam with a very low soil organic carbon content, while the sandy soil had a good tilth. The CEREAL+MANURE and CEREAL+GRASS systems induced better tilth conditions for both soils as compared to the CEREAL system, although not statistically significant for all trends. An interaction between cropping system and soil compaction was observed for wet aggregate stability and tensile strength of dry 8-16 mm aggregates; compaction increased stability and strength for the CEREAL and the CEREAL+MANURE systems, while it decreased these features for the CEREAL+GRASS system. Compaction reduced soil porosity in all systems but the enhanced cropping systems were less severely affected than the CEREAL system in terms of soil’s capacity to conduct air by diffusion and convection. We conclude that long-term arable farming may degrade soil tilth to critical conditions and that 6-7 years of addition of animal manure or the introduction of a diversified crop rotation may improve soil tilth as compared to a continued use of unmanured small grain cereal cropping systems.

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