Because soil throughout the West is highly alkaline, spud growers who attended the 44th Annual Idaho Potato Conference on Jan. 18 were urged to carefully monitor and regulate their phosphate fertilizer applications to ensure bountiful crops.
Hundreds of potato producers from throughout the state and Northwest converge at Idaho State University in Pocatello each year to attend the conference and the simultaneous Idaho Ag Expo, where the latest in large harvesting equipment is displayed at Holt Arena.
“Try to get the concentration of phosphorus early when the root demand is high,” panelist J.P. Kruckeberg of Stuckenholtz Laboratory in American Falls admonished dozens of growers who packed an ISU meeting room. He said he has seen good success over the years efficiently applying phosphate concentrates in water.
Kelly Hurst, a Blackfoot agricultural consultant, cautioned against plugging irrigation wheel line nozzles with center pivots when broadcasting liquid fertilizer on fields. “Water-run phosphorus should be looked at as a supplement, not the main course.”
Depending on the soil, which usually has a high pH level, there can be “a huge difference” in the amount of phosphorus needed for efficiency, Hurst said, noting that land intensely farmed for many years with phosphorus applications generally tests low for acidity. He recommended using good starter fertilizers for potatoes. “We’re dealing with a short season. The crop needs a good boost.” Starter fertilizers are needed at the start of a growing season because research shows phosphorus already in the soil is “in a lock box, not a bank account where you have easy access.”
Kruckeberg said it is important to have a reserve amount of phosphorus in the soil for good root growth. Phosphate does not move much in soil, unlike nitrogen and sulfur.
Travis Morgan with Bingham Cooperative of Blackfoot warned about improperly mixing liquid fertilizer in spray tanks. “It’s not fun to pump a bunch of Jello out of the tank,” he said.
Amber Moore, a University of Idaho extension soils specialist from Twin Falls, noted plants are designed to take up nutrients through their roots, not leaves. Potatoes have a “tremendous network” of roots near the surface, Hurst added.
Panelists agreed matching zinc with phosphorus is important because most soils tend to be low in zinc. Feed lots and corrals have high phosphorus levels.
Hurst advised growers to be cautious with new phosphate fertilizers that can be so cost prohibitive that farmers would be tempted to neglect boosting low phosphorus levels in soil. “There are whole different variations. There’s good, bad, and ugly to anything.”
Asked about comparative yields of fertilizer phosphate versus manure phosphate, Hurst said he would avoid using manure in potato fields, noting manure and compost behave differently. It is difficult to spread manure easily, but extremely good crops of potatoes can be raised with compost, panelists said.