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  • Writer's pictureRachel Cobb

Watching Soil Improve Before Our Eyes

Our soil management doesn't fall exactly into one philosophy- we're a little bit regenerative, a little bit no till, a little bit organic. I feel very strongly that the way you manage your farm fertility needs to be tailored not only to the needs of your land, but also the resources that are local and available to you. It doesn't make sense for me to ship in truckloads of compost, minerals, or soil amendments from other places; but I can save every scrap of organic material from our farm for my own compost pile, and use the abundant leaves we have in our area to provide minerals for the soil. The only amendment I consistently buy and ship in is kelp meal because I love the way it packs a double punch of trace nutrients and hormones that help plant growth. If you enjoyed our onions this year, I SWEAR I could taste the kelp meal in them! The other great thing about kelp is that it is an organic material that slowly breaks down and feeds the soil, rather than a powdered mineral or processed fertilizer that would wash right out of my VERY sandy soil.

Speaking of sandy soil, the first year we bought the farm I had soil tests done on all the fields, and the results were almost nothing but sand. Our poorest field tested at just 1% organic material, and the best at 2.2%. For context, it's recommended that your soil have 5% organic material AT MINIMUM to grow vegetables. Organic material is what makes up lovely black dirt- all the good stuff from rotten leaves, compost, manure, wood chips- pretty much anything that can decay into the soil. Organic material is what allows soil to have the correct electrical charge to hold onto nutrients- without it, almost anything you add is washed away by rain before it can feed your plants.

So for the last five years we've added every bit of organic material to the fields we can get our hands on. Horse manure, fallen leaves, wood chips, straw, lake weeds, and compost. Until we got our tractor a couple years ago I was hauling these things around with a wheelbarrow and flipping compost piles by hand with a pitchfork. While I am very grateful not to have to do that level of backbreaking work anymore, it was all worth it. Last November we had another round of soil tests done, and saw improvements across the board. The worst field jumped up to 1.7% organic material, and the best field is now

at 3%. I was encouraged to see that the levels of trace nutrients like magnesium and boron have risen as well. The act of harvesting the vegetables I bring to market removes fertility from the soil, and it is both incredibly difficult and important to actively replenish and improve the soil at the same time.

So what did our soil health look like this year? This was the year I finally felt like I could create ecosystems in each field to feed the soil and the vegetables at the same time. We've been experimenting with a cover crop system for tomatoes the last few years and I am so happy with how it turned out this year.

The fall before the growing season, I plant the prospective tomato field with a cover crop mix of winter rye and hairy vetch. Rye is incredibly tough and stays green all winter, and grows a thick, strong root system. Hairy vetch can actually move nitrogen from the air into the soil through its roots, and it also can activate genes in tomato plants to make the fruit taste better.

In late spring when the rye is mature and has seed heads, we flatten the whole field and cover it with a tarp to kill it completely. This leaves me with a clean field with straw mulch already in place, ready to plant.

After planting the tomatoes into trenches with drip tape and a trellis for support, I have a lush field of tomato plants that need no weeding, mulch or maintenance. With the systems we used of cover crops and mulches, I did less weeding this season than ever before. And with the soil covered for the whole season, I saw practically no fungal or leaf diseases on the tomato plants at all. I was terribly proud to have such a large, delicious tomato harvest with no spraying whatsoever.

While I have been refining this tomato plant system for the last 5 years, we tried a new cover crop system in the garlic field this year and I am very pleased with the preliminary results. If you aren't familiar, garlic stays in a field for a long time and requires a lot of nutrients. I generally plant our garlic bulbs in October and they aren't ready to harvest until the following July. I always cover the garlic with a thick layer of leaf mulch in the fall to protect against frost or early fall sprouting. I have found that if I just leave this mulch on the garlic, it has no problem sprouting up through it in the spring and there are no weeds to deal with in the rows.

In this picture you can see the garlic field in June- tall healthy plants with no weed competition in the rows. (As a bonus, if you peek in the foreground, you can see the curly green scapes sprouting up out of the plants. We remove these flower buds to encourage the garlic to produce larger underground bulbs- plus they're delicious!)

While I was happy with how I grow my garlic, I have struggled over the years to find solutions to pathways that don't turn into a weedy mess. I have found that landscape fabric, while effective, tends to smother the soil underneath and certainly doesn't help with overall fertility. I was looking for something low maintenance as well, because once heavy vegetable harvests start in August there is no way I can keep up with mowing the fields and weeds can quickly get out of hand. I settled on white clover because it is perennial here in Minnesota and incredibly tough- foot traffic and mowing doesn't phase it one bit. The other really cool thing about clover is that it can form a symbiotic relationship with rhizobia bacteria. These bacteria can take nitrogen from the atmosphere and convert it into a form that is usable by the plant. Here is a picture I took of some clover I accidentally uprooted in the field. The rhizobia bacteria live inside the round pink nodules on the roots.

To establish the clover pathways, I first inoculated the seed with the correct rhizobia strain. Different strains are compatible with different plants and while the bacteria are naturally found in the soil, for the most nitrogen-fixing benefits it helps to coat the seeds with the correct bacteria they will need while they grow. We raked the seed into the soil and watered it as needed. Clover really thrives in cool seasons and it was a challenge to establish it in this droughty summer! To allow the plants to get established without too much weed competition I mowed periodically, with the mower set at a height where it wouldn't really cut the clover but would cut any weeds that were trying to poke up seed heads.

Here is what the field looked like at the end of July after we dug up all the garlic. You can see that the leaf mulch is still doing its job of suppressing weeds, but the pathways are still a bit of a mix and I was mowing to keep the grasses from taking over.

This was the first season where I was "organized" enough to actually put in a crop after garlic. It can be challenging to plant a field at the end of July and have enough time to harvest before heavy fall frosts. Garlic also takes a lot of nutrition from the soil and can make it difficult for any plants to follow. I settled on broccoli and small cabbages as well as radishes, mostly because we have such a demand for those vegetables, and they mature quickly enough to harvest in October.

Here you can see what the rows looked like in September. I decided to plant each "big" vegetable (broccoli or cabbage) with a row of radishes or carrots underneath. This season I consistently found that vegetables grew better and tastier when they were planted with "friends." I suspect one reason for this is that different species contribute different things to the soil microbial life and as with everything else on the farm, more diversity is always a good thing.

As you can see in the pictures, by September the clover had spread enough that it had effectively smothered all other weeds and formed a lush green mat. I couldn't stop taking pictures of this field because the riot of lush green growth was so visually satisfying.

The plan is to allow the clover to grow for another season or two in the pathways. It will continue to spread and suppress weeds, and next summer it should flower and provide valuable nectar to our honeybees. Eventually, I will smother the clover with tarps just like the rye field to kill it. Once the clover is dead the nitrogen at its roots will release and become available to the crops, and the thick upper foliage should make a beautiful mulch. I will switch over to planting crops in the clover pathways, plant clover or another cover crop in the current mulched beds, and start the process all over again.

This is perhaps my favorite thing about farming. I love finding ways to create balanced and diverse ecosystems, and work with the natural flow of life rather than against it. If I was tilling this field every season I would be dealing with never ending new flushes of weeds, as each pass of the tiller brings up new weed seeds to germinate and grow. I can create an ecosystem that benefits both me and all life on the farm- from the skinks that skitter through the clover cover to the honeybees that collect nectar from the flowers.

Stay tuned to see what soil adventures we embark on next. I love this winter season of rest and research! I am currently working on an exciting intercropping system to hopefully bring more health and better flavor to our melons next season.

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