06 Jan Agronomy Update – Jan 6th
AIM Trial Report – Reduced Phosphorus:
Bethany and I are currently working on reports from 2024 trials. As they are finished, you can find links to those reports on the PEI Potato Agronomy site under “Reports”. One of the first ones that I would like to bring to your attention is a project we did looking at phosphorus (P) rate and whether there is justification for producers to reduce P rates in some situations.
Historically, PEI growers have had high P rates in their fertility programs. The reasons for this are logical: potatoes require phosphorus for quick root growth during early growth stages and P was historically less available in PEI soils due to cold spring soil temperatures and low pH that binds P to aluminum (Al). However, as P levels have built up in soil and pH levels have increased in many fields (as common scab becomes less of a concern for many varieties), many growers haven’t adjusted P levels in fertilizer blends. In addition, use of liquid P products at planting also makes P more available to the crop and reduces the need for high rates of P in the planter blend.
In 2024, we worked with two growers to reduce P2O5 rates in a total of 3 fields from their standard rate (150 or 160 lbs/ac P2O5) to 100 lbs/acre in fields with high soil test levels (> 400 ppm P2O5) and pH greater than 5.9. Soil chemistry tells us that P becomes much less bound by Al as pH increases into the 6s, hitting a peak availability at around pH 6.4. Both growers used fertilizer blends that only differed in P (N, K, micros all the same) and strips were planted side-by-side with the same varieties in each field. We then took harvest samples in the fall and graded at Cavendish Farms Central Grading. All three fields were Mountain Gem Russets.
We saw that there was no significant difference in yield or quality between low P and grower standard practice (GSP) across the three trials, and there was no significant difference in any individual trial either. In all three trials, the total and marketable yield was slightly higher in the Low P treatment, but the difference was small enough to be not statistically significant.
A reduction of 50 lbs/ac of P2O5 from a fertilizer blend using 2024 fertilizer prices would decrease the per acre fertilizer bill by ~$37/acre, assuming that DAP is the fertilizer of choice and that the N in DAP is replaced by urea. While this value will change depending on blends and pricing, it is not an insignificant opportunity for savings. On a 500 acre potato farm, this represents $18,650 in savings with no loss in yield or quality.
This is not to say that all fields are a candidate for an equal reduction in phosphorus. Land with lower soil test levels of P and/or low pH (lower than 5.8) will require higher rates of P in the blend. This is something to discuss with your agronomist when making fertilizer recommendations. If you are planning to use liquid in-furrow P products, this should also provide an ability to reduce granular P in the fertilizer blend.
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AIM Winter Workshops: Jan 21-22
Our first AIM Winter Workshop series will be held Jan 21-22. The topic will be soil health and cover cropping, and our guest speaker will be Kate Vander Zaag of P&K Vander Zaag Farms of Alliston, Ontario. Kate farms with her husband Peter and family, growing primarily chipstock potatoes. Their farm prioritizes practices aimed at improving soil health, including cover cropping, optimizing crop rotation, use of soil amendments (including on-farm composting) and integrated pest management. Following Kate’s presentation, I will share preliminary results of some AIM trials from 2024, including results from trials on nitrogen credits from legumes, rotational grazing, and more.
Dates and Locations:
Tuesday, Jan 21st at 9:00 am: Emerald Community Centre
Tuesday, Jan 21st at 1:30 pm: Mill River Resort, Bloomfield
Wednesday, Jan 22nd at 9:00 am: Riverhouse Inn, Montague
All growers and AIM industry partners are invited to attend! Hope to see you there