Water flow in soil from organic dairy rotations

Abstract

SUMMARYManaged grasslands are characterized by rotations of leys and arable crops. The regime of water flow evolves during the leys because of earthworm and root activity, climate and agricultural practices (fertilizer, cutting and cattle trampling). The effects of duration of the leys, cattle trampling and fertilizer practice on the movement of water through sandy loam soil profiles were investigated in managed grassland of a dairy operation. Experiments using tracer chemicals were performed, with or without cattle slurry application, with cutting or grazing, in the 1st and the 3rd year of ley, and in winter rye. Each plot was irrigated for an hour with 18·5 mm of water containing a conservative tracer, potassium bromide; 24 h after irrigation, macropores >1 mm were recorded visually on a horizontal plan of 0·7 m2 at five depths (10, 30, 40, 70 and 100 cm). The bromide (Br−) concentration in soil was also analysed at these depths and the density of the different earthworm species were recorded. The density of macropores was not directly influenced by the factors investigated. The abundance of anecic earthworms was larger after 3 years of ley and was not affected by grazing (trampling or dung pat deposits) or fertilizer practice. The water infiltration estimated from the Br− concentration was not influenced by fertilizer practice and was reduced after 3 years of ley due to settlement, but was greater than that for the arable phase of the rotation. As shown by Br− concentration, preferential flow was induced by the grazing regime. Infiltrating water may bypass the soil matrix under similar or more extreme conditions than in the current experiment. Such hydraulic functioning in the grazing regime is expected to reduce the risk of leaching of nitrate contained in soil water.