Changes to water repellence of soil aggregates caused by substrate-induced microbial activity

Soil microbes produce exudates which upon drying become water-repellent, thus altering hydraulic properties. The influence of microbial activity caused by adding plant nutrients on the hydraulic characteristics of soil aggregates is reported. Soil aggregates were collected from a field that had been fertilized with different amounts of nitrogen. Aggregates were also incubated with different nutrient treatments in the laboratory. Their sorptivity, hydraulic conductivity and water repellency were measured with a new device. Adding nitrogen was found to decrease sorptivity and hydraulic conductivity because of increased water repellency in the field. In the laboratory studies, the addition of nutrients caused severe water repellency in the soil aggregates. Respiration studies identified a large increase in biological activity following nutrient amendment which produces water-repellent materials.