March 8, 2023 at 4:16 pm | Updated March 23, 2023 at 10:39 pm | 7 min read
In a recent conversation with Scott (CID), Ehsan shared his work in the R&D department of True Organic, where he focuses on improving crop vigor by creating a better environment for crops. Specifically, he discussed using rhizotrons to measure and visualize root growth in response to various fertilizer treatments. Although Ehsan encountered some difficulties and limitations, understanding what’s happening below ground is crucial to comprehending crop growth.
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Scott (CID): Ehsan, thank you for discussing your work with me today. Can you give me some background on what you do?
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Ehsan: I work for True Organic in the R&D department. One of the functions that organic fertilizers offers is improving the overall rhizosphere. It doesn’t provide specific nutrients like nitrogen or phosphorus. Instead, our fertilizer is made of several natural raw ingredients, including carbon, which creates a better environment or rhizosphere for crops. Part of that is better soil structure and root and microbial growth.
The fertilizer aims to improve crop vigor, which is especially crucial for crops with a short season (40 days), where plants must establish and grow fast, even when dealing with abiotic or biotic stress.
Last year, I wanted to measure and visualize root growth in response to various fertilizer treatments to see if there is more and earlier root growth. So, we used rhizotrons under field and greenhouse conditions to test different fertilizers. I learned a lot during the discussions with your colleagues, which will help me utilize the rhizotrons more efficiently when I rent them again.
Scott: How did you use rhizotrons? Knowing what you know, how would you move forward, and how would you use it differently?
Ehsan: You know, we rented the rhizotrons. We didn’t buy it. We used them in field conditions in tomatoes, potatoes, and raspberries in different geographies, two in California and one in Oregon, because we wanted in situ measurements. I learned it’s essential to insert the tubes and sleeves correctly; and give them a reasonable amount of time to settle and start having roots around them, to see something. So we had some difficulty, although we gave it about four weeks.
We also ran a trial in the greenhouse where we grew grape root stalks in large five-gallon buckets and inserted the sleeve perpendicularly. Using the rhizotrons in the greenhouse allowed us more treatments out of season.
Scott: Was the four weeks insufficient to get the growth around the tubes to evaluate the figure?
Ehsan: We were meticulous in tightly augering the soil so that the sleeve fits in the whole tunnel without any room around it. I knew that was critical. But one issue was that there were many air pockets. Under the sleeve, there was a large air pocket, covering about 25% of the area. There was also leaking during irrigation so you couldn’t see 360°. But still, two-thirds of the sleeve was in complete contact with soil.
Digging at least two months before scanning is advisable since roots need growing time. In two of our field trials, we saw interesting results. In the potato field trial, where I expected to see more roots, as it is a root crop, we did not see much growth. On the other hand, we saw some root growth in the greenhouse potato trial, but less than expected.
If I repeat this experiment, I would insert those sleeves two months before and allow time post-insertion for roots to develop. And put enough replicates. We had four replicates- because roots can go anywhere. Replications can help if you want statistical analysis, something visual, if you lose samples, or if you don’t see roots; you still have enough samples to say this product or treatment performed better than the others.
Scott: That makes sense. Some of the best results I’ve heard of in using the tool are installations that have been in place for years. It’s given the soil, with irrigation, ample time to settle and the roots to form around the tubes fully. So, generally, the older the installation, the fewer the problems with air pockets. So it’s interesting.
Ehsan: I worked with the lysimeter early on, and it’s the same concept. When you use a plant lysimeter to collect soil solutions, you have to give it a reasonable amount of time until you have complete contact with the lysimeter in the cup. And then, if you have three to five replicates, you see some patterns. So it’s the same.
Scott: What did you find through this study, even with the few difficulties you had? Did any insights come out of it?
Ehsan: We saw results in two of our three field trials. We noticed a positive effect of the fertilizer on tomatoes, as we hypothesized. One tomato trial had replications; the other one was just a demo.
We got the software from a different vendor in Canada due to preference. But in one trial, we did not need measurements from the software because it was apparent visually that there were more roots. And because it takes much time to measure fine roots using the software.
There were some patterns in the other trial with four replicates, but more was needed. The roots didn’t go around the sleeve. In some replicates, you see some roots hitting the sleeve, but not in others. We had rented the tool for only four months. If we owned the instrument, I would have continued the trial for six months to see more roots.
Scott: What’s your background? How did you come to where you are now?
