Much of the grass in Herefordshire, where I am based, suffered during the difficult weather conditions of 2018 and consequently producers should focus on optimising nutrition to restore both quality and yield potential to former levels, with K and S being essential in this process.
This season NKS fertilisers containing potash and sulphur alongside nitrogen could be particularly beneficial to farmers seeking to meet the specific requirements of intensive grassland production.
The region has particular requirements with regard to grassland nutrition together with a high proportion of dairy and beef farms reliant on high yields of quality forage to achieve optimum cost-efficiency of production.
Making full use of available grassland is essential and this means ensuring you have supplied sufficient crop available nutrients, so soil testing is an essential first step in working out the precise amounts of nutrient you need to apply.
In the intensive grassland systems prevalent in the area you really have to test each field for P, K Mg and pH at least every 3-4 years. This is even more important following the difficult conditions in 2018 and the damage caused to grassland.
The role of potassium
Potassium (K) is one of the main driving forces of grass yield and the element most removed from soil in high production systems, he says.
In all systems, this is an area that needs addressing but it's a particular problem in the increasingly popular multi-cut silage systems.
Potassium has many functions within the plant but its primary role is with water movement and retention. This firstly provides efficient movement of nutrients within the plant and secondly helps to maintain plant cell strength, which is key to supporting the growth from nitrogen applications.
If we can maintain good levels of potassium within the plant it will be able to better cope with periods of stress but in recent years, the variability of rainfall has been a key factor in potassium levels and subsequent grass yield.
In Herefordshire, soil phosphorus levels are generally at target index 2 or above, whereas potassium index levels are predominantly below the target of 2.
This is due to two main factors. First, the soil's natural ability to hold on to potassium and second, the annual potassium off-take is not being balanced with application.
Why potash is essential in multi-cut systems
In a multi-cut system with four cuts you can expect a fresh weight yield of 54t/ha which translates roughly to a dry matter yield of 13.50 t/ha and this will result in an offtake of over 300kg/ha of potash.
With soil potash levels at index 1 this will require 360kg/ha to be applied each year and even at Target index 2- the requirement will still be 320kg/ha. At Index 2+ you will still need 200kg/ha to be applied every year to make up the shortfall. See table below.
If the RB209 (Nutrient Management Guide) recommendations are followed exactly, then the offtake amounts of potash will be fully replaced at index 2.
At index 1 we need to put more in to build soil reserves so it is important to match organic and bagged fertiliser potash inputs to optimise grass growth, because we know from Potash Development Association work that soil reserves and potash inputs both impact significantly on grass yield. See table below.
Manures contain valuable levels of both phosphate and potash and can have a positive impact on grassland nutrient management and help reduce fertiliser costs.
But you must test your manures pre-application as there are big variations in nutrient composition and this must be accurately accounted for before applying any additional nutrients.
Manures can have a vital role to play, but they must be managed efficiently and effectively and properly accounted for within the fertiliser plan.
Sulphur needs factoring in too
Sulphur is also an essential nutrient as it improves grass growth and overall Nitrogen Use Efficiency (NUE).
Sulphur is a major component of protein forming amino acids and is essential where there are higher amounts of applied nitrogen. The dramatic reduction in sulphur emissions over the last 20 years means there is now virtually nothing coming from the atmosphere to be available to plants.
When applying sulphur to grassland, levels have to be proportional to the amount of nitrogen used and the best way to determine these is to assess levels in the growing grass.
Ideally, sulphur levels need to be above 0.25% or the nitrogen to sulphur ratio needs to be below 13:1.
The challenge is that sulphur behaves very much like nitrogen and leaches from the soil system and so applications have to be made every year throughout the season.
Without the correct level of sulphur applied your yields will also be down and you'll struggle to achieve the required amount of crude protein in your silage.
Unlike phosphorus and potassium, ruminant manures do not contain much sulphur and what is there is largely unavailable for plant use, so you can't rely on manure to provide your grass crops with the sulphur they need.
Key points to remember
Potash
Closely monitor potassium levels and inputs in the following situations:
- Drought conditions will cause a lower availability of nutrient.
- Low pH as this leads to a low availability of all nutrients. ·
- Light soils will have a low nutrient holding capacity and more influenced by high rainfall.
- High magnesium index soil.
Sulphur
Sulphur inputs need to be closely monitored in the following situations:
- Light/medium or low organic matter soils as these cannot hold on to adequate sulphur. ·
- Areas of higher rainfall leading to higher chances of leaching.
- Higher application rates of nitrogen need a higher amount of sulphur in the right ratio.
For advice on nutrition programmes contact your local Frontier advisor or email This email address is being protected from spambots. You need JavaScript enabled to view it.
Finley Hawkins
Southern Fertiliser Business Development Manager
