Soil productivity is determined by the inherent qualities of the soil.
The soil must be able to provide both the physical and chemical conditions necessary for plant growth.
In this blog, we’ll discuss soil productivity generally and some of the scales used to rate soil productivity in the United States.
One of the most important rating scales is called the Soil Productivity Index.
Here’s what you should know.
1. What is soil productivity?
Soil productivity refers to the ability of soil to produce crops.
It encompasses soil fertility plus the inherent and management-related factors affecting plant growth and development.
Productivity is a broader term that includes fertility as one of the important factors that contribute to crop yield.
Soil productivity is a function of several factors including management practices, irrigation, drainage, plant protection measures, climate, etc.
It’s measured in terms of harvests or crop yields relating to production factors for a specific type of soil.
Soil productivity is soil fertility plus management plus climate.
2. What’s the difference between productive soil and fertile soil?
Soil productivity is the ability of soil to produce crops.
Fertile soil is the ability of soil to supply all the essential nutrients to plants in adequate amounts, available forms, and suitable proportions (i.e., a balanced way).
Fertile soil is measured through the available forms of essential nutrient elements in the soil at any given time.
While all productive soils are fertile, not all fertile soils are productive.
For example, saline soil may have all the essential elements for plant growth, but it cannot produce anything because of the excess Na-salts.
These salts disturb the balance with other nutrient ions like calcium, magnesium, potassium, etc.
3. What is the Soil Productivity Index?
A soil productivity index is used to rate the potential yield of one soil against another over a period.
These ratings typically range from 0 to 100.
The higher numbers indicate higher production potential.
Soil productivity indexes differ by state.
The productivity index model assumes that crop yield is a function of root development, which is ultimately controlled by the soil environment.
We’ll discuss select productivity indexes below and specify the state.
4. What are the five assumptions made when soils are given a rating?
The soil has had adequate management
The soil has been under natural weather conditions (with no irrigation)
The soil has artificial drainage where required
The soil does not experience frequent flooding on lower-lying soils
The soil has no land leveling or terracing
5. What’s the advantage of using a Soil Productivity Index?
Soil productivity index ratings will remain consistent in relation to each other even when crop yields increase over time.
Having said this, you cannot compare state-specific productivity index ratings between states due to the fact that each state takes into account different values.
6. What are the 10 core characteristics of healthy, productive soil?
Good soil tilth
Soil tilth is the overall physical character of the soil in the context of its suitability for crop production.
Sufficient depth
Soil requires sufficient depth so plant roots are able to grow and function.
Shallow depth can result from a compaction layer or past erosion.
Soil with this is more susceptible to extreme fluctuations in the weather (drought, flooding, etc.).
Satisfactory (but not excessive) nutrients
For optimal plant growth, an adequate supply of nutrients is necessary.
Conversely, excess nutrients can lead to leaching and potential groundwater pollution, high nutrient run-off, greenhouse gas release, and toxicity to plants and microbial communities.
Small population of plant pathogens, insects, and pests
Plant pathogens and pests can cause diseases and damage to crops.
In healthy soil, you want the population of these organisms to be low or otherwise inactive.
This could result from direct competition with other soil organisms for nutrients or niche habitats, hyperparasitis, etc.
Additionally, healthy plants can also defend themselves better against a variety of pests just like a human with a healthier immune system.
Good soil drainage
Healthy soil drains more rapidly than unhealthy soil.
This is due to its structure and adequate distribution of different size pore spaces.
Healthy soil also retains adequate water for plant uptake.
Large population of beneficial organisms
Soil microbes are examples of beneficial organisms that are critical for soil functioning.
Microbes help with nutrient cycling, decomposition of organic matter, maintenance of soil structure, biological suppression of plant pests, etc.
To have healthy soil, you must have a high diversity of beneficial organisms to help maintain soil status and carry out various functions.
Low weed pressure
Weeds compete with crops for water and nutrients that are essential for plant growth.
As a result, weed pressure is often a major constraint on crop production.
This is because it interferes with stand establishment, blocks sunlight, hinders harvest and cultivation operations, and harbors disease-causing pathogens and pests.
No chemicals and toxins that may harm the crop
Healthy soil doesn’t contain harmful chemicals and toxins.
They can also detoxify and/or bind certain chemicals to make them unavailable for plant uptake due to their richness in stable organic matter and diverse microbial communities.
Resistance to degradation
Adverse events will happen to your soil occasionally — erosion, wind, rain, drought, vehicle compaction, etc.
Having healthy, well-aggregated soil is more resistant to these events when they occur.