Ehsan: I have a background in soil chemistry. And I’ve been working in organic agriculture and research and development.
Growers care about the yield. What goes on below ground translates into yield. I’m interested in a mechanistic understanding of what’s happening below ground, in the rhizosphere, where you have nutrients, water, microbes, and soil. When you create a better environment, the result is a healthier crop. And the yield is a measure of whether you have a healthy crop.
The chemistry and biology of roots and rhizosphere are important, as is the measurement of roots: growth, distribution, etc. Therefore, I wanted to measure fine-root growth using the rhizotron. But practically, the technology still needs to be improved because of the number of replicates you must use, the cost, and the timing.
Scott: We’re actually in the process of redesigning the instrument. Right now, a cord attached to a tablet is sent down for scanning and lowered farther down to continue to scan deeper. So we’re removing all that and turning the entire device into more of a drone setup where it’s fully cordless and automated. You just put it against the tube, and it travels down the tube and back by itself and then takes an image all the way and stitches it all together for you.
In addition, we’re working with another partner. The project uses machine learning to trace the roots automatically.
Both of those things are huge in terms of time savings. Because you’re not, by any means, the first to mention the amount of time needed is an issue. It has been our goal to reduce the amount of time and effort. There are still some factors; the fact that tubes need to be in the ground for a certain amount of time will still be there.
We are working on a hyper-spectral image as well. And so, not only will it be Vis, but we will also be using NIR to fluoresce different aspects of the root. So I’ll keep you in the loop.
Ehsan: Thanks. The below-ground growth is bulky for plants like tomatoes or corn, even considering the root size. When we core and put the sleeves, you measure a tiny fraction, less than 5% of the total area where roots are distributed. And that makes it tricky unless you have multiple replications. When you look at the differences between treatment A versus B, you are talking about one source of nitrogen versus the other and not nitrogen addition versus none. These differences are acceptable. These differences are reflected in the yield, but measuring differences in small volumes of roots you’re in contact with is challenging.
Having larger cores is challenging; obviously, it would be very destructive and unrealistic. The only way is to have more replications, especially when working with larger bushes of raspberries, whose roots cover quite a large area, 2-3 feet on each side.
I think rhizotron is a good concept. But operating it takes much effort.
Scott: Yeah, you’re right there.
The most successful installations were at the University of Florida, where we do a lot of work. They conduct much research in orange groves. And they have something like 300 or 400 tubes in the ground. So, they have dealt with that challenge. You’re only getting a fraction of plants’ or trees’ root measurements. They’ve dealt with that by just putting more tubes in the ground and having more replications. So, yeah, it has limitations. But, you know, there are always limitations.
Ehsan: Yeah. But that’s an excellent method. It’s very innovative. We will only know a little about roots if we evaluate them; rhizotrons are non-destructive, so it’s still tremendous progress. It’s just as complex as a routine analysis. So it’s more suitable for focused research.
Scott: Is it true that bigger roots, more roots, and more root vigor translate to more yield?
Ehsan: We were interested to see if plants have more roots, which means more capacity to absorb nutrients and water. Or more vigor, where growth is slow. For example, in Central Valley, where we have heat stress, and plants have faster root growth, they pass that early stage of plant development sensitive to heat. Or in the Central Coast, plants have more roots to overcome chill stress. More roots absorb more nutrients and water and make plants more resistant.
The idea was to see either more roots or post-planting weekly for more root vigor.
Scott: What is the goal of instilling more root vigor? Does vigor translate directly to yield, or is it that vigor translates to more stress resistance, leading to less loss and greater yield in the long term?
Ehsan: In our case, vigor was mostly a positive stress response. This could be due to diseases like nematodes, heat, and chill stress. Due to higher vigor, plants pass the ultra-sensitive early stage when they have established roots. After two months, this better root growth allows more water and nutrient capture to give more capacity.
Scott: Interesting. And what do you have coming up? Any new exciting projects?
Ehsan: We’re developing next year’s projects and may use rhizotrons again. I’m still figuring out the research direction and if we will focus on root and more mechanistic understanding.
I learned from our experience and feel more confident now. It depends on whether I will use this technique to evaluate root response. And if I want to use this technique, time will be one of the requirements.
Scott: Well, that’s awesome. You answered all my questions. So thank you so much for the time. I appreciate it.
Ehsan: Thank you. Have a good rest of the day.
Scott: All right. Thanks. See you.
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