Investigating Best Practices for the Timing and Amount of Organic Soluble Nitrate Fertigation of Hops in the Northeast

Investigating Best Practices for the Timing and Amount of Organic Soluble Nitrate Fertigation of Hops in the Northeast

Summary

During the 2014 growing season, we conducted an experiment to address best practices for organic fertigation in different ages and varieties of hops by comparing: (1) fertigation delivery in either a “set” approach (timing and amount predetermined) or (2) an “adaptive” approach (timing adjusted weekly based on petiole N analysis) and compare these to the current “standard” recommendations of (3) plants side-dressed with granular fertilizer delivered in both a full and (4) a split application.

Due to different planting years for each variety, different age groups were compared for each variety. Specifically, we compared (1) Cascade: 2 and 5-years old, (2) Centennial: 2-3 and 5 years old, (3) Mount Hood: 2-3 years old only (4) Nugget: 6 year old only. Finally, in order to compare whether fertigating is advantageous for 1-year old plants, we delivered a “set” schedule to fertigate 1-year old Cascade plants, and compared with single and split delivery of granular fertilizer.

Objectives/Performance Targets

Hops were strung (2-3 bines/string x two strings/plant) from mid-May to early June using coir twine on 18’ trellising. We tilled around plants in the spring, and used a combination of plastic and straw mulch suppress weeds within rows. Between rows we planted a cover crop of white clover underseeded with oats, which was then mowed after establishment. We amended our soil in the spring with lime, based on previous fall soil tests. We surveyed all plants weekly for insects. When plants are tall enough, we strip the bottom 5’ of leaves by hand to reduce downy mildew infection. We also have a schedule of spraying copper hydroxide mixed with Regalia to control downy mildew.

One granular fertilizer group (“single”) was irrigated and received a full side-dressing of organic granular Oasis 11-0.7-1.0 fertilizer (Lancaster Agriculture Products, Ronks, PA) once in early June, which serves as a control. A second granular group (“split”) split the granular side-dress delivery between early and late June. It is of interest to note that one week after the second granular delivery for the split group, tropical storm Arthur delivered 4.7” of rain in one day (July 5^th), which likely has consequences for granular fertilizer loss in both of these groups.

Beginning in June, we weekly fertigated toward the end of an irrigation event, to retain more fertilizer around the root zone. When the fertilizer injection was complete, the system was flushed for at least 30-minutes to prevent line clogging. Plants in the “set” fertigation group received 18.75 #/acre of Solu-Nitrogen (15-0-0, Ferti Organics, TX), with the goal of providing the recommended 150 #/acre over the eight weeks.  

It is important to note that we intended to use Ferti-Nitro Plus (13.62-0-0), an OMRI-approved soluble soybean-based fertilizer produced by Ferti Organics (Brownsville, TX). However, due to a miscommunication with the supplier, we received a soybean-based product also made by the same company called Solu-Nitrogen (15-0-0), which is not OMRI-approved.

Petiole sampling started on June 24^th, and was done roughly every second week, ending with the fifth sampling event on August 7^th. This consisted of taking 30 petioles at ~5’ high from plants within each age/variety treatment group (n=7). These were mailed to the U. Maine Soil Testing Laboratory (Orono, ME) for nitrate tissue analysis, and results were emailed back to us, usually within 48-72 hours.

When we received the results of the test, we adjusted the next injection of fertilizer to plants in the “adaptive” groups in an attempt to achieve a “normal” range. Since the petiole results showed lower than optimal nitrate levels, the “adaptive” plants received more fertilizer during these weeks.

After our first petiole test results were received, we consulted with an agronomist experienced in routine hops fertigation management using tissue sampling (Agrimanagement Inc., Yakima, WA), and again consulted towards the end of the growing season.

In order to investigate actual N uptake of the hop plant throughout the season, whole hop plant tissue samples (n=3 per group) were taken at cone maturity when harvesting occured (different by variety, ranging from last week of August to third week of September). One whole bine was separately run through the harvester, and cones were collected in a paper bag for total N analysis. The rest of the bine was separated from the coir twine and a subset of it was collected for separate total N analysis. Additionally, 20 petioles at 5-7’ high from this same bine were separately analyzed for petiole N in order to correlate to whole tissue N levels. The U. Maine Soil Testing Laboratory ground the tissue samples and conducted all analyses.

Separately, a group of one-year old Cascade plants were fertigated with the “set” approach (since immature plants do not produce enough bine for repeated petiole analysis), and were compared to single and a split application of granular fertilizer to assess whether fertigation of first-year plantings is worthwhile.            

We held our annual hop harvest field day on Labor Day, September 1^st 2014, and hosted interested members from the general public and the local agricultural community.

In early 2015, some whole tissue analyses remains to be completed at the U Maine Soil Testing Laboratory. When we receive these results, we will compile all data and begin to conduct our statistical analyses. After all the data analysis is complete, we can then write our final report and share it.

Collaborators: