Water flow in soil from organic dairy rotations

Managed grasslands are characterized by rotations of leys and arable phases. Soil structure is inherited from the last tillage operations (ploughing, harrowing) and evolves during the leys because of climate, earthworms and roots activity, fertilisation, cutting operations or cattle trampling. We tested the effects of the duration of the leys, cattle trampling, and fertilisation on the infiltration of water in the soil profile in managed grasslands. The experiment was situated within the dairy crop rotation on loamy sand at the Foulum experimental farm (Denmark). Irrigation experiments were performed in the 1st and the 3rd year of pasture, with or without slurry application or grazing, and in winter rye. Each plot was irrigated during an hour with 18.5 mm of water containing a non-reactive tracer (KBr). 24 hours after the irrigation, macropores larger than 1 mm were recorded on horizontal plan at five depths (0.1, 0.3, 0.4, 0.75 and 1.0 m), Bromide concentration in soil was analysed at the same depths and the density of earthworm was recorded. The density of macropores was not directly influenced by the factors tested. Abundance of anecic earthworms was larger after three years of pasture and was not affected by grazing or by fertilisation. Water infiltration rate was not influenced by fertilisation. Infiltration rate was reduced after three years of pasture due to settlement, but exceeded infiltration rate in the arable phase of the rotation. Infiltration pattern in plots in grazing regime indicated occurrence of preferential flows down to 0.4 m depth. Rain water may bypass the soil matrix under similar or more extreme conditions than this experiment. We expect such hydraulic functioning to reduce the risk of leaching the nitrate contained in the soil water