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Slides from a presentation on this topic at the Ontario Golf Superintendents Conference. This presentation looks at nutrient availability, specifically at how we can ensure the grass is supplied with enough nutrients while at the same time ensuring that excess nutrients are not being applied. This involves an integrated look at plant use of nutrients, at fertilizer application, at soil nutrient levels, and leaf nutrient content. Healthy turfgrass plants are the goal, and those plants have a known concentration of nutrients in the leaves. By estimating the amount of nutrients that are harvested when the leaves are cut, and relating that to the amount of nutrients in the soil, one can make an informed judgement on whether or not an element is required as fertilizer, and if so, just how much is required.

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- Estimating Turfgrass Nutrient Use Micah Woods Chief Scientist | Asian Turfgrass Center seminar.asianturfgrass.com/20150128_ontario.html @asianturfgrass Ontario GSA Conference Niagara Falls 28 January 2015
- First, do we need to add an element as fertilizer? seashore paspalum Lanai, Hawaii
- Second, how much do we need to add? creeping bentgrass Hokkaido, Japan
- To answer those fundamental questions, we need to estimate 3 quantities creeping bentgrass Shanghai, China
- To answer those fundamental questions, we need to estimate 3 quantities creeping bentgrass Shanghai, China
- To answer those fundamental questions, we need to estimate 3 quantities creeping bentgrass Shanghai, China
- These 3 quantities simplify to 2 – the amount we have, and the amount we need The amount the grass uses + the amount required (a + b) is the amount we need The amount in the soil (c) is the amount we have manilagrass (Zoysia matrella) Chonburi, Thailand
- If the amount we have is more than the amount we need, none of that element is required as fertilizer. If the amount we have is smaller than the amount we need, fertilizer must be supplied to make up the difference. a + b - c seashore paspalum Mauritius
- Quantity a, the amount used We can make a conservative estimate of this based on nitrogen applied and turfgrass species.
- 1) the more nitrogen applied, the more growth & 2) we always want healthy grass creeping bentgrass Chiba, Japan
- Bentgrass leaves contain, as % of dry weight, about: N 4% K 2% P 0.5% Ca 0.5% Mg 0.2% S 0.2% Fe 0.01% creeping bentgrass Hokkaido, Japan
- To estimate the amount used: 1. Known N supply 2. (N supply) / 0.04 = dry clipping yield 3. From that, use of any element can be estimated
- Quantity b, the amount required in soil We identify this as the lowest level we can safely let the element decrease to in the soil. This is the basis of the minimum levels for sustainable nutrition (MLSN).
- http://www.paceturf.org/PTRI/Documents/1202_ref.pdf
- Quantity c, the amount in the soil We measure this by doing a soil test.
- How to work out a + b – c = fertilizer requirement First, Toronto as an example
- Using growth potential (GP) allows one to get an estimate of the amount of nitrogen that may be used, based on optimum growth temperatures and desired growth rate. For creeping bentgrass, I generally use a monthly maximum of 3 g N/m2 .
- These values of predicted use are quantity a
- Useful conversion factors 5 g/m2 = 1 lb/1000 f2 1 g/m2 = 6.7 ppm in a 10 cm rootzone with bulk density of 1.5
- http://www.paceturf.org/index.php/public/ipm_planning_tools
- element MLSN (ppm) MLSN (g/m2 ) K 37 5.5 P 21 3.1 Ca 331 49 Mg 47 7.0 S 7 1.0 Quantity b, the amount required in the soil, we can take from the MLSN guidelines.
- element M3 (ppm) M3 (g/m2 ) K 67 10 P 74 11 Ca 605 90 Mg 87 13 S 14 2.1 Quantity c, the amount we have in the soil, we measure by a soil test. I'll use here median values from Global Soil Survey samples (n = 93).
- The amount of an element required as fertilizer is the amount we need minus the amount we have: a + b – c For the conditions described, using GP for Toronto 2014 weather, maximum monthly N of 3 g/m2 , and soil data as the median of the GSS, we get .
- element a (use) b (reserve) c (in soil) fertilizer K 6.6 5.5 10 2.1 P 1.7 3.1 11 -6.2 Ca 1.7 49 90 -39 Mg 0.7 7.0 13 -5.3 S 0.7 1.0 2.1 -0.4
- This answers the 2 questions we started with. Is an element required as fertilizer? If so, how much? In the process of answering, we also familiarize ourselves with the useful quantities a, b, and c. creeping bentgrass Shimane, Japan
- https://www.facebook.com/mlsnturfhttp://www.blog.asianturfgrass.com/fertilizer/ http://www.paceturf.org/journal/global_soil_survey http://www.paceturf.org/journal/minimum_level_for_sustainable_nutrition
- Handout link seminar.asianturfgrass.com/20150128_ontario.html

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