WATER AND SOIL LOSSES AS A CONSEQUENCE OF ANT NESTING ON CITRUS
ORCHARDS IN EASTERN SPAIN. THE INFLUENCE OF LAND MANAGEMENT
Artemi Cerda1, Martin F. Jurgensen2, Maria Burguet1
de Geografia. Universitat de Valencia. Blasco Ibanez, 28, 46010-Valencia, Spain
e-mail: artemio.cerda@uv.es
2 School of Forest Resources and Environmental Science, Michigan Technological University,
Houghton, MI 49931, USA
1 Departament
Ants increase water infiltration rates by forming soil macrospores during nest construction
(Aalders et al., 1989) and due to their modification of soil properties (Cammeraat et al., 2002).
Those hydrological and pedological changes are key factors in soil formation and degradation in
semiarid environments (Eldridge, 1994). Those soil changes also reduce runoff rates and the
water available for soil erosion. However, new soil brought to the surface by ant activity could
increase the sediments available for erosion. The effect of ants on soil erosion rates will be
different under different land uses and land managements as the vegetation cover and soil
properties will be different. Previous research on orange orchards demonstrated that on
herbicide (then bare soils) the erosion rates are extremely high (Cerdà and Doerr, 2005) and
that the ants can be the key factor in controling soil erosion as they increase the infiltration rates
and reduce soil losses (Cerdà and Jurgensen, 2008). However, very little is known about the
interaction of ant and land management on soil erosion processes. The effects of ants on
different land managements (herbicide, ploughing and no tillage) have been researched under
simulated rainfall experiments on citrus orchards in eastern Spain.
Figure 1. Ant nest on no-tillage land management site.
Sixty plots on herbicide (10 on ants and 10 control), ploughing (10 on ants and 10 control) and
no tillage (10 on ants and 10 control) were built during the summer of 2007 and 60 experiments
were conducted in order to determine the effect of ants under different soil conditions. A rainfall
intensity of 43 mm h-1 was applied during 1 hour on 0,25 m 2 plots. Runoff was collected at 1minute interval and sediment concentration determined every 10 minutes.
Figure 2. Ant nest on herbicide land management site
Herbicide applications have greatly reduced plant cover (3.5 %), and increased soil erosion in
comparison to the ploughed and no tillage conditions. Ants increased soil infiltration rates on
herbicides treated soil, decreased runoff discharge and soil loss, but when the runoff reached a
high discharge the soil losses increased (2 out of 10 plots). On ant plots, five of the ten ant plots
did not have any runoff, so their infiltration rate was equal to our rainfall application of 43 mm h 1. Infiltration rates in the remaining ant plots were also high. In contrast, infiltration rates were
much lower on the twenty control plots (27.4 mm h-1), which had an average runoff of 4.3 liters
(32 % of the rainfall applied). Total runoff and runoff coefficients reflected the rapid start of
runoff on the control plots (4 minutes 30 seconds), as compared to the ten ant plots that had
runoff (26 minutes 40 seconds). Runoff sediment concentrations, sediment yields, and erosion
rates were much higher on the control plots, as compared to the ten ant plots with runoff.
However, ants bring fresh soil to the surface during nest building, which would be available for
transport during heavy rains, as our experiments show for 2 out of 10 plots where the sediment
concentration was the highest.
Figure 3. Ant plot on the no-tillage site.
On the no-tillage land management the soil losses were similar for the ant and control plots. It
ranged from 0.2 to 10 g m-2 h-1 and no significant differences were found between ant and
control plots. On the no-tillage soil location no runoff and soil loss was reached.
The effect of ants on soil erosion rates and processes is affected by land management. On
herbicide treated soils ants can be a key factor for runoff generation and soil loss, but due to the
vegetation on due to the intense ploughing on no-tillage and ploughed soils, ants do not affect
the soil and water losses rates.
Key Words. Soil erosion, ants, runoff, land management, herbicide, ploughing, no-tillage,
Spain.
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