Monday, August 4, 2014

Branching out with Brassicas - Summer trial in NFT production in Ohio

Branching out with Brassicas
Summer trial in NFT production in Ohio
Natalie Bumgarner, PHD


In the greenhouses that I visit and crops I discuss with growers, it is clear that lettuce still fills a majority of plant spaces in the NFT system. However, we field an increasing number of questions about the many other leafy crop possibilities. Many of the other leafy options are in the Brassica family - cabbage cousins, essentially. These include kale, mustard, mizuna, and pac choi most commonly.

These options present growers a chance to diversify to attract new customers as well as provide more product to existing customers. One of the challenges with any new crop is understanding its production capacity to assist in pricing and tailoring production to anticipated demand. Also, there is the potential for higher light and temperature to negatively impact quality in the summer as is the case for some lettuce and other leafy crops. This trial was designed to evaluate a selection of Brassica crops as well as amaranth (not a Brassica, by the way) under summer conditions. Rather than extensively trialing multiple cultivars of the same crop, the goal was to evaluate production capacity and crop quality of a selection of alternative leafy crop
options to lay a broad foundation for future work.

Methods and Management
Seeding was done by hand into pre-moistened cubes. Three media were compared in this trial- rockwool (25 x 40 mm), Oasis (162 count Horticube XL), and a peat media (162 count, Grow-Tech). Seeds were germinated in clear water in seeding trays, and were transferred to the nursery and nutrient solution 3 to 5 days after seeding. Seedlings were produced in flowing nutrient solution in the nursery for an additional week to two weeks before transplanting (no supplemental lighting was provided during the seedling phase). After transplanting, plants were grown out in the channel until harvest. The nutrient solution was continually cycled through the Fertroller where automatic pH and EC adjustments met programmed solution set points. The pH was maintained at 5.8 by the addition of dilute sulfuric acid. EC was maintained at 1.7 to 1.8 by the addition of concentrated fertilizer solution and source water.

* This trial measured single harvest yields to produce the most accurate and comparable yield totals. However, some growers may harvest single leaves or leaflets from kale or amaranth plants. This could increase the total yield per plant but require additional time in the channel and quite honestly make comparisons much more challenging.

Timing and Conditions

Biomass Yield
* Amaranth was seeded with multiple seeds per cube as is typical in production, but this increased the yield variability.

Some thoughts on the trial

After considering these trials, there are a few things that I would like to bring up for discussion.

  • First, I should report that there were very few quality issues with any of these crops in these trials. They grew through the OH spring and summer conditions quite well with no losses or issues to speak of.
  • Second, and most clear in the data, we can see that the yield potential of these crops is wide ranging. That is really an understatement. In fact, we had to use two different scales to weigh these trials. Besides our scale challenge, there are two key grower impacts. One is the fact that timing of transplanting and harvest really should be varied. The kale maybe could have been grown a bit longer and the WinWin Choi should have been harvested earlier for highest quality. The other important point is that it will be important for any grower going into sales with such crops to do a few trials before setting prices. We can often count on bibb lettuce to finish out at predictable weights at predictable times, so prices can be set and costs calculated simply. When selling and pricing kale, pac choi and the like, be aware that yields and therefore input costs per weight of produce vary. Don’t undersell yourself early in the process of growing a new crop.
  • Thirdly, the impact of our different growing media was not clear in these trials. This is certainly my least favorite point as unclear results frustrate every researcher. In looking at the yield trends between the two runs, the differences (or lack thereof) between rockwool, oasis, and the Grow-Tech cubes were not consistent. In run 1, the peat cubes tended to perform better while that was not seen in run 2. Environmental conditions were reasonably consistent in these two trials, so that is unlikely to be the primary cause for these inconsistencies. I am hesitant to draw too strong a conclusion about this on early trials, but I will say that it may be differences in germination speed, moisture content (and therefore fertility), temperature and the like early in crop growth that led to these variations. We generally deal with pelleted lettuce seed that produces very consistent germination and early growth. Because these Brassica crops are not bred for controlled environment production, their response to small differences in conditions may not be as well understood at this point in time. More focus on the seedling aspect may well be needed.
Notice the difference in germination rate and seedling size between the five crops in this trial. Tiny amaranth seedlings are in the back of the tray.
Plant Images from Run 1

Toscano Kale- At harvest (44 days after seeding)

Red Giant Mustard- 44 days after seeding

Red Choi- 44 days after seeding

WinWin Choi- 44 days after seeding

Red Leaf Amaranth- 44 days after seeding