Runoff Measurement to Demonstrate the Utility of a Phosphorus Index for Row Crops in the Mississippi Delta Region of Arkansas.

A Phosphorus Index is under development for row crop agriculture in Arkansas, for use as a risk assessment and nutrient management planning (NMP) tool compliant with the 2012 NRCS 590 NMP Conservation Standard.  To determine the effect of manure (poultry litter in this case) and fertilizer application on phosphorus runoff and the Phosphorus Index, runoff trials were conducted on row crop plots where management of manure, fertilizer, tillage, soil type and crops were controlled.  Trials were conducted on soybean and cotton row crop plots in the Mississippi Delta area of Arkansas.  Typical row crop fields in the Mississippi Delta feature limited land slope (0.10 percent and less) and poor drainage outlet relief, as did the trial plots.  The flat terrain and poor drainage outlets presented challenges for selecting, installing, and calibrating devices to accurately measure water and phosphorus runoff volumes.  In addition to precipitation runoff, the devices had to measure furrow irrigation runoff flows. Two devices were used to measure water runoff volumes; drop box weirs and H-flumes.  This poster presents methods used to calibrate each device, site modifications needed to install the devices, operational limitations, and a summary comparison of the advantages and disadvantages of the two runoff measuring devices to achieve the Phosphorus Index trial goals.