Pea yields climbed by an average of just over 9% across 12 Saskatchewan site-years when phosphate fertilizer was side-banded, according to Agriculture Applied Research Management (Agri-ARM) trials led by the Indian Head Agricultural Research Foundation (IHARF).

The work, funded by Saskatchewan Pulse Growers (2019-2020) and later by the province's Agriculture and Demonstration of Practices and Technologies (ADOPT) program in 2025, set out to settle two field questions: how much phosphate field pea actually needs, and where to place it.

What rate of P pays?

The 2019-2020 study ran at six Agri-ARM sites: Swift Current, Outlook, Scott, Indian Head, Yorkton and Melfort. Fifteen treatments compared nitrogen, phosphorus, potassium and sulphur fertility.

For phosphorus, four side-banded rates went in the ground: 18, 36, 53 and 71 lb P2O5/ac (20, 40, 60, 80 kg/ha). Soil test P across sites was generally low at 3 to 12 ppm Olsen-P, with one Outlook 2019 site at 24 ppm.

Yield response to P followed a quadratic curve. Yield levelled off at roughly 66 bu/ac (4.44 t/ha) when P was applied in the 40 to 50 lb P2O5/ac range (45 to 56 kg/ha).

"The economic optimum was closer to 40 lb/ac, perhaps a bit less at today's prices," says Chris Holzapfel, IHARF research manager and lead author.

Does soil testing actually pay?

Holzapfel recorded statistically significant responses (95% probability) at 64% of the low-P sites, or 7 of 11. At the 90% probability threshold, the hit rate climbed to 82%.

Outlook offers the clearest case. In 2019, with a 5 ppm Olsen-P test, pea yield rose linearly with rising P rate. In 2020, after soil test P reached 24 ppm, the response disappeared.

Which P product and placement wins?

The 2025 ADOPT study moved the question to product form and placement. Four Agri-ARM sites ran the work: Melfort, Scott, Swift Current and Indian Head. Five products went side-banded or seed-placed at 40 lb P2O5/ac (45 kg/ha):

• Mono-ammonium phosphate (MAP; 11-52-0)
• MAP plus ammonium sulphate (MAP+AMS; 21-0-0-24)
• MicroEssentials S15 (MES15; 13-33-0-15)
• MAP plus MST (9-43-0-16)
• Crystal Green Synchro 50 (9-42.5-0-0 plus 7 Mg)

MAP+MST pairs MAP with micronized elemental sulphur. Synchro 50 homogenises MAP and struvite inside each granule rather than blending them as a 50:50 mix.

Side-banding was the safest and most effective placement for every product tested. Seedling injury with seed placement varied by site and formulation.

Where did placement bite?

At Indian Head and Melfort, fertilizer form and placement did not affect plant density. At Swift Current, every product except MAP+MST cut emergence significantly relative to its side-banded counterpart, with MAP+AMS and MES15 doing the most damage.

Seedling injury tracked soil texture. Coarser, lower-organic-matter soils suffered more, in order: Swift Current, Scott, Melfort, Indian Head.

Yield responses to P varied by site:

• Indian Head (14 ppm Olsen-P): non-significant 3% lift, yields of 82 to 88 bu/ac (5.5 to 5.9 t/ha) across forms and placements
• Melfort (14 ppm Olsen-P): insignificant 5% lift between treatments
• Swift Current (13 ppm Olsen-P): 10% lift over the control, no significant placement difference; MAP+AMS produced the highest yields on average

Protein held steady at Indian Head, Melfort or Scott. Seed-placed fertilizer cut protein at Swift Current, particularly MES15. Holzapfel flags high residual nitrate-N and greater fertilizer injury as possible causes.

What changes on the farm?

"Overall, our results highlight the importance of P fertilizer for achieving high field pea yields. Side-banding the preferred placement option where possible, performing equal to or better than seed-placed P in essentially all cases," Holzapfel says.

He adds that growers did not see significant yield benefits from any novel P form compared with MAP alone. Novel products may still fit specific needs. MES15 or MAP+MST work as sulphur carriers for growers moving away from AMS. Synchro 50 or MAP/struvite blends suit growers who must seed-place high P rates without crop injury.

Holzapfel launched a follow-up in 2026 that adds Top-Phos to the product list. He plans to repeat the trial in 2027.