Managing Nitrogen in Soil-Based, Protected Crops

Monday, April 3, 2023

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