Soil Testing Shows Your Balance
By Carol Miller, Editor, American Vegetable Grower
Fertilization programs have historically been simplistic, focusing primarily on N-P-K, with calcium for acidic soils. It’s all applied before or at the beginning of the season with most of them running out just when the crop starts to really need them. Then later-on during the season, typically nitrogen is applied to boost crop growth and yields.
With research on soil testing having begun in the early 1800s, the concept is hardly new. Yet many still consider the costs and trouble to be unnecessary.
Now, with the gyrating costs of fertilizers and consciousness of pollution of waterways and other environmental factors, you may be compelled to achieve maximum efficiency from fertilizer and to minimize waste, especially into the environment. Soil tests are the obvious way to start growing smart.
We spoke with one of the top plant sap, soil, and irrigation water quality consulting experts in the country, Noel Garcia, Certified Crop Adviser (CCA), Senior Consultant and COO of TPS Lab in Edinburg, TX, to better understand when to test and what tests are most appropriate.
Why Test? Garcia describes a soil test as an audit of your nutrients savings account.
“You’d be surprised how many nutrient ‘hidden assets’ your soil can have, often in abundance, but that are unavailable to the plant because they are ‘locked-up’ as insoluble compounds. At least some can be fairly quickly released with proper treatment and biology,“ he says.
You may have more nitrogen in your soil than you think, for one. That allows you to reduce the amount applied.
“Also, you may find you have needed nutrients that traditional N-P-K applications cannot unlock or make them available to your crops. In fact, those applications may actually only add to the unavailable reserves,” Garcia says.
Tests can also reveal your baseline soil health. A healthy soil can biologically unlock at least some of those nutrients for your crops.
“The overall microbial biomass of the soil helps break up those nutrients and change otherwise unavailable compounds into more bioavailable forms.”
Some of lesser-known and often ignored nutrients important to soil health are zinc, manganese, copper, cobalt, and boron, among others. Zinc is a good example of how a micronutrient can change your fertilizer approach.
“Zinc is essential to enhance the overall genetic potential,” Garcia says.
He says just a few parts per million of zinc can take 200 bushels of corn to 250 or even 300. But it requires the right timing and the right amounts.
“The existence of certain minerals improves yields, improves quality. This applies to all plants, all crops,” he says.
Some elements can inhibit uptake of other elements, while others improve uptake. Too much phosphorous early in the season, for example, can lead to a zinc deficiency.
“It’s all about balanced nutrition. When you start increasing one element, you can start inducing deficiencies of others,” he says.
Tests to Consider Using There are a lot of labs across the country that growers can choose from, and each one will have its own protocols and preferred tests.
“Labs are typically regional in nature — some even performing testing only within a few counties around them. This is because they employ methods that do not emulate the way plant roots take up nutrients. Accordingly, they have to estimate (guess at) interpretations and recommendations based upon their experience of the area over years,” Garcia adds.
TPS Lab has a few tests it prefers.
Organic Matter Levels. This measures what is in reserve for future growth. Garcia uses a method he considers to be the most accurate for active organic matter but also offers the LOI (Loss-On-Ignition) method for total (both active/composted and uncomposted) organic matter.
Solvita. This test for respiration may be used to estimate potential mineralizable nitrogen. When carbon is released from the soil as CO2 due to microbial metabolism, the nitrogen associated with it may become available. If you have more CO2, you’ve got a strong microbial biomass, which translates to having more bio-available nutrients.
Going back to Garcia’s banking analogy, this and other tests give you an inventory of your soil’s nutritional reserves.
“Do I have enough in my savings account that I can possibly move over to my checking account? Or do I have to supplement with additional fertility, so I can have both some reserve for future growth and immediately available now?” Garcia says.
Soil health is a big part of the answers to these questions, he adds.
“Do we provide a habitat with good internal drainage and more aerobic conditions for the microbes to thrive? Second thing is, we’ve got to make sure that we’ve got the soil’s chemical and biological aspects to where we can balance it properly in season,” he says.
