Vegetable Farming – March 2017

BY DEREK CHRISTIANSON
March has been full on chilly, while fieldwork has been put on hold for most growers, greenhouses are filling up, and spring projects are getting a bit more attention than typical.  Trading a bit of fieldwork, for off-season training I was able to attend a well designed Produce Safety Alliance workshop last Friday.  Attendance at a similar training will be required for most farms under the new Food Safety Modernization Act (FSMA), and if you missed the trainings this go round, I would recommend keeping an eye out for training sessions next fall and winter.  Despite the chilly conditions are are gearing up for the vegetable season, potting on our early fieldhouse tomatoes, and starting to seed greens, herbs, and brassicas beyond the early alliums.  For the optimists, I reckon a few will be prepping ground on Wednesday and Thursday to get a seeding of peas in ahead of the weekend’s rain.  We’ve got a round of tall vine, Sugar Snap Peas seeded in our greenhouse so we can set out plants in early April; I used to think transplanting peas seemed a crazy notion, but with the difficulty sourcing organic sugar snap peas, it a cost effective way to make the most of small seed supply.  When we seeded last week, I had to make a special trip back to the house to grab rhizobia inoculant, can’t forget the inoculant for peas… If you missed part 1 of my article on seed and soil inoculant from the February Vine, you can find it on the SEMAP website.

Seed & Soil Inoculation Part 2

When it comes to seed inoculants, mycorhizzal use is fast becoming a standard in the industry.  The future use of mycorrhizal inoculants is almost guaranteed after one of the foundational companies researching and promoting their use, Mycorhizzal Applications was purchased by Valent BioSciences in 2015.  I recommend checking out founder Mike Amaranthus’s bio and/or searching online for his lectures as a great online introduction to mycorrhizal fungi.  Depending on your production practices, you may or may not have an active mycorhizzal population in your soils; it’s well understood that tillage and fallow periods will both harm mycorrhizal fungi.  Most vegetable crops, with the exception of the brassicaceae and chenopodiaceae families, are capable of forming mycorhizzal relationships with these special fungi.  What exactly is the relationship?  A simplified version:  through this symbiotic relationship the plants will share resources (sugars, etc) with the fungi, and the fungi will return the favor by sharing minerals with the plants.  The fungal hyphae are able to reach beyond the surface area of root hairs and thereby expand the plants access to minerals in the soil.  Most notably, mycorhizzal fungi are capable of increasing Phosphorous (P) uptake in soils with low soluble Phosphorous.
The importance of this relationship goes beyond nutrient exchange, mycorrhizal have been shown to reduce heavy metal uptake/translocation in certain toxic soils (search for zinc and mycorrhizal fungi) and mycorhizzal fungi have been found to be the source of glomalin, a glycoprotein which helps bond soil aggregates and improve soil quality and carbon retention.  With all these benefits in mind, we have chosen to add new mycorhizzal spores to our crops at Brix Bounty annually; treating the seed is a simple opportunity to allow nature to work with a full tool belt in the soil.  For the greenhouse we typically purchase an all-in-one inoculant; we have been using Lancaster Ag’s Microbial Seed Guard for the past few seasons, other options are widely available through your local fertility dealer or online (in the past we have also followed a diy approach, blending a mycorhizzal product with Tainio’s Biogenesis III to create a broad spectrum inoculant).  Note, Rootshield and Trichoderma products mentioned in February are typically proprietary and would need to be sourced separately if you want to include them in a seed inoculant.

Inoculating Seed – Simple As?

One of the easiest times to inoculate your soils is when you are spreading cover crop seed, with heavier seeding rates than most vegetable seeds, its quite easy to mix a very lightly damp slurry and still ensure good seed “flowability” through a spin spreader or drill.  I also like to recommend inoculating potatoes as an easy way to get started with mycorrhizal fungi.  Coating the seed pieces, we shake a bit of inoculant in a bucket and mix to ensure the tubers are well coated, is a relatively straight forward step and doesn’t require too much extra effort for small growers.  In the greenhouse there are a couple of options; the simplest is to take a very small amount of inoculant (start with the less is more principal) and add it to the seed pack, close the pack back up and shake to spread the inoculant around.  If you add too much inoculant you may end up cursing because it can impact the workability of the seed, especially for small seeded crops where the inoculant can “bury” the seed, it all depends on your seeding method.  Also, certain seeds seem better suited to grasping the inoculant than others, for example pepper seeds are sometimes difficult to achieve a nice coat depending on your inoculant source.  In this case, we have a back-up procedure used for high value crops which does entail using more inoculant per seed (and is therefore more expensive but works well).  We simply use an adjustable salt shaker, with a rotating cap to sprinkle a very light dust of inoculant atop the seeded flat before covering with soil mix.  Alternatively for small scale gardeners using watering cans, you could simply add a bit of inoculant to your initial watering cycle.  At Brix Bounty we use a Hozon injector to occasionally inject a bit of liquid fertility when we are watering the greenhouse, and we have on occasion mixed inoculants into our source bucket which doesn’t require much effort.

Inoculants don’t always need to be sourced from off the farm.  There is increasing interest in the use of indigenous microbes and lactic acid bacteria for soil inoculation, most notably popularized through the Korean Natural Farming (KNF) methods, NOFA/Mass director Julie Rawson provided a really nice overview of KNF in the May 2014 NOFA/Mass Newsletter and I would recommend those interested in learning more to start their search reading Julie’s article.

For folks interested in a deeper dive into the world of mycorrhizal fungi, there are two recently published books which deserve mention.  Mycorrhizal Planet by Michael Phillips was just published by Chelsea Green in February and Timber Press recently released Teaming with Fungi by Jeff Lowenfels.  Of course, Paul Stamet’s excellent Mycelllium Running is a great introduction to all things soil and fungi related.

Is it worth it to use inoculants?  If you haven’t used inoculants in the past maybe split a bed of potatoes and run a side by side comparison on your farm this summer, local conditions will often determine the outcome.  For some growers awash in Phosphorous, mycorrhizal populations might not be a big boost, for others they might be a valuable addition to your growing practices.

The views expressed in this article are contributed by the author Derek Christianson, farmer at Brix Bounty Farm in Dartmouth.  Trade names are used to provide real world examples, but do not constitute an endorsement.

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