Soil moisture levels and in-row applied phosphorus rate influence field pea mortality

As part of an Alberta Pulse Growers Zone 5 funded project, Lakeland College’s applied research department explores field pea seed safety and yield potential by applying increasing rates of phosphorus (P). Lakeland's Student-Managed Farm — Powered by New Holland (SMF) crop research unit kicked off the project by looking at field pea P fertility in April 2019. They designed the project with interest in both the seed-safe amount of P to place with the pea seed and the total rate that would be economically profitable in the fertilizer side-band. They discovered that field peas are sensitive to seed-placed fertilizer, causing mortality. Yet, P is not mobile in the soil for seedling roots to access early in the growing season when it is most needed, so seed-placement of a maximum safe rate of P with peas is of great interest. In the second trial, students tested P rates in the side-band from zero to 60 lb/ ac actual P to see how the total applied P amount affects yields, but more importantly, where the best economic return for farmers would be.

“We’ve looked at a couple of different things, not just yield, such as the mortality. In 2019, we found higher mortality as the [seed-placed] P rates went higher. It went up every 15 pounds, between zero and 60. When we got to 45 and 60, we found that mortality was significantly higher, which resulted in fewer plants per square metre than we did from zero to 30,” says JP Pettyjohn, Lakeland’s crop research scientist. He continued to explain that in 2020 they saw little mortality; however, the expectation from 2019 was higher pea mortality with increased seed-placed P levels. The difference between the two years is soil moisture levels. “In 2019, we started with reasonably good soil moisture, but then we saw no rain until early June. We went, after seeding, for almost 30 days with no rain. In 2020, we got significant moisture. The seed-placed P itself is not toxic to the plants, but it draws moisture. Water tends to move from areas of low salt concentration to areas with high concentration. When soil water around the seed is high in salts, water cannot enter the seed to start germination. When soil moisture is high and early rainfall occurs, the salt is diluted more so seeds can absorb water.” Pettyjohn says they would conclude that in the years with adequate soil moisture and sufficient rainfall, you can apply We’ve looked at a more seed-placed fertilizer couple of different without an effect. However, things, not just in the years with low soil moisture and insufficient yield, such as the rain, it would have dire mortality. consequences.” Thus, the need to determine a safe seed-applied rate is important to ensure a healthy and vigorous plant stand every year no matter moisture conditions. He added that Alberta Pulse Growers Zone 5 is interested in signing off on the third year of trials to test lime soil amendments to combat Aphanomyces at a field scale level. Results from the project will likely become available in 2022.