There are now a lot of organically derived amino acids, hormones, and other products, which can be real game changers for crop and microbial performance. It can mean the difference between success and failure, or a mediocre crop versus an outstanding one, Garcia adds.
Sap Analysis. The purpose of a sap analysis is to give your plants only what they need when they need it, Garcia says.
“Sap analyses done at critical stages of development of the crop during the growing season are crucial to the yields and quality (nutritional value, flavor, durability in shipping, and shelf life), as nutritional demands can vary dramatically during crop growth. We must be able to accommodate those demands on a very timely basis,” Garcia states.
A lot can happen to your fertilizer after it hits the ground, however. And there is the question of what Garcia labels efficiency of uptake by the plant, plus many other factors. Without a sap analysis test, you really don’t know and may not be able to predict how much of what nutrients actually get into the plant, he says.
“Sap analysis also allows you to forecast up to 21 days in advance, to see when a deficiency may kick in,” Garcia says. “By the time problems become visible in the field, the crop has already suffered irreversible loss for the season.”
That early warning can make all the difference, he says.
“When we encounter a crop with disease or insect problems, we immediately want to know the plants’ nutritional status. We know from long experience that these problems are very most often caused by plant stress due to nutritional imbalances or deficiencies in primarily the micronutrients and trace elements”.
Timing Matters For most growers, you’ll need to run tests at no less than two critical points.
“When the plant comes up, less than six inches or so, we try to do a test there. The other important part is transitioning from vegetative to the reproductive stage,” he says.
Garcia says his more progressive growers test more often.
“I work with a lot of watermelon growers. We analyze [the vines] on a weekly basis. Of course, they use drip irrigation, so we can ‘spoon-feed’ the plants on a weekly basis and mitigate, if not outright eliminate, issues all season,“ Garcia says.
The timing of applications is much more beneficial and efficient than applying a large amount upfront. Precise timing of the right inputs can save you a great deal. In the first 30 to 45 days of growth, the plant requires less than 20% of its nutrition for the entire season.
“So why do you want to put all that up front? The soil is a very expensive, inefficient, and leaky storehouse, and the plants can’t utilize it”, Garcia says.
Applying too much at the beginning of the season can also lead to disease issues, requiring more (expensive) fungicide applications than you would otherwise need.
“Once you get into the stage of higher demand, then you start feeding at that transitional stage. The plant can utilize it when it requires it,” he says.
Irrigation Water Quality: Often Overlooked Poor water quality can have a tremendously bad impact on soils and plants, Garcia says.
In calcareous soils, which many growers have, hard water can change native soil chemistry and structure, plugging-up soil pores and making it almost impregnable to water. And salty water can kill crops outright, he says.
Garcia mentioned that he had a nursery client who had container plants and trees dying left and right.
“He pulled a tree out of its container and the media and roots had turned to chalky stone and the roses looked like they had been hit by fire. An inexpensive water treatment started it all turning around inside of a week,” Garcia says.
Additionally, hard water will leave mineral residues in spray tips and on leaves, which plug-up the stomata, leaving the plant unable to breathe or absorb foliar-applied nutrients.
Minerals in water can also change or neutralize the chemistries of fertilizers and foliar sprays, making them ineffective or precipitating-out in sprayers.
“The good news is inexpensive treatments can be used to very effectively mitigate and even reverse many water quality problems,” Garcia says.
Years ago, Garcia received a call from a client who said that he had asked the local university consultant if anything in his irrigation water could be causing his problems. The consultant said he didn’t know. It was after that call the lab coined the phrase, “What’s in Your Water Becomes Part of Your Soil.”
Interested in getting started? Garcia recommends finding a lab that emphasizes education so that you will have a clearer understanding of your reports. TPS Lab color-codes its reports, each color indicating the interpretation of lab data and provides clear specific recommendations. Otherwise, it can be difficult interpreting the analysis reports.
The more you are able to make your own decisions, the more control you will have of your crops’ performance — and your bottom line.
