Magic Microbes?

[ Update 7/13/2010

Most of the plants in the beds have matured.  Some did well, other not so well.  I’ve come to believe that the differences in plant hight noted below have a more prosaic cause.  The two beds were built similarly, and are similarly located in the garden, but I suspect that Bed B is slightly more shady, partly because of the tall parsnips going to seed right next to this bed.  Furthermore, I planted the plants slightly closer together in that bed.  Shade and close planting tend to generate leggy plants that may be tall, but are not necessarily more vigorous.

The general health of the brassicas in both beds is only marginal.  The broccoli formed small heads and the kohlrabi is not making much in the way of bulbs.  I’m using drip irrigation, and precise water distribution seems critical for the cabbage family plants.  The lettuce has done splendidly.  Much is starting to bolt and I have selected some plants that I will let go to seed.  The onions are doing well in both beds.  The beds still need much more organic matter to give the soil better texture.  The usual heavy River Road soil problem needed more compost than I had available when I built the beds.  I will be adding more.

All in all, I’m not convinced my application of microbes was effective.  We will try again another time. ]

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About six weeks ago I planted a pair of raised beds with identical seedlings. One bed was treated with various microbes, the other was the control.  The microbes I used were a commercial anaerobic bacterial inoculant EM-1,  and a mycorrhizal fungi inoculant (I believe this was Fungi Perfecti MycoGrow  but am not absolutely sure).  I applied the EM-1 once when the bed was constructed, with the thought it would aid in the decomposition of weeds and compost, and once again about two weeks after planting.  I applied the mycorrhizal inoculant when I set out the starts. It’s time to make the first comparison between the beds because the lettuce is getting crowded and needs to be eaten. So I will be disrupting the experiment at least as far as the lettuce is concerned.  Below are pictures of the two beds.

I made some effort to take comparable photos, but nevertheless they are not taken from exactly the same distance or angle, so direct comparison is difficult.  I’ve labeled them beds A &; B so that you, the reader, can come to your own conclusions.  I’ll identify which is which at the end of the post.

In an effort to be somewhat quantitative, I decided to measure the height of all of the plants in the two beds.  The onions were easy to measure; for the lettuce and Brassica I did the best I could.  The average plant heights and standard deviation for each sample are shown on the chart below.

After staring at the data a little bit, I realized that although several plant varieties showed no statistically significant difference, all the Brassica – the kohlrabi, kale, broccoli and cabbage, were doing better in the inoculated bed.  The differences are big enough that there is almost no chance it’s just a statistical fluke, especially with the kale and the broccoli.

Wow, these magic microbes really work!  But let me temper our enthusiasm with a bit more information.  It turns out that although mycorrhizal fungi are known to colonize the roots of many plants, there are also some plants that they don’t colonize.  Those include beets and all the Brassica! Hence, it seems unlikely that the mycorrhizal fungi are the good guys here because the Brassica were the only plants showing a definite benefit.  If the beneficial critters are the EM-1 anaerobes, then why no performance enhancement for the lettuce and onions?

I discussed this all with our daughter, Liz, who has been studying soil microbiology at Berkeley.  She said that usually bacterial inoculants quickly lose out to native soil bacteria, so they only live for a few generations.  Hence the EM-1 is probably long gone, but perhaps it was helpful in getting the cabbages and kale started.  All of the seedlings were quite small when I set them out, and often the roots didn’t have much soil with them.  Broccoli and cabbages are noted to be sensitive to root damage, so perhaps the EM-1 gave them a boost at this critical time.

As usual, we end up with more questions than answers.

In the photos above, bed A was the control – bed B had the microbes.