Resilience when unfavorable conditions occur
When your soil is healthy, it’s able to better rebound after a negative event such as harvesting under wet soil conditions or if land constraints restrict or modify planned rotations.
7. What is the National Commodity Crop Productivity Index (NCCPI)?
The NCCPI is a national soil productivity model that is intended to be applied across state lines.
It utilizes the factors of soil, landscape, and climate to determine the rating.
However, this system can only be applied to non-irrigated or dryland agriculture, and it isn’t intended to replace any current state-specific productivity rating system.
8. How do you find your state-specific soil productivity index?
Because the land in the U.S. varies so widely, each state tackles soil productivity independently.
This means you’ll need to approach your research differently depending on where you live.
Below, we’ve provided some sample states and the resources that exist on soil productivity.
Alabama
Alabama provides information about its soil health index, acknowledging that soil supports life on Earth and provides food, fiber, and energy to sustain human life.
This page provides information about Alabama’s soil health index test as well as how to take a sample for the soil health index.
Arizona
AcreValue has compiled a list of land parcels and designated these parcels with NCCPI scores.
This can be a great resource if you’re considering purchasing land in Arizona.
See here for more information.
California
California uses the Storie Index as its method for soil rating.
This rating is based on soil characteristics that govern the land’s potential utilization and productivity capacity.
With this method, four or five parameters are evaluated: soil depth and texture, soil permeability, soil chemical characteristics, drainage (surface runoff), and climate (only if it’s not homogenous — if it is then it shouldn’t be included in the formula).
You can read more here about the Revised Storie Index.
Delaware
Similar to Arizona, AcreValue has compiled a list of land parcels and designated these parcels with NCCPI scores.
This can be a great resource if you’re considering purchasing land in Delaware.
See here for more information.
Illinois
Illinois published their soil productivity index rating nearly two decades ago.
However, since then, nearly 80 new soil types and soil complexes have been identified on Illinois county soil maps.
Visit here to learn more.
Indiana
Check this map of Indiana to see the areas with the most desirable soils based on the NCCPI — a national soil productivity index.
Iowa
In 2015, Iowa State University researchers updated the soil productivity index for the state’s soils.
The updated Corn Suitability Rating 2 (CSR2) provides an index of the inherent soil productivity of each kind of soil for row-crop production.
The index is measured on a scale of 5-100 with 100 as the most productive soils and 5 as the least.
9. How do you use the Web Soil Survey (WSS)?
The U.S. Department of Agriculture provides soil information from the National Cooperative Soil Survey.
This service is operated by the USDA Natural Resources Conservation Service (NRCS).
It provides access to the largest natural resource information system in the world.
The NRCS has soil data for more than 95 percent of the nation’s counties.
Soon, they hope to have all 100.
If you’re interested in finding out information about a certain region, then soil surveys can be particularly helpful.
Here are the basic steps to finding out additional information for farming or land purchasing purposes.
Visit here and click the green “Start WSS” button
Once in the program, use the “Area of Interest” tab to define your area
- Use the enter key or spacebar to make the image larger
- Press the escape key to close
Click the “Soil Data Explorer” tab to access soil data for your area
- This soil data can help you determine the suitability of the soils for a particular use
- The items you want saved in your report can be added to your shopping cart
- Use the same keys as above to make the image larger or press the escape key to close
Use the “Shopping Cart” tab to get your custom printable report immediately
- You can also wait and download your report later
- Use the same keys as above to make the image larger or press the escape key to close
This is a simple yet powerful tool to access and use soil data to your advantage.
If you need to know what’s beneath your feet, the information is at your fingertips.
Final Thoughts
Soil productivity is one of the essential environmental factors for ensuring the survival of humanity during the 21st century.
We must conserve the world’s soil resources so that we can continue to feed everyone who lives on Earth.
The soil productivity index can help give us an idea of crop yield.
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Disclaimer: we are not lawyers, accountants or financial advisors and the information in this article is for informational purposes only. This article is based on our own research and experience and we do our best to keep it accurate and up-to-date, but it may contain errors. Please be sure to consult a legal or financial professional before making any investment decisions.
Prior to starting Gokce Capital, Erika received a Bachelor of Architecture from the University of Southern California and a graduate degree in Urban Policy from Columbia University. She worked as both an architectural designer and engineer in New York before joining the New York City Department of Housing Preservation and Development.
Erika currently lives in the New York Metropolitan area with her spouse, daughter and cat. She is originally from Chicago and still considers herself a midwesterner at heart.
Erika also loves to read, write and travel (fun fact, she has visited all 50 states and more than 30 countries!). Her new book, Land Investing Mistakes: 11 True Stories You Need To Know Before Buying Land, is now available on Amazon.