Nathan A. Deppe
Plant Growth Facility Manager
Purdue University – Department of Horticulture and Landscape Architecture
Over the course of fifteen years, I have been fortunate to serve as plant growth facility manager at three prestigious institutions in both Illinois and Indiana. Most recently, my family and I decided to move from my home state of Illinois to West Lafayette, Indiana, where I am now proudly serving faculty at Purdue University – Department of Horticulture and Landscape Architecture.
There are numerous commonalities among all three institutions relating directly to the type of produced crops, design of controlled environment facilities, use of specific substrates, and implementation of integrated pest management protocols. One unique and very important difference, however, is selection of nutrient packages based on site specific water quality.
Purdue processes its domestic water from campus-area wells producing water rich with many minerals except iron. Despite a fairly neutral pH, the alkalinity is generally tested at high levels frequently exceeding 350 ppm. Like many growers, we manage our alkalinity via sulfuric acid injection which inherently reduces pH to a desired range of 5.8 – 6.2. This produces a high quality irrigation water, but it is still rather deplete of plant available iron
This past fall, I spoke with Tom Bosma (Mid-West Territory Manager – ICL Specialty Fertilizer) regarding our water quality, and my desire to provide iron to crops produced within the constraints of our facility. He methodically presented me with several options including use of a new formulation of Petunia Special (20-3-19) containing an updated iron chelate package with “black iron.” Like the original Petunia Special, this fertilizer offers the same amount of iron (0.20%) but has three chelated ingredients that remain available for plant uptake across a wider pH range. Although we work hard to manage the alkalinity of our water, there remains a low concentration that causes a slow increase of media pH resulting in restricted uptake of iron. This led me to the conclusion that trying this product was a worthwhile endeavor.
Our first shipment of fertilizer was received in late fall, and I decided to waste no time on providing this new product to all of our growing zones. After mixing into our concentrate tank, I programmed our controller to inject 150 ppm N into our acidified water source. Once our fertilizer lines were charged, my staff and I started using it immediately. Understandably, the frequency of use depended on the crop and its current growth stage. Young plants received fertilizer once per week or on alternate days, and larger high-demanding crops were continuously fertigated with the solution.
Within a couple weeks one could easily tell that a new fertilizer formulation was being used on site and that it was succeeding at what it was sent to do. A commonly used inbred maize line, B73, frequently experiences iron chlorosis when produced in controlled environments. After using this product, we found no maize plants experiencing this disorder during winter and early spring. Plants remained remarkably green, vigorous, and highly productive.
The Purdue Student Farm uses resources at the HLA Plant Growth Facility to hydroponically produce Thai and Italian basil varieties for sale to university dining halls and caterers. Their nutrient film technique reservoir tanks are filled with fertilizer solution from our in-house supply system. Historically, they have experienced bouts of sporadic iron chlorosis which was attributed to temporary failures of our central acid injection system. The new fertilizer formulation has greatly helped reduce yellowing of plant material thereby making them far more marketable.
Lastly, plants produced for the annual Horticulture Club spring sale event where done so using the new fertilizer formulation too. Lobularia, pelargonium, coleus, and impatiens, were just a few big sellers, but the namesake of this fertilizer blend, petunia, was the takeaway attraction. They were compact and full of radiant blooms. I wasn’t surprised at all after seeing this fertilizer’s track record earlier in the season. So marks another victory.