Interpreting a Compost Analysis

The incorporation of compost into your production spaces is a great way to recycle nutrients and carbon back into the soil, turning waste into something that will feed future crops and soil microbes. The variety of materials incorporated into compost, however, is highly variable. Plant residue, municipal solid waste, food processing waste, pulp or paper mill solids, manure and seafood wastes are all contenders for being included in a compost. The range of materials, each with their own broad ranges of nutrient concentrations, makes it a highly inconsistent product between batches, even where the supplier remains consistent. This variation in composition is going to have implications for nutrient management planning year to year - we can't necessarily apply the same volume from year to year and expect the same impact on our soils. 

In order to approach our nutrient management and compost applications with increased accuracy, it is recommended to submit compost samples for analysis. Nova Scotia's provincial lab services offer this as an option, and the report will break down the nutritional composition of the compost for next season's planning. Once we can better quantify the amount of nitrogen (and other key nutrients) in the compost, application volumes and a plan for additional supplementation throughout the growing season can be put together to meet the crop needs, and reduce accidental over-fertilization. 

For greenhouse soils, where all overhead precipitation has been excluded, compost analysis is especially important. Some composts tend to run high in salts (ex. calcium, magnesium etc), and while these are crucial nutrients for crop production, it is important that they are not being over-supplied to the soils. With a lack of a seasonal reset via rain and snow in protected spaces, these salts can accumulate quickly over time, impacting crop health and productivity. 

Now that we have the data...what does it mean?!

The Department of Agriculture has an interpretation document outlining the line items included in a compost analysis report and the impact that each nutrient has on crop production. Once you have a good understanding of what is included in the report, Perennia has created a fact sheet that provides further information on some of the metrics included, and the implications that these metrics have on our nutrient management plan. Below is a brief summary of some of the information presented in the factsheet, but I highly recommend you check it out for yourselves! 

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Finished composts typically contain low levels of a wide variety of nutrients (though this is highly dependent on the materials included in the mix). This lower level of nutrients can translate to a tendency to apply large volumes of compost, however this can lead to excessive levels of certain nutrients in the soil in some cases. It is typically recommended that compost is not the sole fertility source for crops, but one of a handful of additives that come together to provide the target nutrient ranges for the crop in question. 

C:N Ratios

The amount of carbon present in a compost, in relation to nitrogen, impacts nutrient cycling, and how quickly nutrients will become plant available. Composts typically range from 8:1 - 30:1. If your compost has a ratio:

•  >40:1, there is a good chance that any nitrogen that is present in the soil/compost will be 'tied up' through the process of breaking down carbon. This can lead to nitrogen deficiencies in your crop.
• 12-22:1, there is more nitrogen available than the microbes need, meaning it will become plant available more readily
• 25-32:1, it will slowly become plant available over the course of a few years.

Nitrogen

The provincial lab analysis of compost reports on total nitrogen in the sample, however nitrogen has many forms in compost. 'Organic nitrogen', which is the nitrogen included in microbial, animal and plant tissues, is not immediately plant available. It must be mineralized in the N cycle before a plant is able to take it up and use it for growth. The rate of mineralization is difficult to forecast, as it is dependent on a handful of variables (temperature, moisture, C:N ratio of the compost). When compost is the only source of nitrogen in a production system, it is challenging to match the times of peak demand for the crop, with the availability of high amounts of useable (i.e. mineral) N. 

'Mineral nitrogen', specifically ammonium-nitrogen (NH4-N) and nitrate-nitrogen (NO3-N), are the plant-available forms of nitrogen. While these are key forms for plant production, they are easily lost to the environment if they aren't immediately taken up.

How do we know the amount of available nitrogen that is present in our compost analysis? Low N composts typically have low mineral (readily available) nitrogen. High N composts usually carry a fair amount of NO3-N, which is immediately plant available. Take a look at the table below, which estimates the breakdown of organic and mineral N based on your C:N ratio, and the total N (% dry weight). This chart was taken from Perennia's fact sheet linked above, and sheds some light on the percentage of organic, or plant -unavailable, nitrogen in a compost. 

