Starve to Death? – Or Prevent Plant Nutrient Deficiencies

A nice stroll in the garden – but what did I find – unhealthy plants! My tomatoes were spindly, and the leaves were a bit on the yellow side. My lettuce seemed to be a beacon for all kinds of pests. I thought I’d prepared my garden bed well; I’d tilled in lots of compost and leaves - what was the problem?  That question led me on a quest to find out how I could have healthy soil (according to the State Extension Service soil test) but have plants with nutrient deficiencies. This is some of what I found out.

The Difference Between Macro and Micro Nutrients

The soil test only tested for pH and macronutrients – and not even all of them.

Plants need at least 17 essential nutrients. The macronutrients are carbon, hydrogen, oxygen, nitrogen, potassium, phosphorus, sulfur, calcium, and magnesium.  That already was more than my usual NPK. I hadn’t even considered the micronutrients such as zinc, iron, copper, boron, manganese, chlorine, molybdenum, and nickel.  Heck, I hadn’t even thought of most of those elements since high school chemistry class!

The macronutrients are needed in – you guessed it – large amounts.  That’s why they’re tested for. The micronutrients may only be needed in small amounts but are crucial to avoid soil and plant nutrient deficiencies.

The whole is bigger than the parts, especially in plant and soil health. Too much of one nutrient will block other nutrients from being taken up by the plant. Too little, and the plant won’t grow well or produce malformed fruits.

The plant’s root mass seeks out nutrients. If they’re not in plant soluble form, they might as well not be in the soil as far as the plant is concerned. For those nutrients to become plant soluble, they need the action of microbes. 

The Power of the Microbial Community

Nutrients in the soil are constantly changing at the molecular level because of the activity of microbes. Soil is a living, breathing, moving city of inhabitants who can be seen only with a microscope.  A teaspoon of soil has more inhabitants than people on earth. They come in many shapes and sizes and have many different jobs.

Bacteria consume the simple sugars in the organic matter, while Fungi consume the more complex ones. Protist, nematodes, and other larger (but still microscopic) inhabitants are predators to the bacteria and fungi. Like all organisms, these predators release the nutrients they don’t need. Lucky for the plant that micro-poop contains soil nutrients in plant soluble forms.  I imagine the plant roots sucking up that feast, spreading the goodness throughout the plant, and the end result is great-tasting tomatoes.

Along the way, those microorganisms make sure the plant is healthy because they have two sources of food – the nutrients in the soil, and exudates the plant exudes from its roots. Without both sources, the microorganisms can’t be 100% efficient because they don’t have all the nutrition they need.

Not only do the microorganisms make sure the plant has the nutrients it needs, but they also guard the plant against pathogenic microorganisms. The more beneficial microorganisms around your plant roots the fewer spaces for pathogens to slip in. Those plants are a major food source for your beneficial microorganisms, they don’t want the food sources to die! 

The plant nutrient deficiencies we observe are tied to the health of the soil microbes and soil in general.  It’s hard to see soil nutrient deficiencies, easy to see plant nutritional deficiencies. So, we start with a yellowing leaf or spindly plant and work backwards. Symptoms of plant nutrient deficiencies are our cues to look at the soil and see what we can do to balance the nutritional composition, and keep our microbes happy.

Soil Tests to Uncover Nutritional Deficiencies

My spindly tomatoes may be showing symptoms of a nitrogen deficiency. But does that mean I should spread some fertilizer (NPK ratio 3-1-1) high in nitrogen?  If I’ve been tilling my garden, there may be more important problems to solve than just a lack of nitrogen. In fact, if I don’t solve the other problems, it won’t matter if I keep adding nitrogen, I’ll still keep having plant nutrient deficiencies.

Soil tests are critical for profitable crops, even if they only measure NPK and pH.  They give you a starting point, and they can give you an idea what it’s going to take to reach your goal.  How often do you start out on a trip without GPS, without a map, without a destination in mind? Not getting a soil test is similar to driving nowhere!!!

Plant Analysis for Nutrient Levels

Plant analyses give an indication of which nutrients in the soil are making it into your crops. Just because the nutrients are in your soil doesn’t mean the conditions are right for those potentially available soil nutrients to actually be taken up by your plants. If there are nutrient deficiencies in your crop, but the soil test comes back with adequate nutrients, then you know it’s not a nutrient issue. Before you, or I, start adding nitrogen fertilizer to tomato plants showing symptoms of nutrient deficiency, we need to look at a number of other variables.

