Farmers across Iowa are being asked to hold off on applying fall fertilizer until mid‑ or late‑November. The recommendation comes from Iowa State University’s manure‑extension specialist Daniel Andersen and agronomy professor Michael Castellano, who say a super El Niño is creating unusually warm soil temperatures that could jeopardize fertilizer effectiveness if applied too early.
Super El Niño drives the timing shift
“I think the El Niño this year is really the driving factor,” Andersen told reporters. “It will probably delay our peak fertilization window, which creates concerns depending on when we freeze out.” A super El Niño forms when warm Pacific Ocean waters generate unseasonably warm and wet weather worldwide, a pattern currently affecting Iowa’s growing season.
Why waiting matters
Both experts stress that waiting until soil temperatures fall to about 50 °F at a four‑inch depth is crucial for maximizing nitrogen uptake and minimizing nitrate runoff into waterways. “The soil should be 50 °F temperature at four inches depth and falling. In other words, trending downwards to make sure that nitrogen fertilizer will be there in the spring,” they explained.
Applying fertilizer while the soil is still warm can lead to nitrogen loss, reduced yields, and increased environmental impact. Cooler soil not only improves nutrient absorption but also helps protect Iowa’s rivers and streams from excess nitrate.
Practical steps for growers
Farmers are encouraged to send soil samples to Iowa State University labs for analysis. The lab results will guide precise nutrient recommendations tailored to each field’s conditions. Andersen and Castellano agree that the timing this year is especially critical, given the combination of high diesel prices, delayed harvests, and the lingering effects of the El Niño.
“Having to wait an extra week or two to hit prime application season, and then the risk of freezing puts a real burden on getting everything accomplished at this point,” Andersen said. Nevertheless, the experts assert that the short‑term inconvenience is outweighed by the long‑term benefits of a healthier crop and cleaner waterways.
Resources for up‑to‑date information
Growers can monitor daily soil‑temperature updates for their specific area through the Iowa State Mesonet website. The site provides real‑time data that helps farmers make informed decisions about when to apply fertilizer.
While the delay adds a layer of complexity to an already challenging season, the guidance from Iowa State University aims to help Iowa’s agricultural community navigate the unusual weather pattern and protect both yields and the environment.
Original reporting: KCCI Des Moines — read the source article.
