Happy Festivus or whatever holiday you celebrate this time of year! One announcement then on to this month’s topic!
We are still taking orders for 2024. Can you believe it? Send your order in as soon as you can. Current members can send in $100 deposit through Zelle (use my email address or phone number), PayPal or a check. New members should order online. Also tell those new friends you made at the company party that they should join too! I’ll credit your account $25 if they mention you were the friend that convinced them to join!
Farm News
This past season we were one of approximately 100 farms that participated in a research project with the University of Minnesota looking at soil characteristics within high tunnels and in their fields. They named it the 100 Farms Project. Not sure where they got the name. Anyway, one of the purposes of the study was to determine why it seems crops in high tunnels (otherwise known as hoop houses) perform really well the first few years but over time production diminishes. We’ve certainly seen this when it comes to tomato production. The first few years we grew tomatoes in our hoop house they did quite well. Then over time their production and quality diminished. Mostly it seemed that each season the plants initially grew well and fast and produced a substantial crop but then “hit a wall” and would stop growing and producing prior to what I would have expected the end of the season to be. I had a lot of theories why but never had the time to run the experiments. So I was glad to find someone who did.
They had four hypotheses: Salts accumulation, Low nutrient levels, pH changes, fundamental soil issues. I had my own hypothesis that I’ll get into after we look at their results.
Their first hypothesis was that an accumulation of salts in the high tunnel stunted the plants growth. Some of you are wondering, why would salts accumulate in a high tunnel but not out in the field? Where are these salts coming from? Do they just like the cozy confines of a covered structure so they walk on over and quietly slip under the door when we aren’t looking? And who doesn’t like a little salt with their veggies? These are all very good questions. Let’s start with the “where are they coming from” question. There are two sources of salts entering the hoop house — the north door and the south door. Just kidding. Salts don’t come through doors. They come from the inputs we add to the soil and in this case it is the nutrients we add (the fertilizers) and the irrigation water.
But don’t we add these to the outdoor fields as well? Shouldn’t these salts be accumulating in our outdoor fields? That is a very valid argument — especially these last few years. The biggest difference between our outdoor space and our indoor space is that the outdoor space is exposed to the outdoors. And what do we have outdoors that we don’t have indoors? Weather! In particular precipitation. In the outdoors some (many, most?) of these salts are washed away or driven deeper into the soil by rain water or snow melt. So they don’t accumulate in the root zone of the plants. Inside the tunnel there is no rain water or snow so no washing away. But won’t the irrigation wash away the salts? Not really since it is adding more salts every time we irrigate. So it is a source of the salts and just adds to the “problem”. I put “problem” in quote because the research found that though salts were accumulating more in the high tunnels than in the fields, they weren’t accumulating to a detrimental effect so their first hypothesis proved wrong.
Their second hypothesis was that the nutrient levels in the high tunnels were being depleted and thus the crops didn’t have the nutrients they needed to grow successfully. The idea was since high tunnels tend to be farmed intensively they tend to deplete the nutrients more so than outdoor field which aren’t as intensive. This did not pan out either. In fact they found the nutrient levels were frequently higher in the high tunnels than in the fields and in one nutrient — phosphorus — it was quite a bit higher (more on this later). So hypothesis two was out.
The third hypothesis was that the pH of high tunnel soil is out of whack. In particular that it is too high. Vegetables like to grow in soil that has a pH between 6 and 7. When they tested soils in high tunnels every single tunnel had a pH above 7. Ours was 7.5. Why does the pH go up in high tunnels? Two reasons. First, high tunnels use irrigation water and most underground irrigation water is alkaline. For example, the pH of our irrigation water is 7.8. The second is that rain water has a low pH. Typical rain water pH is from 5 to 5.5. Since high tunnels use high pH irrigation water and never have low pH rain water they trend toward higher pH over time. Does this affect the production of the plants? I suppose it could though I am not convinced it is a significant effect to produce the observed results — at least at the value we see in our high tunnel. But it is something we need to keep an eye on. I’ll cover more on pH in a future newsletter.
The last hypothesis is that fundamental soil issues affect the growth of plants. These issues included things like aggregate stability and microbial populations. They found no difference in microbial communities inside or outside of high tunnels. However there was a difference in aggregate stability — basically the size of the soil particles — and differences in percolation rates between high tunnels and fields. With high tunnels being quite arid in the winter, soils have a tendency to change texture compared to those that are more consistently wet. Think about how clay responds to being heated and dried. It tends to form hard clumps, something it won’t do if it is consistently damp. Could this be the difference? I don’t know. And I suppose this is one of the flaws — in my opinion — of their research. They didn’t compare the results of all these soil tests with the production output of the tunnels. And perhaps that is just too difficult to measure since each farm could be growing a different crop in their tunnel. I frankly don’t know how this could be measured in this type of study. But their results couldn’t rule out this as a source of the productivity problem.
Anyway, where do we fall in this study? Our results were mostly inline with the other farms. However, one interesting thing to me — and I already knew this but I still find it interesting — is that unlike the vast majority of farms where phosphorus is extremely high, our soils are not. Many of you may be aware that it is illegal in the seven county metro area to sell lawn fertilizer to homeowners that contains phosphorus. That is because the vast majority of soils in the Twin Cities don’t need extra phosphorus so by limiting its use we collectively reduce the phosphorus going into our lakes and streams through runoff. But our farm is unique! Our high tunnel and field measured 9 ppm and 10 ppm phosphorus respectively. The median phosphorus levels for the 100 farms’ high tunnels is 138 ppm. We seem quite low in comparison. More interesting to me is that the Nutrient Management Guide for Commercial Fruit and Vegetable Crops suggests 10 ppm is considered “medium” and “very high” starts at 34. The 100 farm samples median is four times the “very high” level! Yikes for them and Yipee for me!
So of their original four hypotheses, they could rule out the first two but could not rule out — or more importantly prove — the last two. I suppose this calls for an additional study to see if either of these last two — pH or soil structure — actually affect production.
Anyway, that’s enough wording for me and this newsletter. In a future newsletter I’ll discuss what I think is the cause of dropping production of high tunnels, the affect of pH on our farm and how these things affect our plans for 2024. And you all thought I didn’t do anything over the winter…
As always, do not hesitate to contact me with questions, comments, suggestions, share orders or anything else you feel I’d find interesting.
Joke of the Week (Month)
Why do plants hate math? Because it gives them square roots!