Crop Inputs And Soil Health: How Do They Interact?
Editor’s Note: Trust In Food, a Farm Journal initiative, is working with Soil Health Institute (SHI) to explore the impact of inputs on soil health. The project is made possible through a grant from SHI.
Beneath your feet is a world teeming with life. Mycorrhizae, arthropods, protozoa and earthworms are creatures mostly unseen yet profoundly important to food production. Yet the agricultural community is only beginning to understand the impact that conventional inputs and management practices might have on such creatures, crop performance and, ultimately, soil health.
We asked a panel of leaders including farmers, agronomists and soil scientists to share their perspectives about what we know – and don’t – on the effect of inputs on soil health and on what new insights could shape our understanding of how synthetic fertilizer, biologicals, manure and other inputs, in addition to practices such as conservation tillage, might impact this important natural resource. The perspectives shared are those of the individuals.
The experts who participated in this Q-and-A session were:
• Bill Robertson – Extension agronomist in cotton specializing in crop, soil and environmental science at the University of Arkansas
• Bryan Biegler – Farmer growing 2,500 acres of corn and soybeans in Southwest Minnesota
• Luke Gatiboni – Extension specialist in soil fertility and nutrient management at North Carolina State University
• Ruth Rabinowitz – Farmer growing primarily row crops who owns and manages three farms in Iowa and one in South Dakota
1. How does the use of herbicides, fungicides, insecticides and other pesticides impact or not impact the soil, in your opinion?
Bill: I don’t have any hard data, so I don’t know for sure. But I believe they could have some negative impact on the soil microbiome. But for how long? It could be very short-lived because the soil microbes have tremendous capacity to build up. When there's nothing for them to eat, they kind of just hang in there. But when there's substrate available, their numbers blow up really quick. So it may be something that biologically, yes, they have an impact, but statistically, it could be trivial. I’m not sure we really know yet.
Bryan: I can't say for sure if there is a difference between the two or not. As of now, I am still using synthetic fertilizers. I'd like to be able to reduce the use or eliminate them, but until I find a way to do that – or someone shows me how – I will continue to use them. I have been working on reducing them in small amounts to see how far I can get. In spots where I have shut off the fertilizer for a test strip, I have seen a bit of a hit in the yield.
Luke: In general, the application of chemical substances will likely affect the soil microbiome in some way. However, as characteristics of the soil microbiome will vary with climate, soil type, crops and soil management, it is impossible to predict quantitatively the impact of chemicals on the soil microbiome. In addition, each chemical can affect the organisms differently. For this reason, the impacts of chemicals need to be studied case-by-case. The plants are the best indicators of soil health for farmers. If a given input affects the soil health negatively, it certainly will affect the plant growth and yield.
Ruth: I don't think they’re a positive for the water, for the root systems, for the compaction, for the living activity that’s essentially livestock under your feet. I mean, there's a whole ecosystem under the soil that the naked eye can't see. And these are very, very hard-working soils that have been put in use for decades. So with those acres that are in CRP that are resting and idling, they have a chance to regenerate, which is a great thing. But I’m still dealing with my crop ground and (getting away from synthetic products) is the hardest thing I’ll be doing, because it’s slow going. I have to make a living from these acres.
2. Do you believe synthetic sources of nutrients (e.g. ammonium nitrate, ammonium phosphate) have different effects on soil health than organic sources of nutrients?
Bill: Some of our farmers really watch their fertilizer sources. They do use synthetic sources but will also often use a mixture of poultry litter. They’ll shop around for sources of fertilizer with a lower salt index or rating. The 4Rs are increasingly important to people, and we’re seeing farmers put more emphasis on sources of fertilizer that have the potential for less negative impact on soil microbes.
Bryan: Personally, I don’t think so. Products like phosphorus come from the ground, so I don’t think the effect is different. I could be proven wrong on that, and I’m certainly open to learning more about the impact synthetics might be having.
Luke: Our agricultural crops need an adequate supply of essential nutrients to grow and produce goods. From the plant nutrition standpoint of view, it does not matter if the nutrient source is synthetic or organic, because plants will uptake nutrients in the mineral form. The synthetic fertilizers need to be dissolved, which normally occurs quickly, while the organic fertilizers need to be decomposed to release the nutrients that will be used by plants. Regarding soil health, it is equally important an adequate supply of nutrients and the microbial activity of a given soil. The advantage of using organic fertilizers would be the concomitant application of nutrients and a source of energy (organic carbon) for the microbiome, which could stimulate the soil microbiome. However, if the soil already has a reasonable amount of organic matter, the soil microbiome already has access to organic carbon and, in this situation, probably the advantages of an organic source instead a synthetic fertilizer would be negligible.
Ruth: I think so, though some things like limestone are pretty natural, and it’s useful for managing soil pH. I think the natural manures, seaweeds and root dips can have more natural features that help improve soil activity. I haven't looked at the science, but I don’t imagine the synthetics would have the exact same effects. On too many of our crop farms today, what’s missing is livestock—the buffalo and cattle, with their urine and manure and activity from their hooves. They are a very important part of farming that has evaporated and disappeared.
3. How can farmers know whether adding microbes to their soil will have positive, negative or neutral impacts on the soil microbiome and how long those effects will last?
Bill: I’ve worked with some products for several years in our cotton, and I really didn't feel like I saw much value from them. There are a lot of things that we do in cotton that are Band-Aids—where we're treating symptoms and not necessarily the problem. For example, we get into a situation where we have potash deficiencies that are showing up on the plant. But to look at our soil-test values, potash is really high. But the plants are showing symptomology of potash deficiency because you don't have a rich enough root system to pick it up. So we throw the mandate out to put extra levels of potash out and treat the symptom, when our real problem is a lack of soil structure. When we have poor soil structure, we get poor water infiltration. When we get into the heat of the battle, and the plant really needs moisture and more nutrients, we're handcuffed because we're only farming the top six inches, so the plant can't meet its demand. So we put extra fertilizer out, and then we get into issues with soil microbes. The bottom line is, instead of buying microbes (with the exception of poultry manure) I would rather grow my own bugs.
Luke: Unfortunately, it is very difficult to predict the impacts of adding microbes to the soil. This is because the soil microbiome will vary with climate, soil type crops, and soil management, and it is not possible to predict the interactions between the added organisms and those existent in the soil.
4. What new innovations might be spurred by understanding the relationships between inputs and soil health?
Luke: In the future, I expect to have more products and enhancers based on microorganisms to improve the plant performance and to have better use of non-available forms of nutrients from soils. Understanding the impacts of inputs on the soil system will help us to refine our recommendations to get the best performance of plants with less adverse environmental impacts.
We are just starting to develop tools to measure soil health. As a consequence, we still do not know the best metrics to evaluate soil health and, additionally, the available methods are still lacking of calibration. It means we can obtain a bunch of data from different methods, but the interpretation of this data still needs improvement.
This process is completely normal. It just takes a long time to find adequate methods and to calibrate them. For instance, in the U.S. it took us maybe three decades to develop and calibrate the methods of soil analysis to evaluate the nutrient availability for plants. Nowadays, the soil testing is accurate and it is doing a good job recommending the best rate of fertilizers for American soils. I envision the same process for soil health evaluation: We need a long time to test and choose the best methods, calibrate them, and to develop a reliable way to interpret the results.
Bill: I believe we’ll see a greater use of artificial intelligence to address soil health issues. Artificial intelligence will help give us a better idea of how inputs impact crops, and it will make us more efficient. I think the possibilities with it are almost unlimited.
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