The National Commodity Crop Productivity Index (NCCPI): 1) Is a method to assess the inherent productivity of soils nationwide for commodity crops like corn, soybeans, wheat, and cotton based on soil and climate data. 2) Uses yield data relationships with soil properties from literature and the soil database to develop an index of relative productivity for each crop. 3) Shows that while some key soil properties used in the index are fixed, others like pH, organic matter, water storage, and cation exchange can be improved through management, positively or negatively impacting soil health and productivity.

1. Soil Health Implications and the
National Commodity Crop
Productivity Index (NCCPI)
Robert Dobos
(presenter-Maxine Levin)
USDA-NRCS National Soil Survey Center
Lincoln, Nebraska
(Beltsville, MD)

2. NCCPI
• A method of satisfying the need of being able to
array soils nationwide on the basis of their inherent
productivity for commodity crops
• The National Commodity Crop Productivity Index
uses the soil and site data found in the soil survey
database to assess relative soil productivity
• The model was developed using relationships of
yield to soil properties from the agronomic literature
and the relationships between commodity crop yield
to soil, site, climate, and landscape characteristics
found in the database

3. NCCPI
• The process examines the soil, site, and climatic
requirements of four crops: corn, soybeans, winter
wheat, and cotton and produces an index for each
• The index is used by other USDA agencies, realtors,
and other researchers to assess the relative
productivity of land
• The output from the model is available to the public
on Web Soil Survey and as the next slides show, is
scalable from broad to small geographic areas

6. Soil Properties and Soil Health
• Most of the soil properties used in the NCCPI are
generally use-invariant and not typically modified by
management
• However, some properties, such as pH, organic
matter content, available water storage, and cation
exchange capacity may be profoundly altered by
management, which can have either a positive or
negative impact on soil health and impact soil
productivity

7. Soil Health Related Data Used by NCCPI
• Yield data were extracted from the database and plotted
against soil property data from the database
• A spline was fitted to the data in the manner of a SMAF
curve or a sufficiency function
• The strength of the relationship at the upper boundary of
the scatterplot is of interest because it represents the effect
of a change in the plotted soil property when everything
else is close to optimum

8. Soil Health Related Data Used by NCCPI
• The upper boundary of the scatterplot can be thought of
in terms of von Liebig’s law of the minimum
• When all the other factors that impact yield are optimal,
production is controlled by the variable in least supply
• Thus, the boundary represents the maximum yield
possible at some level of the independent soil health
variable
• Keep this in mind over the next four slides

9. Soil Health Related Data Used by NCCPI –
Chemical Characteristics -- pH
• In this plot, yield data were
extracted from the
database and plotted
against surface pH
• The spline curve
represents the average
effect of pH
• The strength of the
relationship at the upper
boundary is of interest
because the slope is steep

10. Soil Health Related Data Used by NCCPI – Organic
Matter Content
• A spline fitted through the
plot shows an optimum at
about 3 percent.
• The upper boundary of
the points indicates that
even small increases in
organic matter content
can be beneficial (very
steep slope)
• The effects are greatest
in the best soils

11. Soil Health Related Data Used by NCCPI –
Available Water
• A spline fitted through
the plot shows an
optimum at about 12
cm
• The upper boundary
of the points and the
spline have nearly the
same slope indicating
increasing AWC is
almost always
beneficial

12. Soil Health Related Data Used by NCCPI – Volumetric
Cation Exchange
• Volumetric cation exchange is
the amount of exchange found
in a column of soil (in this
case 1 by 1 by 30cm tall)
rather than a mass of soil
• The spline has an optimum at
about 11 meq
• The upper boundary indicates
that under generally good
conditions, increased
exchange benefits production

13. Soil Health and NCCPI - Summary
• The NCCPI is a tool for arraying the relative productivity of
soils using the data found in the soil survey database
• Soil properties such as pH, organic matter content, available
water storage, and cation exchange can be improved through
soil health management practices
• The National Commodity Crop Productivity Index
demonstrates that the effects of changes in soil health can be
tied directly to productivity
• The productivity impacts of improvements in soil health
parameters should be most evident in the best soils

14. Thank You