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Bulletin E3484
A Guide for Monitoring Phosphorus


June 27, 2023 - <>

Subsurface drainage discharge and surface runoff are pathways for phosphorus (P) loss from subsurface-drained farms. Monitoring P loss is important to evaluate the P reduction performance of conservation practices. The loss of P is measured by P load.

There are three strategies for collecting water samples: (1) flow-proportional sampling, (2) time-proportional sampling, and (3) grab sampling. The sampling strategy affects the outcome of the monitoring project. Therefore, it is important to choose an appropriate sampling strategy based on the project objective. There are two general monitoring objectives: (1) estimating P load, and (2) investigating P movement.

To learn about the uncertainty of these strategies, go to the MSU Extension Drainage Website.



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