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TECHNICAL REPORTS

Landscape and Watershed Processes

Dynamics of Potassium Leaching on a Hillslope Grassland Soil

^a National Institute for Agricultural Research (INIA), Remehue Research Station, Casilla 24-O, Osorno, Chile
^b The University of Reading, Department of Soil Science, Whiteknights, PO Box 233, Reading, Berks, RG6 6DW, UK
^c Institute of Grassland and Environmental Research (IGER), North Wyke Research Station, Okehampton, Devon, EX20 2SB, UK

^* Corresponding author (malfaro{at}remehue.inia.cl).

Received for publication October 2, 2002. There have been only a few studies of potassium (K) losses from grassland systems, and little is known about their dynamics, especially in relation to nitrogen (N) management. A study was performed during the autumn and winter of 1999 and 2000 to understand the effects of N and drainage on the dynamics of K leaching on a hillslope grassland soil in southwestern England. Two N application rates were studied (0 and 280 kg N ha^–1 yr^–1), both with and without tile drainage. Treatments receiving N also received farmyard manure (FM). Higher total K losses and K concentrations in the leachates were found in the N + FM treatments (150 and 185% higher than in 0 N treatments), which were related to K additions in the FM. Drainage reduced K losses by 35% because of an increase in dry matter production and a reduction in overland and preferential flow. The pattern of change in K concentration in the leachates was associated with preferential flow at the beginning of the drainage season and with matrix flow later in winter, and was best described by a double exponential curve. Rainfall intensity and the autumn application of FM were the main determinants of K losses by leaching. The study provided new insights into the relationships between soil hydrology, rainfall, and K leaching and its implications for grassland systems.

Abbreviations: D, drainage treatment effect • D+, drained plot • D–, undrained plot • FM, farmyard manure • MTF, mole plus tile drain flow • N, nitrogen treatment effect • N+, 280 kg N ha^–1 yr^–1 • N–, 0 kg N ha^–1 yr^–1 • OSF, overland plus subsurface lateral flow •