Get the most from early spring nitrogen

Get the most from early spring nitrogen

1 August 2021

Getting the best response from nitrogen (N) fertiliser is more important than ever, and sulphur (S) is part of the solution.

To thrive, pasture likes to take up a particular ratio of N and S, but S is often lacking in early spring following winter’s wet and cold conditions.

If sulphate S (the only form of S plants can use) is low, at the time when N fertiliser is applied, the pasture’s response rate (kg DM/ha per kg N/ha) to N will be lower. Clovers will particularly suffer if sulphate S is low, further impacting the supply of N to other pasture species.

Why is suplhate S low in spring?

Plant available sulphate S is highly soluble, and like N, leaches over winter (but is not known to cause any environmental issues).

Production of sulphate S also declines over winter due to decreased bacterial activity in cold soil. Bacteria in the soil are responsible for converting other forms of S – organic S (found in the soil) and elemental S (provided by fertiliser) – into sulphate S are less active over winter, and conversion slows down.

By late winter and early spring, leaching and a slowdown in conversion takes their toll, often resulting in a short supply of sulphate S for the pasture, and posing a particular problem for application of N in spring.

Identifying and overcoming deficiencies

Sulphur is relatively cheap and straight-forward to apply with other nutrients and overcoming early spring S deficiencies ensures spring pasture can take up N and flourish.

Spring herbage testing can be used to complement soil testing when deciding if S is required for a good pasture response to N application’s (see Table 1).

If an N and S combination is required, two good options are the SustaiN Ammo range and Phased N Quick Start.

SustaiN Ammo products support pasture growth by providing the required ratio of N and S, with the S content as sulphate S readily available for plant uptake. The inclusion of SustaiN reduces the amount of N lost as ammonia gas and increases N efficiency. The SustaiN also allows more flexibility in timing of application, as it does not need 10 mm or more of rain or irrigation water within 8 hours (post application) to reduce the losses as ammonia gas.

On soils prone to S leaching, such as pumice, podzols, organic and South Island Recent, PhaSedN Quick Start is a good late winter to early spring option to address short and medium-to-long term S needs. It combines PhaSedN with sulphate of ammonia and provides both elemental and sulphate S with N (see Table 2).

Article supplied by Ballance Agri-Nutrients.