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It’s important to understand the interrelationship of nitrogen (N) and sulphur (S) to maximise spring growth.
Nitrogen and sulphur are both important for spring pasture quality and quantity. Understanding how this nutrient double-act works will help you use your fertiliser inputs effectively and economically to make the most of the spring flush.
“Pasture plants contain around four to five percent nitrogen and 0.3-0.4 percent sulphur, roughly a twelve to one (12:1) ratio,” explains Murray Lane, Forage Specialist with Ballance Agri-Nutrients. “This means they like to take up these nutrients in a similar ratio, so the levels of plant-available sulphur in your soil may limit nitrogen uptake if sulphur is low.”
A sulphur-limited nitrogen response is much more likely to occur in spring than autumn. This is a result of soluble sulphate leaching from soil in wet winter conditions, combined with cool soil temperatures which slow down the action of microbes that convert organic sulphur into plant-available sulphate.
This may result in pastures being temporarily deficient in sulphur in early spring, as plant demand outstrips soil supply. If soil sulphur levels are too low (i.e. deficient relative to the crop/pasture requirement), this may limit the efficiency at which the pasture responds to fertiliser N. “A lack of sulphur could also limit clover growth as temperatures rise,” says Murray. “Clover is a comparatively poor competitor for sulphur. If sulphur supply affects clover growth this can alter the proportion of clover in your sward and the degree to which it can supply nitrogen to other pasture species.”
If you plan to put on maintenance PKS (phosphorus, potassium and sulphur) later in spring, only relatively small amounts of sulphur will be needed to supply enough for the early spring period. Sulphur needs, products and application rates should be considered in the context of your production and/or financial goals and overall nutrient management, based on a comprehensive soil testing programme and sound advice.
In spring, herbage testing can be used to complement soil testing when deciding on whether to use a straight nitrogen product or a nitrogen and sulphur combination.
If you need nitrogen alone, the common choices are urea or SustaiN. However, which product to choose depends on certain factors.
“Cool temperatures in early spring will not reduce your risk of nitrogen loss from ammonia volatilisation,” says Murray. “Five to 10 millimeters (mm) of rain or irrigation within eight hours of application is still required or SustaiN can be used to reduce your volatilisation risk by up to 50 percent.”
Where both nitrogen and sulphur is needed, Sulphate of Ammonia (SOA) often comes to mind. SOA contains 19.5 percent nitrogen and 22 percent sulphur. This is generally much more sulphur than necessary if you are applying superphosphate later in spring.
SustaiN Ammo combines nitrogen (as SustaiN) with SOA to provide immediately available sulphur along with nitrogen. Sustain Ammo 30N contains 13.7 percent sulphur and 30.0 percent nitrogen and SustaiN Ammo 36N contains nine percent sulphur and 35.4 percent nitrogen.
PhaSedN Quick Start combines SustaiN, SOA and elemental sulphur, delivering 17.0 percent sulphur (as both immediately available and slow-release (S) and 31.3 percent nitrogen. PhaSedN Quick Start is a good late-winter/early-spring option to address short and medium-to-long term sulphur needs on soils prone to sulphur leaching.
For more information talk to your local Fonterra Farm Source team or visit us in-store.
Article supplied by Ballance Agri-Nutrients