An Overview
Using Google Earth, QGIS, and a Word Template to Measure, Calculate and Document
the Percent Slope and Distance to Water for the Calculation of
Phosphorus Site Index (PSI) and UM-Phosphorus Management Tool (UM-PMT)
On a Field by Field Basis
Maryland Nutrient Management Advisors are required to evaluate the risk of the movement of
phosphorus to water if FIV-P≥150 and additional P is desired by the producer through the
application of organic nutrients or commercial fertilizer.
This can be done accurately through the use of several computer programs. The results from this
procedure are used in RUSLE 2 evaluations and in NuMan. Table 1 provides the names of the
programs and their roles:
Table 1
Program
Google Earth
Quantum GIS (QGIS)
Word Template
Purpose
Draw property line and field boundaries for
farm map.
1. Measure distance to water.
2. Identify changes in elevation to water
with in the field.
3. Measure the distance between
elevations within the field.
4. Identify possible areas of surface
water.
5. Provide a visual guide of 10 and 35
foot buffers of that surface water.
Document calculations and how they were
developed.
Additional documents will provide the following:
 An overview of Geospatial Information System Software and QGIS
 A step by step guide to install QGIS, load files from the hard drive onto your work
computer, get to know QGIS interface and menu icons, and load the county GIS base
map.
 An explanation of how to install and use Google Earth to draw a property line and field
boundaries for a farm map.
 Procedure to load farm and field boundaries from Google Earth.
 Procedure to determine distance to water, calculate an average slope length and percent
slope, and document information in template.
 Procedure to create buffers around non-visible water on fields in QGIS, if needed.
Updated: 5/2/16