Effect of surface-casting earthworms on the transport of phosphorus and nitrogen in surface runoff from pasture |
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| Authors: | AN Sharpley JK Syers JA Springett |
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| Institution: | Department of Soil Science, Massey University, Palmerston North, New Zealand |
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| Abstract: | Treatment of a soil under permanent pasture with carbaryl (a broad spectrum carbamate biocide) resulted in a 2-fold increase in the volume of surface runoff. This was attributed to a 3-fold reduction in infiltration rate as a result of litter accumulation at the soil surface in the absence of surface-casting earthworm activity. The amounts of dissolved inorganic P (DIP), NH+4-N, and NO?3-N in surface runoff from pasture treated with carbaryl (1.18, 9.53 and 4.25 kg ha?1 yr?1, respectively) were appreciably greater than those from untreated pasture (0.31, 1.63 and 0.52 kg ha?1 yr?1). This was attributed to the large amounts of DIP, NH+4-N, and NO?13-N released from decomposing litter. Following incubation at 4°C for 18 days the release of DIP, NH+4-N and NO?3-N from litter was 160, 1600 and 950 μg g?1, respectively. Losses of particulate P and sediment in surface runoff were lower in the absence (0.31 and 290 kg ha?1 yr?1, respectively) than in the presence (0.56 and 1120 kg ha? yr?1) of surface casts, pointing to the importance of surface casts as a source of sediment. Surface casts accounted for 45 and 75%, respectively, of the annual loading of particulate P and sediment in surface runoff. Nevertheless, the total loss in surface runoff of P and N forms was increased substantially when the production of earthworm casts was eliminated |
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