The Effect of Different Tillage and Cover Crops On Soil Quality.

This paper examines the effect of different tillage treatments and cover crop on soil physical, chemical and biological properties of a sandy loam soil in a long-term field trial set up in 2007 at Foulum, Denmark. The experimental design is a split plot design with different tillage practices (direct drilling (D), harrowing (H) to a depth of 8 cm and ploughing to a depth of 20 cm (P)) as main plot. The soil was cropped with cover crop (+CC) or left without cover crop (-CC) as split plot treatments in the main plots with different tillage treatments. We assessed topsoil structural quality in field using a visual method, measured unsaturated hydraulic conductivity at -4 hPa in field and determined aggregate size distribution after a drop shatter test for soil taken from 10-20 cm depth.

The drop shatter test data showed significantly lowest mean weight diameter (MWD) for P than for H and D, indicating better friability. The interaction between cover crop and tillage treatments was significant. That is cover crop had a positive effect on direct drilling (D) (lower MWD) but not on P and H. In general there was no significant different between tillage and cover crop treatments on visual soil evaluation, although the effect of tillage was almost significant (p~0.067). Better scores were found for P than for H and D. The interaction between tillage and cover crop was almost significant (p~0.097). Cover crop tended to improve scores mainly for P. There was no treatment effect on K_unsat.

We conclude that P improved soil quality compared to H and D, especially when combined with cover crop. We also conclude that D may benefit from cover crop to yield better soil friability and hence soil quality.