THE RIGHT N FERTILIZER

Many farms in Western Canada rely on anhydrous ammonia (NH3) fertilizer as the main source of nitrogen for their crops. Nutrien Ag Solutions supplies growers with NH3 from many of our locations, primarily in the northern Prairies. For NH3 to be a good choice of crop nutrition for a farm, it needs to fit within the parameters of 4R Nutrient Stewardship agronomy – the Right fertilizer applied at the Right rate, at the Right time and at the Right place in the soil. 

PLACEMENT

In the spring, we should be thinking about the Right placement of NH3 in the soil.

Consider that NH3 must be placed in a band beneath the soil – that’s the Right place for any nitrogen fertilizer to avoid loss as a gas or leaching and to protect the nitrogen from ‘immobilization’ by bacteria as last year’s crop residue decays.

[106 site years of data in Western Canada. Rennie, Doyle and Cowell, 1993:  Summary of western Canadian research.]

DEPTH

There have been numerous studies to measure depth and movement of NH3 in Western Canada, including the research of Les Henry and Terry Hogg which measured NH3 movement behind farm applicators at rates of 35 to 150 lb N per acre. This study and others determined that nearly all NH3 is contained within a 5 cm radius from the centre of the application band.

[Ammonium (NH4+) levels in field soils at 7 sites in the Black soil zone in radius of an NH3 band (Les Henry and Terry Hogg, Can. J. Soil Sci., 1982).]

Further work with soil cores by Les Henry and Dale Tomasiewicz confirmed that NH3 bands are contained in soil in a narrow radius in both wet and dry soils.

We don’t need to apply NH3 very deep, which is sometimes assumed. For most soils, an application depth of 8-10 cm is enough to prevent loss. Common sense must prevail when selecting a depth to set an NH3 applicator. The soil clay and organic matter will very quickly trap and retain applied NH3, but you still need good soil conditions and closure behind each bander. 

NH3 can be a 4R fertilizer for your farm: the Right fertilizer applied at the Right Rate and Right Time – and the Right depth.

Sulphur (S) is considered to be the fourth major nutrient required by plants. It is often forgotten in the fertility program, yet most crops utilize as much S as phosphorus. Critical to growth, S plays a major role in the formation of proteins, enzymes, chlorophyll and effective nodulation.

CROP SYMPTOMS

Typically, S deficient crops are spindly, later maturing and the younger leaves are pale green to yellow in colour. In canola, the leaves may cup inwards and develop a reddish or pink colouration on the underside of the leaf.

SULPHUR DEFICIENT SOILS

Generally, S deficiencies occur on soils that are coarse textured (sandy), well drained and/or low in organic matter. Deficiencies are also noted on soils with a relatively long history of canola or alfalfa production in the rotation.

N:S BALANCE

Depending on the crop and its growth stage, optimal nitrogen (N) to sulphur (N:S) ratios range between 7:1 and 15:1. To obtain the optimal plant N:S ratios, soil N:S ratios should be between 5:1 and 10:1, depending upon the crop grown. The ratio in the soil should always be lower than that required by the plant to ensure adequate N:S ratios in the plant.

A soil and plant tissue analysis will help identify the need for additional S and the rate required. When soil testing information is not available and the soil is thought to be marginally deficient in S, N and S should be added in a ratio of 7:1 for canola and 10:1 for wheat.

FORMS OF SULPHUR

Plants take up S in the sulphate form (SO4=). Ammonium sulphate supplies a readily available form of sulphate. The elemental form of S must be oxidized to the sulphate form before it is available to the crop. As a result, spring applied elemental S may not supply adequate sulphate to your crop during the growing period in which it is required.

General fertilizer recommendations  

APPLICATION METHOD

Sulphate-S can be applied pre-plant (broadcast, banded or seed row), topdressed after crop emergence or at seeding.