Abstract
Pollution budgets used in Total Maximum Daily Load allocation requires the determination of nutrient load at the field level. Nutrient load typically is defined as a volume multiplied by concentration of nutrient in sample and can be determined through indirect and direct approaches. Indirect approaches of measuring load such as nutrient flow models and nutrient balances do not allow field-level load calculations. Field measurements may be achieved with resin traps, soil sampling, or leachate lysimeters. Each method requires different calibration equations for field-level calculation of load from actual measurements. Ideally, lysimeters should be wide enough to collect all the water leaching below the root zone, long enough to reflect spatial variability, deep enough to allow for cultural practices above and prevent root intrusion, simple to build, allow for sample retrieval, and be cost-efficient. Existing lysimeter design was improved by increasing the length of collection container, filling the bottom part of the lysimeter with gravel, reducing depth of installation, and/or breaking water tension with a fiberglass wick. Lysimeter cost of fabrication and installation was estimated at $84 for 3.05 m long units. Because nutrient load may occur during or after a crop, lysimeter monitoring and sampling should be done year round.