From here, we can calculate how much compost we need to add in addition to our other amendments, in order to meet the target N needs of the crop in question. 

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Utilizing and understanding the tools available to us is a key step in maximizing on-farm productivity, and the inputs invested on the farm. Compost analysis, along with soil tests and water tests, are great ways to quantify and characterize our key production components, and figure out how they can work together to hit our crop-specific nutrient targets without overshooting them. 

For those who are interested in better understanding their compost analysis results, check out Perennia's fact sheet here, or contact your commodity specialist for further discussion! 

-Talia 

Just a Reminder...it's Soil Sampling Season!

 Soil testing is a great way to understand the current nutritional status of your production space. When taken properly, the sample will give information on which nutrients are already present in the soil, the degree of nutrient availability (through CEC and pH values) and make suggestions on lime applications where needed. This information can then be used to determine the best inputs for efficient and economical crop production in the upcoming year. 

Soil sampling can be done any time of year, however most producers opt to take them in the fall immediately following harvest. The results generated through soil analysis can vary depending on the time of year, but they typically don't change a lot from the fall to the following spring. This timing also allows for a larger window to develop the fertility plan for the following season, and allows slow-acting amendments such as lime, and elemental sulfur to work their magic before the next batch of plants move in. Whichever time of year you chose to soil sample though, it should remain consistent over the years. Outdoor crops see a recommended interval of testing every 2-3 years, but protected soils (tunnels, greenhouses, etc.) should be tested on a yearly basis as it is more susceptible to big changes from year to year compared to a field soil. 

Unsure of what test you should be submitting? The field soil test is suitable for all soils, including those contained in tunnel/protected spaces. If you are a hydroponic producer, with crops grown in containers or grow bags containing soilless substrate (Ex. Sunshine mix, Promix etc), or are looking to get your potting mix tested for nutritional breakdown, then you are looking for the greenhouse soil paste analysis, listed as G1P on the general submission form for Nova Scotia's lab. 

For information on how to take a soil test, check out Perennia's latest guideline here. 

Once we have our soil test, what do all these values mean?

There are a handful of resources available to you to help interpret your soil results:

• Perennia's Soil Test Report Interpretation for Nova Scotia
• Nova Scotia's Analytical Lab's Soil Test Interpretation Ratings for Nova Scotia Crops

As always, if you have any questions regarding your soil test, feel free to reach out to your commodity specialist for further discussion.

Happy sampling folks!

-Talia 

Managing Nitrogen in Soil-Based, Protected Crops

The first session of our mini-series set the stage on some of the issues we are seeing regarding soil health and long-term resiliency in protected spaces. For those of you who missed the first session, or are interested in revisiting the teachings before building on it in part 2, you can find the full recording here (Managing Nitrogen in Protected, Soil-Based Systems). A summary of some of the information presented is listed below:

One of the re-occurring themes in protected soil production is an accumulation of nutrients, specifically things like Mg, Ca, and K, as a result of large deposits of compost before a cropping season. While these are necessary nutrients for healthy crop production and good quality fruit, too much of a good thing is not always a good thing. Typical supplementation focuses so heavily on achieving a target N value, that a lot of the micronutrients that come along with that N slip by unnoticed.

Not only are we concerned with high levels of certain micronutrients, but also have to be aware of the soil structure itself. One of the soil health indicators we talk a lot about is percent organic matter. While we like to see higher percentages of organic matter, it can come at a cost to other macro- and micro- nutrient availability to the plant when not executed properly. Paying attention to the cation exchange capacity value, or CEC, on a soil test, is important for those who regularly apply compost. While not mentioned in this webinar with Judson, the higher the CEC value, the tighter bond exists between the soil particles and the nutrients, which make it harder to make adjustments to the nutrient composition/balance without significant intervention.

