Effects of ants on water and soil losses from organically-managed citrus orchards in eastern Spain

Ants can play a key role in the erosion processes on agriculture land by modifying soil properties and increasing macropore flow. Ants are abundant in organically-managed orchards in the Mediterranean region due to climate conditions, no-till practices, no pesticide use, and the resulting vegetation cover. In order to determine the effect of ants on soil and water losses from these orchards growing on moderately-sloped land (4-8%), forty 1.0 m(2) plots (20 with ants mounts and 20 without ants - controls) were established during the summer of 2007. A rainfall simulator was used to apply 78 mm of water to each plot over a one-hour period, equivalent to a 20-year return-period thunderstorm. Runoff was collected at 1-minute intervals and sediment concentration measured every 10 minutes. Sediment concentrations were 300% higher on plots with ant mounds, but runoff rates were similar to the plots without ants. Average soil erosion rates averaged 41 kg ha(-1) h(-1) on the ant plots and 13 kg ha(-1) h(-1) on the control plots. The low erosion rates are due to the effect of the vegetation and litter cover in this organically-managed soil, which were little impacted by ant activity at the pedon scale.