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  • Writer's pictureMark Hunt

February 27th, 2023

Hi All,


Well this week sees us say goodbye to February and welcome in March, not that you'd know from a weather perspective. The first of March is the start of meteorological spring which is compromised of March, April and May as a season.


The more realistic (I think) start of spring is the Spring Equinox, which takes place on March 20th and marks the point where the sun crosses an imaginary line (called the Celestial Equinox) above the equator moving from the southern hemisphere to the northern hemisphere. On this date, day and night length are roughly equal It also marks the point in time when the northern hemisphere is heading towards summer whereas for the southern hemisphere, they are moving into autumn.


This year I think spring is going to keep us waiting with a pretty dull and cool start to the month as you'll read about below.



Whilst I am on the subject of the sun (tenuous link alert), I was reading today how the Northern Lights have been visible across the U.K last night and even down as far south as Norfolk and Essex. Apparently it is due to a strong Solar Flare and may be a feature of this week so if you're in an area of low light pollution and have insomnia, it might be a great way to pass the time😊


I have seen the Northern Lights twice from these shores, once whilst on the M74 travelling up to Scotland late at night when everyone pulled over onto the hard shoulder just to marvel and also in The Fens whilst fishing at night. I'd love to go to somewhere like Iceland to see it though....one for my bucket list of life.



General Weather Situation - w/c 27th February, 2023


As you'll see from the animated GIF's above courtesy of www.tropicaltidbits.com, we have a very stable weather pattern this week with high pressure in charge. The position of the high pressure off the north of Scotland means that the predominant wind direction will be north easterly for the southern half of the U.K, south easterly / easterly for Ireland and Scotland will be bereft of wind with perhaps a touch of easterly.

In the northern hemisphere, the winds associated with a high pressure systems rotate clockwise and so you can see from the image above, why it leads to a predominantly north easterly wind for the southern half of the U.K. Now a feature of north easterly winds is their ability to pull showers in off The Wash. At this point I have to sorry to my good friend Steg because I told him this week would be dry and he's probably chucking some expletives my way as I type this, whilst dodging those showers :) In my defence, they are few and far between today and short-lasting, but they straddle the length of the eastern coastline of the U.K currently and some are already pushing into Wales. So today's forecast is cold with a chilly north easterly wind and some sharp wintry showers thrown in to boot. Ireland will miss these entirely during daylight hours I think, but for all of us 7-8°C is the order of the day temperature-wise, with a cool wind chill on eastern coasts.


Now that's pretty much the forecast for the week really, such is the dominance of the high pressure with the exception that there should be more in the way of sunshine from Tuesday onwards and less of the showers. A strong north easterly wind will keep those daytime temperatures pinned below average for the start of March in the 7-9°C region. We will also have some chilly nights hovering around 1-2°C and whether you get ground frost will be completely dictated by overnight cloud cover. On Friday night for example, we went into the night with clear skies and the temperature quickly dropped to -1.7°C, but by the morning we were +4°C and frost-free as cloud cover had pushed in from The North Sea.


So, a pretty set week meteorologically-speaking and the weekend looks to be similar, but I think lighter winds are likely. So cool, mainly dry and frost is again a threat but wholly dependent on cloud cover. Since rainfall, wind strength and cloud cover are the 3 least forecastable weather parameters, I'm not even going to try :)


Weather Outlook - w/c 6th March, 2023


Perhaps the most interesting weather feature is what may potentially happen as we move more into March with the no / yes effects from the Sudden Stratospheric Warming Event that occurred recently.


Now first up I have to add a plethora of caveats because when you look at the GFS projections beyond 5-7 days, they are still changing daily. The projections alternate between easterlies continuing to dominate and a low pressure breakdown from the west. To give you an idea of the difference these two scenario's make to next week's forecast, here's the GFS and ECMWF forecast projections for the same day, Thursday, 9th March.

Now you might be sitting here reading this and thinking, what has this got to do with turfgrass management ?


Well for example, if the GFS output turns out to be correct, that will mean south west winds and rainfall I think, potentially the first significant rainfall since the middle of January for some locations. If the ECMWF projection wins the day, then that looks to me like extremely cold, south easterly - easterly winds and snow.


