MODELING DIFFUSION AND REACTION IN SOILS .6. ION DIFFUSION AND WATER CHARACTERISTICS IN ORGANIC MANURE-AMENDED SOIL

Knowledge of short-term changes in soil physical properties attributab le to manure application is a prerequisite for estimating water and so lute movement in manure-amended soils. Ion diffusivity and water trans port characteristics were measured after the application of liquid cat tle manure in two soils of different texture. Chloride diffusivity app arently decreased in a mixture of a coarse sand and 17% cattle manure compared with diffusivity in the sand without manure application. No d ifference was seen for a similar mixture using a sandy loam. A large d ry matter content in the extracted pore liquid suggested that the coar se sand with low specific surface area only adsorbed small amounts of the added manure dry matter, explaining the increased tortuosity for i on diffusion. Addition of 15-20% manure gave a large increase in water holding capacity (0.10 cm(3) cm(-3) at a soil-water potential of -150 0 cm H2O) and an increase of the Campbell soil-water retention paramet er, b, by a factor of 3 to 4 for both soils. When manure was applied b y direct injection into slits in the soil, the dry matter content of t he manure controlled the rapid initial redistribution of water. A mode l for the relative soil-liquid sorptivity (ratio of sorptivity when ap plying manure, S, to sorptivity when infiltrating water, S-0) as a fun ction of manure dry matter content is proposed.