AgriSuite: Organic Amendment Calculator

May, 5, 2021

Which field needs the nutrients or organic matter most?

Figure 1 Manure pile near side of vineyard

Organic amendments (composted manure, mushroom substrate, etc.) are valuable sources of organic matter and nutrients for orchards and vineyards. Applying nutrients to economically meet crop needs can be challenging, especially when manure or other organic amendments make up a portion of those nutrients. Understanding the nutrient analysis of the organic amendments that are being applied is important in ensuring crop needs are met while balancing fruit/vegetative growth minimizing the risk of pollution. If you don’t have a good understanding of the nutrients present in the manure or compost that you have used, it is difficult to predict the potential impact on the crop or the need for subsequent fertilizers.

Since nutrients from organic sources don’t come in pre-determined blends, OMAFRA has developed a calculator that takes sample analysis information and combines rate, timing and placement of application to determine a best estimate of available nutrients. Combined with other calculators within AgriSuite farmers can determine additional fertilizer needs or when excess nutrients could risk environmental losses for crops that have fertilizer recommendations based on soil tests. Information on fertilizer recommendations for fruit crops based on soil tests can be found at Soil Management, Fertilizer Use, Crop Nutrition and Cover Crops for Fruit Production.

The following process can be used to assess the nutrients available from the application of organic amendments.

Step 1: Sample organic amendments for nutrient analysis

The organic amendment calculator has a large database of manure samples grouped by livestock type and moisture ranges. Using this database provides a good estimate of nutrients being applied. It is recommended, however, that an actual manure analysis (that includes micronutrients) be taken at the time of application. An actual analysis will provide the most accurate assessment of applied nutrients which can vary depending on the supplier. Some organic amendments may have high levels of sodium, which can impact plant health, so having a good understanding of the composition of the amendments you are applying can be beneficial. Keeping detailed records of amendment testing results will allow for more informed decision making around fertilizer rates in the following years.

Step 2: Analyzing samples for nutrient analysis

There are a variety of labs in Ontario that will analyze organic amendments for nutrients (A&L, SGS, SAA, Honeywood). When submitting a sample to the lab for analysis at the very least, evaluate total nitrogen (N), total phosphorus (P), total potassium (K), and moisture content. It is also a good idea to have manure tested for ammonium nitrogen (NH4-N) content. Including carbon to nitrogen (C:N) ratio will also help indicate nitrogen availability. For some organic amendments (composts) it may be beneficial to also assess Sodium levels, as some composts can be high in sodium, which could implant plant health.

Step 3: Interpreting the nutrient analysis

Once the lab analysis has been received, the results can be incorporated into AgriSuite which is an interactive online collection of management tools and calculators, developed by OMAFRA that can assist you with key crop fertilization management decisions and how they relate to optimizing crop production and protecting the environment.

AgriSuite – The Organic Amendment Calculator helps determine nutrients supplied from manure inputs.
This tool will calculate the amount of crop-available nutrients ((N-P-K) and applied micronutrients) for each proposed application of organic amendments. An estimate of fertilizer equivalent value of manure N-P-K after application is also provided. https://youtu.be/1DB0JxerfP0 provides an overview of the organic amendment calculator.

This tool uses manure analysis information along with management decisions around timing, placement and rate to provide the fertilizer equivalent value of the available N-P-K applied to a field (after application) for whatever crop it was applied to.

The Organic Amendment Calculator will help you manage your soil fertility because it:

Estimates nutrients applied to a crop
Gives a guideline for additional commercial fertilizer require to balance crop needs
Provides a quick comparison of impacts of different timing or placement scenarios

Other AgriSuite calculators that can help with your crop fertility needs are:
Crop Nutrient calculator to determine crop needs and nutrient removal
the Fertilizer calculator to determine inorganic fertilizer applied or blends to meet crop requirements
the Phosphorus Loss Assessment Tool for Ontario (PLATO) to help minimize phosphorus loss from individual fields

http://ontario.ca/AgriSuite
This project was funded in part through the Canadian Agricultural Partnership (the Partnership), a federal-provincial-territorial initiative