Current Research Projects

Preferential Flow Paths in Sludge Amended Soils
Preferential flow paths are formed in soils by biological, chemical and physical processes and their interactions. Their influence is usually reflected in reduced travel time through the soil, increased solute concentrations in drainage water, or deeper penetration of chemicals into the soil profile, than predicted by conventional flow theory. Some situations that can lead to the formation and persistence of preferential flow paths have not been documented or discussed. In this proposal, one such situation, namely, the application of municipal sludge to agricultural fields, is addressed.

The application of municipal sludge may induce a change in soil permeability due to the formation of preferential flow paths. The organic matter in municipal sludge enhances the water retention capacity of a soil, making it more attractive for soil animals. Increased animal activity results in the formation of more biopores. Decaying root channels from vegetation might provide relatively larger pathways for the transfer to groundwater, of chemicals leaching from the sludge. In addition, the leachate from municipal sludge might cause the formation of synaerisis cracks in unconsolidated soils. Similar cracks have been observed in consolidated soils.

The goal of the proposed research is to characterize the effects of preferential flow paths in sludge amended soils. To achieve this goal, field and laboratory components will be melded into an integrated framework for testing the hypothesis that the application of municipal sludge to an agricultural field results in an increase in soil permeability. The field work involves the monitoring of drain flow to obtain data to test the equivalence of infiltration rate, permeability, and effluent water quality from sludge amended and non-amended plots. The laboratory analysis involves the evaluation of temporal variations in permeability from soil cores subjected to water in which the variation in water quality covers the range of the ionic strength of divalent cations measured in leachate from municipal sludge. Statistical analyses will involve the use of both parametric and nonparametric methods.

The data from this work will provide valuable information about the formation and persistence of preferential flow paths in general, and synaerisis cracks in particular, in sludge amended soils. In addition, the data will be of value in the determination of appropriate loading rates for the application of municipal sludge to agricultural land, the evaluation of competing best management practices for agriculture, and the validation of computer models that include nutrient transport to tile drains.

Optimizing Subsurface Drainage System Design
Subsurface drainage systems have almost invariably been designed to maximize crop yield. However, drainage systems can also be used to mitigate the effects of flooding, by increasing the soil water storage volume in areas that are prone to flooding.

I propose to develop two routines for the design of subsurface drainage systems, that will maximize soil storage volume without adversely affecting crop yields. The specific objectives of this project are to

Develop a routine to evaluate the region of influence of subsurface drainage systems with irregularly spaced laterals, or randomly placed drains; and to

Develop a routine for multiobjective design of subsurface drainage systems.
These routines will facilitate the identification of regions of a field that are in need of addition drainage, and will make it possible to incorporate soil storage and water quality considerations into the design of subsurface drainage systems. Potential users of the routines developed would be private, state and federal agencies responsible for soil and water resources management, such as private farmers, the Soil Conservation Service, and planners in local drainage districts.