Some difference I think you'd agree.


What is clear in both scenarios is that the colder air in the east and north is likely to come into play in one form or another so I think we can say next week looks like starting off cold and mainly dry with northerly winds as that high pressure gets pushed north and west and then the winds slowly subside before we get to mid-week and the potential transition one way or another. To be honest I can't call it with any degree of certainty such is the variability between the forecasts, so I may do an update later this week if the signal becomes stronger either way as both scenarios have implications for turfgrass management.


Agronomic Notes


A cool temperature March is on the cards


Normally at this time of year I would be talking about the use of cool temperature granular fertilisation in January or February and its veritable merits, but the largely dry period of weather that began around the 16th of January put paid to any early in the year applications. If we take either of the weather projections for the first part of March, they have one thing in common I'd say and that is cooler than average temperatures.


Looking back over the last 18 years, we have experienced significant effects from SSW events in 2008, 2009, 2010, 2013 and 2018. Now some of these events occurred earlier in the year so by March their effects on the ground at our level may well have passed and are therefore less-discernible from a GDD perspective.


Below is a summary chart (thanks Sean for the historical data) of the total GDD dating back from 2005 at our default Thame, U.K location. I have highlighted in red, which years experienced a SSW event which affected weather in the stratosphere.


Now if we take a daily GDD total of 4 to be good growth (this would result for example from a spring day when we had 6°C at night and 14°C during the day) and multiply this by 31 (number of days in March), we have a total of 124 GDD. That would represent a really good month for spring growth. As you can see we have only had one of these (2017) since 2005. The average is more like 48 :(


How do we gear up agronomically for a low GDD March ?


Well, first up we have to manage expectations for those who use the calendar rather than reality as a yardstick. Communicating how many good growth days we have had per month or since the start of the year is a good starting point and that's why tracking GDD / G.P can be very useful. I first began getting interested in GDD back in 2010 when we had such a cold winter and people were asking how much behind growth was than 'normal' ?


How do you quantify that ?


Well, Growth-Degree-Days and latterly Growth Potential come into their own here....


Low temperature nutrition


This is a pretty straight forward subject but as pertinent to today's plant nutrition as it was when we first started applying fertiliser / nutrition to grass.


When soil temperature levels are low, microbial activity is also low and so conversion of some types of nutrients (more complex in structure, like urea as an example) is often very slow. Other nutrients require no conversion from microbial activity to be plant-available and this makes them entirely suitable for application during cold conditions whether they are applied as a granular or liquid fertiliser.


Some immediately-available nitrogen sources


Ammonium sulphate

Ammonium nitrate

Potassium nitrate

Calcium nitrate

Calcium ammonium nitrate

Magnesium nitrate


These nutrient forms are typically used in low-temperature available fertiliser formulations as all or a portion of the available N. As with anything, they have their negative side as well. Nitrate nitrogen for example, can easily be leached from a low nutrient-retention soil (high sand content), especially when conditions are cool and rainfall levels are high.


So for example, if you have a fertiliser with 50% of the nitrogen derived from ammonium sulphate and 50% from urea, you know half of the applied nitrogen will be immediately-available to the plant, half will be slowly available because it is dependent on microbial activity to break down the carbon-nitrogen structure of the urea and convert into a plant-available form. The same is true of organic nitrogen sources. In common with synthetic nitrogen, organic forms of nitrogen exist in fast and slowly-available forms. That is why in the old days, you used a mix of organic N sources, like Dried Blood, Hoof & Horn and the like. (I am showing my age here)


So dependent on how the GFS charts shape up for the middle of next week, I'd be getting myself prepped to apply the correct type of nutrition to meet the needs of the grass plant. This doesn't have to be huge amounts of N. Typically in a liquid application 4-6kg per hectare of cool-temperature N is sufficient to generate a grass response. If we look to be heading cool, wet and windy, then your low temperature-available granular fertilisers are the way to go because they are more resistant to leaching and provide better longevity during periods of high rainfall.


Ok, that's all for this week folks, wrap up well and let's see how the SSW event unfolds. If there's a clear signal at the end of the week one way or another, I'll try and squeeze in a mini blog.


All the best.


Mark Hunt

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