March 25th

Hi All,

After a pretty nice week with some warm dry days and mild nights, you can see the countryside changing in front of you as the tram lines in crops deepen, hedgerows push into leaf and blossom and the first of our summer migrants makes landfall. Lots of birds of prey out and about yesterday on the thermals and I’m seeing / hearing a lot more Ravens as well, so they’re making a comeback. I remember clinging to a mountain ridge in Arran (Cir Mhor) during a white out in mid-winter and watching 2 Ravens dancing on the wind in front of me, totally oblivious to my predicament.

I heard a ChiffChaff yesterday (Summer migrant warbler) and on Saturday whilst enduring a very, very  frustrating session of fly fishing, I heard the first chatter of Sandmartins above me. There was a huge buzzer (midge) hatch on the water and you could almost sense their happiness at arriving from their long haul up from Africa (just think about that) and having a full plate of dinner on the table !! :).

It always makes me wonder how on earth a small bird like a Sand Martin or a Swallow manages to navigate the 6,000 odd miles from South Africa across Africa, the Sahara desert and then Europe before hopping across the channel / Irish Sea to arrive at the same location they left some 6 months earlier. In my childhood days, that was an outside loo in Leicestershire for our Swallows and they’re still visiting to this day. (Not the most luxurious of locations I’d admit!). Anyway it’s great to hear their chatter and looking forward to this week, they’ll find plenty of insects on the wing because high pressure will be in charge and that means warm days (particularly the 2nd part of the week) but chilly nights…

General Weather Situation

Quite a straight-forward weather blog this week because we have such a stable weather situation with the only real difference in the weather you experience down to cloud cover from Monday to Thursday. The two Meteoturf images above illustrate the differences between the north and Scotland which will have plenty of cloud cover this week and less sun hours vs. Ireland, Wales and England which will have much clearer skies through the day and night. So you can see for Scotland, the duller outlook for this week means mild night time temperatures but cooler days with the maximum temperature in low double figures accompanied by a north-westerly / westerly wind.

For England, Wales and Ireland we see the typical spring dichotomy of warm days and cool nights, with the coldest nights reserved for the start of the week with a likely ground frost on Tuesday morning before day and night temperatures rise during the 2nd half of the week.

So dependent on your location, you’ll see either warm days and cold nights with the warmth increasing for the 2nd part of the week or more in the way of cloud cover, milder nights and dull, cooler days, but we look dry for the 2nd week in a row (as predicted 2 weeks ago ahahaha)

Winds will be all over the place this week for Ireland and Wales with southerly, veering to northerly and anything in-between. For Scotland you’ll pick up the westerly part of the high and for England it looks like mainly north-westerly winds till later in the week.

So I’ll pick things up from Friday when we see a weak rain front push into north-west Scotland accompanied by thick cloud. This will push into central areas of Scotland through the 2nd part of Friday to bring light rain for the 2nd half of the day here. Further south and west Friday should represent the warmest day of the week with south-westerly winds and plenty of sunshine once that cloud cover has broken up, so mid-teen temperatures likely for Ireland, England and Wales. The weak weather front over Scotland will also push cloud cover south overnight into Saturday across the U.K and Ireland so it is highly likely that Saturday may dawn cloudier for the north of England and Midlands before the sun breaks through across most areas to give a lovely Saturday with mild temperatures into the mid-teens and a nice westerly / southerly wind. Further west and north across Ireland, a cool northerly / north-westerly wind will peg those temperatures back into low double figures, but out of the wind it’ll still feel pleasant.  Later on Saturday we see the wind swing round to the east and that’ll really introduce a much cooler feel to conditions on Sunday with more cloud cover especially for the southern half of the U.K and lower temperature just breaking into double figures.

Weather Outlook

The change in the wind direction at the weekend is the signal that the grip of high pressure will begin to loosen for the start of next week and that could (I say could) herald the arrival of more unsettled conditions during the week. So next week looks like starting off how the weekend finished, on the cool side, but dry and with plenty of sunshine across the south. Cloud will push in from the north through Tuesday and then we will see rain coming in to the north and west for the 2nd part of Tuesday before this pushes further south into all areas from Wednesday. On the cool side as well with a north-westerly air stream that will pull in blustery showers, some of them wintry over elevation I think, for the 2nd half of next week. It has to be said that the frontal system causing this change in the weather doesn’t look really strong so it may change as we go through the week in terms of rainfall and temperature, we will see. By that time we will be needing this rain.

Agronomic Note

Seeing out March…

By next Monday we will be into the 1st day of April (so tempting) so I’ll continue the growth monitoring theme through till the end of next month. The image above is for my local Northampton location but the weather patterns hold pretty true for England, Wales and Ireland again (Scotland’s and the north of England has been wetter and colder). You can see the dry spells which will mark this winter out as below-average rainfall for The Midlands and the consistent growth through the latter part of February and March. Now a daily G.P of 0.3 (equivalent to a GDD of just over 3) isn’t anything to shout about growth-wise, it is steady clip, but nothing drastic, no growth flush and in essence is probably better for the plant itself. At higher temperatures (and particularly with high available N), the plant will prioritise shoot  over root growth, (Growth Partitioning) but at the sort of numbers shown above, this shouldn’t be happening. (unless of course you’ve shoved 40kg of N on :)).

