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SNAP - Soil Nutrient Assessment Program

posted on 2023-11-30, 08:11 authored by USDA ARS Grassland Soil and Water Research Laboratory

SNAP (Soil Nutrient Assessment Program), a component of the USDA/ARS Soil and Water Hub, is a web-based tool that provides an estimate of plant-available nutrients that the soil naturally provides.

Soil test fertilizer recommendations have long been predicated upon response curves generated from fertility trials across the country. These response curves have been compared to relative yield which provide probability ranges for a response to varying fertilizer inputs. Category responses include very low, low, adequate, high or very high inversely related to probability of a response to various inputs of nitrogen, phosphate, and potassium (N, P, and K).

New soil test methods, increases in computing power and access to the internet have enabled development of an interactive tool that is based on plant available NPK from both the inorganic fraction and organic pool of the soil. The new methods provide an estimate of plant available nutrients that the soil naturally provides, which has largely been ignored for decades.

Since we have access to large datasets we can calculate the amounts of NPK required growing crops in lbs NPK per bu of the desired crop. For example, it requires 100 lbs of N, 50 lbs P2O5, 50 lbs K2O to grow 100 bu corn. These are the base numbers from which we subtract the soil test data after converting from the analytical ppm to Lbs P2O5 or lbs K2O. This is a straight subtraction. It also eliminates the need for "calibration data" since the soil tests reflect the soils inherent fertility. Using the example above, of 100, 50, 50 of N, P, and K required and soil test results of 25, 35, 45 then the fertilizer needed would be 75 N, 15 P2O5 and 5 K2O. This is a simple approach that doesn't get lost in relative yield-crop response curves that have been used for decades from differing geographical areas.

This tool will include current fertilizer prices, soil test inputs, and crop based county averages for the last 15 years that will predict the chances of making the yield goal the user inputs compared to historical yield data for their county and calculate the fertilizer cost with and without soil testing compared to user input yield goal and county average. This tool will allow the user via the internet to produce a more straightforward approach to realistically planning next year's fertilizer inputs and associated cost. It will also show the benefits of soil testing for increased fertilizer efficiency and reduced environmental impact.

Resources in this dataset:

  • Resource Title: Website Pointer to SNAP - Soil Nutrient Assessment Program.

    File Name: Web Page, url:

    The web dashboard interface for estimating local yield based on field location (state/county), crop (, area, and yield goal; and soil NPK test results (lb/acre), Results returned illustrate local yield, fertilizer cost/acre, fertilizer needed (lb/acre), and overall chance of success (%).


Agricultural Research Service


Data contact name

White, Mike

Data contact email


USDA Agricultural Research Service


  • Not specified

Geographic Coverage


Geographic location - description

Contiguous United States

ISO Topic Category

  • biota
  • environment
  • farming
  • geoscientificInformation
  • inlandWaters
  • planningCadastre

National Agricultural Library Thesaurus terms

soil nutrients; USDA; soil; Internet; nutrients; fertilizers; probability; nitrogen; phosphates; potassium; phosphorus; methodology; nutrient availability; data collection; crops; corn; prices; soil analysis; planning; environmental impact; computer software; crop yield; production costs; fertilizer application

OMB Bureau Code

  • 005:18 - Agricultural Research Service

OMB Program Code

  • 005:040 - National Research

ARS National Program Number

  • 211
  • 212
  • 215

Pending citation

  • No

Public Access Level

  • Public

Preferred dataset citation

USDA ARS Grassland Soil and Water Research Laboratory (2018). SNAP - Soil Nutrient Assessment Program. USDA Agricultural Research Service.