Temperature, wetting cycles and soil texture effects on carbon and nitrogen dynamics in stabilized earthworm casts

Two soils, one a silty loam soil (Kilkea) and the other a clayey soil (Leitrim), and stabilized earthworm cast derived from both soils, were subjected to two wet-drying regimes (4 d and 16 d wetting intervals) at two temperatures (10°C and 20°C). Each treatment was sampled regularly for CO2 emissions and dissolved organic carbon, ammonium and nitrate were measured in leachate. Production of CO2 from the clayey soil was 20–40% less than from the silty loam at both temperatures and under both cycles, while production was 40% less at the lower temperature. Amounts of dissolved organic carbon (DOC) in leachate from the silty loam soil were greater than from the clayey soil, while, in general, greater amounts of DOC leached from uningested soil than from earthworm cast. Treatments with the silty loam soil lost approximately 30–40 times more total N than corresponding clayey soils under the 4 d cycle, and 12–16 times more under the 16 d cycle, thus illustrating the extent of nutrient protection in clay soils, but also the reduction of this effect with super-saturation and prolonged drying (16 d cycle). Nutrient losses suggest greater protection of nutrients in cast at first, followed by a reduction in protection (weakening of aggregate structure) in later cycles. These results have important implications for nutrient losses in the field, since significant and complex interactions were evident between the experimental factors. To improve our understanding of soil organic matter (SOM) dynamics, interactions between climatic, soil and cast-mediated changes (i.e. increased organic–inorganic interaction and burial) need to be incorporated into future models of soil decomposition.