Seminar questions: availability (again), and foliar applications in the context of soil guidelines

After a talk at a seminar about estimating nutrient use, there were a couple questions that I answered quickly. I take the opportunity to elaborate on my answers here.

1. When looking at soil test results, how to consider the availability of nutrients?

A soil test already is measuring the availability of nutrients. The interpretation of the test result is the way the availability is assessed. For example, the MLSN guidelines have a value of 21 ppm for phosphorus (P). If the soil test result using the Mehlich 3 extractant is more than 21 ppm, then we can be confident that enough P is available to the grass. If the soil test result is less than 21 ppm, then there may not be enough available P, and P fertilizer will be recommended to increase P availability.

Soil tests by definition measure the availability. For more information on the availability topic, see concerning the availability of nutrients in soil.

2. If fertilizer applications are being made to the leaves, as a liquid, how can one use the MLSN guidelines which are for the soil?

I don’t think it matters what type of fertilizer one is applying, liquid or granular, in terms of using the MLSN guidelines. Turf grows in the soil, and turf that is growing in soil that has nutrient levels above the MLSN guidelines is almost certainly going to have access to enough of those nutrients. So when making fertilizer applications, I would choose the fertilizer product and application method based on what I want to apply, and how I want to apply it. And for the rate of application, I would make sure I was applying enough to keep the soil above the MLSN guideline. No matter the type of fertilizer used, I don’t want to grow grass in soil with nutrient levels lower than the MLSN guideline.