Very often, there’s a difference between the nutrient levels in the soil and the plant.  There are many reasons for that, root damage, insect infestations, too much moisture or too little, soil pH, and the health of the microbial community are a few. Plant analysis measures a particular part of the plant at a particular stage in the growth cycle.  Plant analysis tests are standardized for each crop.

Nutrients in the soil

The two tests used together let you know if any deficiencies in your soil are leading to plant nutritional deficiencies.  The soil deficiency may very well be a microbial and not a nutrient issue so adding fertilizer not only doesn’t solve the issue, it adds to nutrient runoff to lakes and streams.

Steps to Help Nature So No Plants or Organisms Starve

There are numerous ways we keep nature from performing at optimum level. Excessive fertilization, tilling, and continuous monocropping of a specific crop all lead to nutrient-deficient soil. They also lead to less diversity in soil microorganisms which creates inroads for pathogens.

Tilling soil destroys the microbial community. Leaving soil bare between crops leaves the microbes you do have with nothing to eat, they starve. When the field is planted again the more robust microorganisms, which have a tendency to be pathogenic, populate fields and crops first.

Should the first-line solution be fungicides and bactericides? What if a humic acid soil amendment that promotes then…

…Compost spread on the field and cover crops planted?

The compost has beneficial microorganisms, the cover crop roots feed exudates to the microorganisms, the micro-poop feeds the cover crops. And…

…If you don’t till but plant your cash crops into the cover crops after they’ve been crimped (not chemically killed)…

…You’ll have a long-term plan for soil nutrients and strong microbial communities. If you feed the soil, nature will take care of the rest.

The Solution to Plant Nutrient Deficiencies Sounds Simple

But it’s a long game. It starts with healthy soil.  Creating soil high rich in with the beneficial microorganisms takes planning. Nature gives us lots of soil health solutions but also lots of variables, including:

  • water holding capacity
  • compaction
  • drought
  • microbial communities
  • nutrients naturally available from bedrock
  • amount of organic matter

As a grower, your job is to optimize all the variables. In order to do that, you have to know what they are.  That’s why soil tests and plant analyses are so important.  At the beginning of your season’s journey, you test your soil. When you’re about halfway to your destination, you do a plant analysis to see if you’re on the right road. It’s impossible to turn back midway, but you may have time to take a detour of an addition of a humic acid soil amendment to create balance in your soil. It’ll get you ready to zoom down the freeway next year.

Now, What About My Tomato Plants

After reading about soil health and plant health I took three actions

  1. Reread my soil test

It said I had sufficient N for vegetable crops. So, what was wrong?

  1. Dug around my garden looking for worms. They’re an indication I have living soil, without having to buy a microscope. I found two. Not enough. That told me my soil was barely alive.
  2. Added humic acid to kick start the plant biology in my entire garden

That would increase the living part of my soil. I increased the humic acid and fulvic acid.  I also added a deep layer of mulch in the form of half-decomposed leaves from last fall. There should be plenty of microbial activity in those decaying leaves, I saw plenty of fishing worms as I pitchforked it into the wheelbarrow. Then I watered well.

  1. Committed to not tilling my garden

I’ve been killing off the microbial life in my soil by tilling. The effects of tillage on soil health are well documented. I wanted nutrient-dense food, that’s why I grow it myself. I suspect the nutrient deficiency I observed in my tomatoes doesn’t have anything to do with the N in the soil but with the lack of microbial activity.

Took a stroll in my garden a week after I added soil amendments.  My lettuce has bolted, but the leaves no longer look like they’re being devoured by insects.  My tomatoes…

… No tomato hornworms, beautiful green leaves, blossoms and fruit set. It was a happy stroll.

I’m not saying you can have instantaneous results – especially on a large commercial scale. But taking care of the soil made a big difference in the health of my plants. I haven’t had a plant analysis done, but would if this were on a commercial scale for three reasons:

  1. Healthy plants are more productive, leading to higher profits
  2. If you can verify your crops have a higher nutritional profile chances are they’ll be worth more on the market.
  3. In the long-term, it’s good to know the correlation between the nutritional profile of crops and the nutrient profile of soil.

Build your soil health with organic amendments, and your plants will thrive!

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