Shallow rooted Poa annua 🙂

It may pay us well to remember that it is root growth that functions as our insurance policy when we get to dry spells of weather like we are seeing currently. Dry spells in the spring usually only desiccate the surface 10-20mm and with good rooting will be no problem to the grass plant, though surface roots may suffer a little.

That said, the daily E.T is starting to ramp up and the projected moisture loss for this week in my location is 10mm, not inconsiderable for the end of March. Even though moisture meters are great for keeping a track on your soil moisture status (and as such usually result in less irrigation being applied), it is likely that desiccation will be occurring above the depth that a normal probe reads (50-60mm) so best to keep an eye on things when you change holes or take a soil profile. It will of course be particularly important for areas that were either over-seeded last autumn or dormant seeded this winter (which in general have done very well because of good early soil temperatures and moisture) where the new seed has a formative root system and is particularly sensitive to desiccation.

Nutrient input…

There was a question on Twitter (thanks Jon) about potassium inputs and whether there would be a difference in soil levels of K if 50kg of K2O were applied over a season in foliar or granular form and what would this difference be ?

To my way of thinking there are numerous variables associated with this question but some factors will impact on the end result more than others. The ability of the soil to retain nutrients is denoted by the CEC of the rootzone (Cation-exchange capacity). This is a measure of how many negative sites exist in your soil matrix onto which positively charged nutrient ions (cations) can bind (and be more resistant to loss through leaching). So we are talking calcium (Ca), magnesium (Mg), potassium (K), hydrogen (H), etc ions binding to negatively charged sites (typically represented by clay and organic matter).

Now if you have a low CEC rootzone, say 2.0-4.0 meq ( typically a USGA-spec golf green or a high sand content rootzone sportspitch), this type of rootzone will have a poor capacity to retain cations like potassium. If you input a high level in soluble form (> 20-25kg / K2O / Ha for example), only a small amount will be retained in the rootzone, the rest would either be taken up by the plant or leached, particularly if weather conditions were cool (slow growth=slow uptake) and there was plenty of rainfall. So there is a finite holding capacity to applied nutrient (in this case K) in your rootzone and there is also competition between nutrients for retention on these sites.

For example, if you are managing a calcareous rootzone, the majority of sites will already be occupied by calcium and so a calcareous sand rootzone (like we have on many  golf courses, sports pitches in Ireland) offers precious little retention for applied cations like potassium.

The next variable is the form of applied K

Now liquid applications of potassium are always going to be soluble in nature (kind of goes with the territory) and so these are the most sensitive to leaching, first off the leaf surface and then into the rootzone. The trade-off is that we typically do not need to apply high levels of potassium in foliar form because we know uptake of foliar nutrients is relatively inefficient. So any surplus the plant doesn’t absorb will be washed into the rootzone and then we are back where we started, i.e dependent on the nutrient retention of the rootzone. Granular applications of nutrient can also be in soluble form (potassium sulphate, potassium nitrate, e.t.c) but they can also be in slow release, organic or controlled release form. The latter limit the release of K to the rootzone (and hence the plant) , are less sensitive to leaching and so make sense to use in low CEC – high leaching potential scenarios.

I remember tangling horns with an agronomist from the U.S once who recommended applying straight potassium sulphate granular (0-0-50) at 20gms/m2 on a monthly basis to a relatively new USGA-spec rootzone. So that’s 100kg / K2O/ ha / per application. The rootzone was high sand, low CEC and not surprisingly at the end of the season had no more retained potassium than a ‘control green’ to which only 150kg / K2O / ha / year had been applied. The surplus K that wasn’t retained in the rootzone or taken up by the plant was leached. There was no significant difference in plant tissue K levels.

So the question was….If I applied 50kg / Ha of K granular vs. 50kg / Ha of K foliar only, what would be the difference in ppm in a soil test over a certain duration ?

My answer would be that the granular input would result in a higher soil ppm figure but that figure would be wholely-dependent on the CEC of the rootzone. The foliar input would I think always result in a lower soil ppm figure because you’d be applying smaller amounts and therefore less would reach the soil matrix. What would be the difference in ppm between the two systems ? well tricky to say because to answer that we’d need to understand the CEC and the form of applied K. So I don’t think there’s a ‘clear number’ because of the other variables involved, but one system would input more soil K than the other.

For me applying potassium should be in line with the requirements of the grass plant (typically 2.0-3.0% K in leaf tissue) and whether the plant obtains this from a direct foliar application or from a soil application isn’t the most important thing. In practice most end-users apply potassium in a mixture of granular and liquid forms and I like to use the former during periods of the season when we are more sensitive to leaching losses (cool and wet periods like the winter) and typically to apply in slow release or controlled release form.

Once last thing, a wise old owl back in my formative years commented to me that grass doesn’t grow on a piece of paper. In this day and age where information is everywhere and everything, it’s worth remembering that we are dealing with nature and along with it, a multitude of variables, so I take numbers as a guide not gospel when it comes to this sort of thing.

OK that’s a wrap for another week, have to go and see another man about a dog 🙁

Enjoy the sun and the nice temperatures this week and let’s hope there’s some rain on the forecast when I sit down to type this next week 🙂

All the best.

Mark Hunt