Progress 09/01/04 to 08/31/06
Outputs
Anecic earthworms make near vertical and semi-permanent burrows which are preferential flow paths that connect the soil surface with the subsoil. Agro-chemicals may bypass the root zone through these channels, increasing the risk of ground water pollution. The positive reputation of earthworms as decomposer organisms helping with the recycling of plant residues has been questioned of late by ecologists who argue that in the northern part of North America earthworms are invasive organisms which have negative impacts on forest ecosystems. In agro-ecosystems, earthworm burrows may have direct economic impacts by increasing fertilizer loss, as well as a negative impact on ground water quality. We conducted experiments to measure whether a. percolation volume and nitrate leaching increased when anecic earthworms were present in a field plots planted to corn, b. whether the spatial distribution of earthworm plots could explain variability of percolation water collected from
the field plots. We equipped 12 plots with zero-tension lysimeters, instruments that collect water below the root zone. 4 plots each received 0, 25 and 50 earthworms (Lumbricus terrestris, common night crawlers). We measured the amount of water and the concentration of nitrate that percolated to the lysimeters for rain events. We found that more rain water percolated below the root zone in plots with earthworms than without earthworms. In the beginning of the experiments there was a relationship between the amount of water percolated and the number of earthworm burrows in a plot. The more burrows, the more percolation occurred. This relationship became weaker and all but disappeared within 6 months of the earthworm applications. The variability of percolation volume was greatest in the treatment where plots had received 25 earthworms, followed by plots with fifty worms. It was smallest for plots without added worms. We tested whether the distribution of earthworms in plots could cause
the high levels of variability in percolate in the plots with 25 earthworms. We found that earthworm burrows were randomly distributed (Poisson distribution). Given this distribution, we simulated (using Monte Carlo simulation) the likely percolation volumes 1000 times for each treatment and compared the mean and variability of percolation for the treatments with the simulation results. The means and variances of the field observations were not significantly different from the simulated variability and means. These results have bearings on the design of experiments that attempt to quantify the effects of macropores on the flow of solutes through the soil at plot and field scales. The concentration of nitrate in percolate from plots with and without earthworms was not statistically different. We calculated the mass of nitrate lost on each rain event as the concentration times the percolation volume. Even though the nitrate mass lost to below the root zone was greater in the plots with
earthworms, the high variability of the percolation volumes collected in plots with earthworms rendered the differences statistically not significant.
Impacts
Potential contributions of earthworm burrows to nitrogen leaching from no-till farm fields may represent detrimental economic effects on farm profitability and environmental costs in terms of increased ground water pollution. The spatial variability of percolation and leaching due to the spatial variation of anecic earthworm burrows may further interfere with the efficacy of precision agriculture in areas with large number of earthworms, a group of animals encouraged by no-till farm practices. The variability in the leaching patterns, if mirrored at larger scale, could impose an estimation error of crop needs within a field.
Publications
- No publications reported this period
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Progress 01/01/05 to 12/31/05
Outputs
Earthworms have been regarded as beneficial for soil quality and for growing crops. However, activity by anecic earthworms, those that create deep, vertical burrows, may cause some nutrient losses. These burrows are large pores that bypass crop root zone. Nutrient and pesticide losses below the root zone of crops may cause economic damages to the growers and also water quality degradation. To test how much nutrient is lost via earthworm burrows and whether the number of worm burrows would affect the losses, twelve 1-by-1 meter lysimeters were installed in a corn field, during May, shortly after planting, four lysimeters each receiving 0, 25, and 50 worms. Lysimeters, 30-cm long and 10-cm wide) were placed at approximately 50 cm below the soil surface at the contact between the windblown silt cap and glacial sand and gravel deposits of the Bridgehampton silt loam. The corn field received 140 kg/ha N. During the dry summer of 2005, the lysimeters did not yield
percolation water, but during a weeklong rain event in October 2005, that wetted the soil sufficiently, the lysimeters began collecting percolation water. During the five rain and snowmelt events that yielded percolate, percolate volume was not consistently related to the number of earthworm burrows and there was no significant difference among nitrate leaching values from plots with different worm burrows. However, there was a difference in the volume of water collected, with more water being collected where earthworms were applied than in plots without earthworms. The lack of difference in nitrate losses via anecic earthworm burrows may be due to the fact that during the fall of 2005 very little NO3-N was recovered. We expect that more N will be lost during the Spring 2006 as a result of fertilizing the next crop and decomposition of residue from the previous crop. Interestingly, the variability in percolation volume captured was often greatest in the 25-worm treatment, an effect
that may be related to the surface topography and the spatial aggregation/dispersal of worm burrows in the plots. To investigate this notion, worm burrow positions were surveyed shortly after worm additions in early October 2005. Between 43 and 80% of earthworms applied made visible excavation structures (middens). The midden positions were distributed randomly and followed a Poisson distribution. Using these distributions, spatial simulations were conducted and the variability in the volume of percolation found in these simulations could not be distinguished from those collected in the 50 and 25 worm treatments, suggesting that field collection of percolation in fields and forests with anecic earthworms is strongly affected by the distribution of worm burrows. Some interesting implications of this may be for the effectiveness of precision agriculture where applications of agrochemicals are metered and adjusted spatially in accordance to some indicator of need. The presence of a
sizable earthworm population and its spatial variation may affect adversely the predicted crop needs for nitrogen.
Impacts
Potential contributions of earthworm burrows to nitrogen leaching from no-till farm fields may represent detrimental economic effects on farm profitability and environmental costs in terms of increased ground water pollution. The spatial variability of percolation and leaching due to the spatial variation of anecic earthworm burrows may further interfere with the efficacy of precision agriculture in areas with large number of earthworms, a group of animals encouraged by no-till farm practices. The variability in the leaching patterns, if mirrored at larger scale, could impose an estimation error of crop needs within a field.
Publications
- Gorres J.F., Currier, J.A. and Amador, J.A. 2005. Percolation Volumes form Corn Lysimeters as a Function of Anecic Earthworm Densities. USDA-NRI Principal Investigator Meeting, Univesity of Delaware, October 26, 2005.
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Progress 01/01/04 to 12/31/04
Outputs
An assessment of burrows as potential pathways of nutrient losses will add to a body of knowledge on the effect of earthworms on the ecology and economy of agroecosystems.In order to assess whether anecic earthworms cause fertilizer-nitrogen to be lost from corn fields via their large vertical burrows, several pilot plots were established on a field at the Rhode Island Agricultural Experiment station. The field is located on a Bridgehampton silt loam. For an initial evaluation of how much water percolates through the soil, the plots were prefitted with below-ground rain gauges whose purpose it is to establish a base-line for percolation prior to field experimentation to be conducted from spring 2005 to autumn 2006. The plot studies will determine whether the presence of earthworms can have negative effects on the nutrient balance of a field.
Impacts
Potential contributions of earthworm burrows to nitrogen leaching from no-till farm fields may represent detrimental economic effects on farm profitability and environmental costs in terms of increased ground water pollution.
Publications
- No publications reported this period
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