A modern method for estimating turfgrass nutrient requirements, April 2, 2014

This is the handout for the presentation on this topic by Micah Woods, chief scientist at the Asian Turfgrass Center, on 2 April 2014 at the Vancouver Island Golf Superintendents Association meeting at Victoria Golf Club.

The presentation slides are available for download as a 6.6 MB PDF.

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Three documents explain this method. If you really want to learn about this, please take the time to download and read:

  1. Understanding turfgrass nutrient requirements
  2. Using temperature to predict turfgrass growth potential (GP) and to estimate turfgrass nitrogen use
  3. Just what the grass requires: Using minimum levels for sustainable nutrition

Introduction: What is our objective?

The overall concept is this: if there is enough of an element available to the grass, then adding more of that element as fertilizer will provide no benefit. I think we can all agree about that. Turfgrass managers will then need to answer two questions about each of the essential elements:

  1. Is enough of this element available to the grass?
  2. If yes, then no application of that element is required. If no, then how much of that element should be supplied?

Every time I talk about this, I try to explain how one can answer those questions. And every time I talk or write about this, I explain this in a slightly different way. To review some alternative explanations of this subject, see these six recent presentations, each approaching this problem from different angles:

Slides from the presentation in Korea give an alternative approach to the same topic discussed in this seminar.

The 2 goals of a nutrient management program

Last month I was reading the fertilizer section of Turgeon’s Turfgrass Management book, 8^th^ edition. He wrote,

“The goals of a nutrient management program are to ensure that (1) all essential elements are in adequate supply, and (2) to the extent possible, nutrient-use efficiency is maximized by targeting the low end of the adequate zone.”

That is, the textbook says that an ideal nutrient management program for turf will make sure that there are no nutrient deficiencies. At the same time, an ideal nutrient management program will only apply just enough of each element, letting the amount available to the turf be just adequate, but not in excess. This maximizes the effect of applied fertilizers and reduces waste; technically, the nutrient-use efficiency is the yield or quality response for each unit of fertilizer input.

Implementation of the MLSN guidelines

Those two goals, ensuring adequate supply, and maximizing nutrient-use efficiency, are addressed by the minimum levels for sustainable nutrition (MLSN) soil nutrient guidelines developed by PACE Turf and the Asian Turfgrass Center.

The article Just What the Grass Requires from the January 2014 issue of GCM explains how the MLSN guidelines were developed and how they can be used.

To participate in the continuing improvement of these guidelines, please submit samples to the Global Soil Survey, a citizen science project that allows turfgrass managers from around the world to help the turf industry become more sustainable.

Read more about the MLSN guidelines and their implementation at the MLSN Facebook page.

Three quantities we need to know

For us to be sure that there is adequate supply of a nutrient, without inadvertently supplying too much, or not enough, we need to know three quantities:

  1. How much of the element is present in the soil - we obtain this from the soil test
  2. How much of the element is used by the grass - we estimate this based on the amount of nitrogen used by the grass
  3. How much of the element is required in the soil - this is the MLSN guideline value

Once we have those amounts, we can calculate the amount of an element required as fertilizer to ensure the soil remains at or above the MLSN guideline level for an element. We add together the amount used by the grass and the amount required in the soil, and from that we subtract the amount actually in the soil. That is, we take the amount needed, and we subtract the amount present.

Fertilizer required = MLSN level + grass use - soil test

If the result of that calculation is a positive number, that is the fertilizer requirement. If the result is a negative number, that value represents the amount of excess of that element in the soil, and it is not required as fertilizer.

Waterfall charts show this in a graphical form. We express these values in the same units and then do a mass balance to find the remaining amount after various inputs or losses of the element.

Estimating nutrient update

Nitrogen requirements can be estimated by growth potential. This guide explains how.

To get started, download the climate appraisal form from PACE Turf.

The Climate Appraisal Form is a powerful tool that can serve as the foundation for all of your annual turf management planning activities. It is available using metric units (degrees C, grams and meters) or using English units (degrees F, pounds, inches). Based on climate data from the weather station that is closest to your site, it will give you an overview of the month–to–month weather, turf growth and nutrient demand conditions at your location. While the original version of this form included forecasts for nitrogen demand only, we have recently improved on the original version by including forecasts for all major nutrients.

To understand more about the importance of nitrogen in controlling nutrient demand and uptake, read the excellent article by Kussow et al. on this topic: Evidence, Regulation, and Consequences of Nitrogen-Driven Nutrient Demand by Turfgrass.