Soil temperature

You’ll find more information, advice and guidance on soil temperature, grassland management and optimum times for applying fertiliser on our Soil and Grassland Blog.

Data for the Soil Temperature Map is provided by Natural Resources Wales. Data is collected daily and the map is updated every morning.


As the weather looks set to improve, there are a few people starting to think about fertilising – albeit probably a month later than usual for some. Here are a few issues to consider.

 

9 March 2020

 

Written by - Chris Duller Soil and Grassland Advisor

 

Soil temperatures have barely dipped below 4 o C all winter in most places in Wales, and they are currently hovering around  6 o C for many (check out the Farming Connect Soil Temperature Map).

Soil temperatures are crucial for the recovery of applied nitrogen. For every 1 o C increase, you can increase nitrogen recovery by around 5%. Wet, heavy soils will tend to stay colder for longer, as will north facing banks, so those are the fields to hold back from fertilising.

For many, the whole story about soil temperature is irrelevant, it’s all about ground conditions and soil water levels. There is no point in fertilising early and making a mess of fields. With many soils saturated, it will only take a small amount of rainfall for nitrates to quickly move to field drains and be lost.

For the next couple of weeks, it will be a case of getting to the driest fields, or parts of fields, as and when conditions allow. Try using small tractors, with twin wheels, to avoid making ruts. You can even use quad-mounted spreaders. Remember, it only takes 5 minutes to make a mess, but it will take a year or more for soils to recover.

With high soil water status, it is important to think about your choice of product to try and minimise losses. It’s also important to use the appropriate application rates.

Urea would be the logical choice to use during cold, wet conditions. But you need to be careful as air temperatures above 12 o C start to accelerate ammonia loss from urea, especially in windy conditions. The first 12 hours after application are key to ammonia loss, so if things start to warm up then you should be thinking about afternoon and evening applications. A project on Rhiwaedog Farm, a Farming Connect Demonstration Site, looks at using protected urea to compare nitrogen recovery with conventional urea and Ammonium Nitrate (AN), so keep an eye out for the results.

We know that sulphur plays a key role in nitrogen recovery, therefore, it would make sense to use sulphur products this spring. The recommendation for grazing ground is 20-30kg/ha of sulphur for every 100kg/ha of nitrogen applied, so products with 7-9 % sulphur would be ideal. For silage fields it is recommended that you apply 40kg/ha of sulphur for every cut, therefore a slightly higher sulphur content may be needed, such as 27:0:0:12. 

Application rates are all about risk management. If it’s a dry field that is full of ryegrass and growing well, and the forecast for the week isn’t bad, then rates can go up. If it’s staying cold and showery, I’d be erring on the side of caution and probably keep nitrogen rates below 30 units/acre (37kgN/ha).

Key message: Every field on a farm is different. Avoid going too early on the risky ones, and definitely don’t make a mess.