Enhanced Phosphorus Uptake in Flax

Objective

1. Does flax uptake of P and the corresponding seed yield response vary with the specific P fertilizer formulation that is used, and does this response differ with environment and/or soil qualities?
2. How do biological inoculants intended to improve P solubility or arbuscular mycorrhizal fungi affect P uptake and seed yield in flax when used alone or combined with different formulations of P fertilizer
3. Does the combination of P fertilizer and biological inoculants intended to enhance P solubility and/or uptake improve P uptake and seed yield and flax to a greater extent than either of these products applied on their own?
4. Does flax response to different P fertilizer formulations and/or biological inoculants intended to enhance P solubility and/or uptake differ depending on soil qualities (i.e., pH, residual P levels) or environment (i.e., soil climatic zone and weather)

Project Description

Although flax (Linum usitatissimum) has been shown to respond modestly to phosphorus (P) fertilizer applications, the response can be unpredictable and is often less pronounced than for other crops commonly grown in Saskatchewan. That said, flax does have relatively high P requirements with a 2200 kg/ha crop (35 bu/ac) removing approximately 28 kg P₂O₅/ha in the seed and total uptake likely being as high as 35 kg P₂O₅/ha.

Although monoammonium phosphate (11-52-0) has long been considered the standard with respect to granular P fertilizer options in western Canada, other formulations are available. While not exclusively a P product, MicroEssentials® S15 (13-33-0-15) is a multi-nutrient fertilizer which has the benefits of improved seed-safety (relative to MAP/AMS blends) and providing slow release sulfur with the S consisting of equal parts sulfate and elemental forms. Promotional material for S15 from Mosaic showed significantly higher canola plant populations and a 2.6 bu/ac yield advantage (average of 24 trials over a three-year period) over MAP plus ammonium sulphate (AMS) blends. For wheat, when averaged over 39 sites throughout the U.S. and Canada, Mosaic (2019) reported a more modest 1.6 bu/ac advantage over MAP + AMS, equating to a 23% versus 20% yield increase over the control for S15 versus the MAP/AMS blend. Independent University of Manitoba research with canola showed improved seed safety over MAP/AMS but also warned that S15 may not be as effective for providing plant available S as sulfate based products (i.e. MAP/AMS blends). That aside, the claim specific to P is that the combination of nutrients in S15 creates a more acidic environment which helps keep the P in plant available, soluble forms for longer; thus, leading to better overall uptake. Because it is a relatively new product, publicly available information on crop response to MAP + MST® is very limited. The nutrient analysis for this product is 9-43-0-16 and it is essentially MAP with micronized elemental sulfur particles (average particle size of 15 microns) distributed uniformly throughout each granule. While this formulation is largely marketed as an improved option for delivering elemental S to crops, similar to MicroEssentials® formulations, the solubility and crop uptake of P with MAP + MST® may be enhanced relative to MAP due to the acidifying effect of the elemental S. While third-party research looking at the relative uptake and yield response to P is extremely limited for MAP + MST®, preliminary results from the Discovery Research Farm near Langham, Saskatchewan show favorable crop responses to this product and enhanced solubility. As of 2023, MAP accounted for 66% of the P market in western Canada while MicoEssentials® and MAP + MST® formulations accounted for approximately 14% and 2% of the P market by volume, respectively. Importantly, MAP + MST® is a much newer product than MicroEssentials® formulations and it is likely that its market share could increase in years to come.

Flax is dependent on arbuscular mycorrhizal fungi (AMF) for uptake of immobile nutrients (like P) and, as such, high frequencies of canola in the rotation and/or conventional tillage systems can have a negative impact on its productivity. With this in mind, flax may be a particularly good candidate for biological inoculants that have potential to improve P uptake. Focusing on AMF, we know that many crops benefit greatly from their symbiotic relationship with plant roots and established AMF networks can effectively function as an extension of the crop’s root system.