Combine these two factors with the lack of overhead precipitation in tunnels, we see astronomical values of these micronutrients, which are going to contribute to a rising pH, and a significant hinderance on the plant's ability to take up all of the nutrients in the required quantities/balances that the crop needs. Here is an example of the soil test presented in the webinar highlighting this exact trend. The top image highlights a soil that has been supplemented but not to any excessive extent, and the second image highlights how that soil has evolved with continual additions of a compost:

When it comes to the use of compost in protected settings, conducting a compost analysis before application is strongly encouraged, as is yearly soil testing so that we see what is happening in these soils that do not have the same opportunities for drainage as an exposed soil would. Understanding exactly what you are putting into the soil, and how often, is crucial to avoiding buildup to the levels displayed here. Generally when it comes to supplying nutrients to the crop, scenarios that require supplementation are much easier to navigate compared to a heavily loaded and complex soil as what is projected above. The use of fertilizer blends can also contribute to the accumulation of certain nutrients. Consider this - the go-to fertilizer you use in your system is 20-20-20. While that is a great source of nitrogen, your P and K are already very high, and is going to add to the already-existing nutrient load. In soils such as these, single nutrient sources are going to be a much better choice as we attempt to remediate these soils into something that are resilient and will support crop production well into the future.

Given all of this information, what can we do to better balance out our nutrient supplementation to prevent this from happening? One of the best strategies is going to be split nutrient, application throughout the season. This is a much more targeted approach, where we know:

    1) nutritional targets for the crop in question

    2) recent soil tests outlining nutrient composition

    3) BONUS when we consider the long-term nutrient output of supplements such as                      compost or manure

From here, we are able to formulate a plan that sees regularly scheduled nutrient introduction via fertigation into the tunnels, specifically targeted for when the plant needs those nutrients the most. In doing so, we can reduce the loss of nitrogen to the environment, prevent unnecessary buildup that impede production success, maximize the impact that each $$ of fertilizer has on crop performance, and generally contributes to resilient and long-lasting productivity of those greenhouse soils.

Interested in learning how to set yourself up for split applications during the season? Join Judson Reid and Talia Plaskett at noon (AST) on April 13th for a ‘Lunch and Learn’ session on how to set yourself up for split applications of nitrogen throughout the season! This is a great opportunity to help establish the fertigation plan for 2023 and fine-tune your calculator skills to make sure that you are getting the maximum impact for every drop of fertilizer injected into the soil. For more information, or to register for the session, please check out our learning portal.
 

Posted by: Talia Plaskett

 

 

Below the Surface - What Else is your Soil Test Telling you?

 If you haven't watched Perennia's latest webinar on interpretation of soil reports...run, don't walk, to our Youtube channel! (Just kidding, you can also click here). 

Join our soil specialist Caitlin McCavour as she goes through the results generated from a soil sample submitted to the NSDA testing lab, and further explains what those values mean, and the impact it has on your crop. For the record, while this report might look similar to what is generated for a substrate-based nutrient analysis, they are not the same test! Make sure to double check the analysis you are requesting, and that it is suitable for the growing media you are using in your operation. 

Below you can find some of the questions she answers throughout the webinar: 

Go through the Elements of the Soil Test Report

What is the difference between the posted pH and the buffer pH row?

Where can I find the recommended amount of lime required for pH adjustment?

How do you select the best amendment to increase soil pH ?

Why is organic matter important?

Essential elements for plant production 

What are the ranges used to determine if my levels are low or high?

Cation Exchange Capacity

What influences the ability of a soil to have an increased or decreased ability to hold onto cations?

Who are the acidic and basic players? Are they considered equal in binding capacity?

How is this going to change your management practices?

The role of CEC in timings and volume of fertilizer applications

Base Saturation

What is base saturation?

How is it different from cation exchange capacity?

Rather than trying to summarize all of the awesome information here, I highly recommend you sit through the 52 minute webinar. If you have any questions about your soil test, and the management recommendations that go along with it, don't hesitate to reach out !