TITLE:
Using Crop Management Scenario Simulations to Evaluate the Sensitivity of the Ohio Phosphorus Risk Index
AUTHORS:
Elizabeth A. Dayton, Christopher H. Holloman, Sakthi Subburayalu, Mark D. Risser
KEYWORDS:
Ohio P Index, Sensitivity Analysis, P Index Simulations, RUSLE2 Simulations, Crop Management Simulations
JOURNAL NAME:
Journal of Environmental Protection,
Vol.8 No.2,
February
21,
2017
ABSTRACT: Phosphorus (P) risk indices are commonly used in the
USA to estimate the field-scale risk of agricultural P runoff. Because the Ohio
P Risk Index is increasingly being used to judge farmer performance, it is
important to evaluate weighting/scoring of all P Index parameters to ensure
Ohio farmers are credited for practices that reduce P runoff risk and not
unduly penalized for things not demonstrably related to runoff risk. A
sensitivity analysis provides information as to how sensitive the P Index score
is to changes in inputs. The objectives were to determine 1) which inputs are
most highly associated with P Index scores and 2) the relative impact of each
input variable on resultant P Index scores. The current approach uses
simulations across 6134 Ohio point locations and five crop management scenarios
(CMSs), representing increasing soil disturbance. The CMSs range from all
no-till, which is being promoted in Ohio, rotational tillage, which is a common
practice in Ohio to full tillage to represent an extreme practice. Results
showed that P Index scores were best explained by soil test P (31.9%) followed
by connectivity to water (29.7%), soil erosion (13.4%), fertilizer application
amount (11.3%), runoff class (9.5%), fertilizer application method (2.2%), and
finally filter strip (2.0%). Ohio P Index simulations across CMSs one through
five showed that >40% scored 45 points (very high). Given Ohio water quality problems, the Ohio P Index
needs to be stricter. The current approach is useful for Ohio P Index
evaluations and revision decisions by spatially illustrating the impact of
potential changes regionally and state-wide.