Eco-update

U of I Study: Corn-Rye-Soybean-Wheat-Soybean Rotation Reduces Soil Nitrate Losses, Maintains Crop Yields

A nine-year study — comparing a typical two-year corn and soybean rotation with a more intensive three-year rotation involving corn, cereal rye, soybean and winter wheat — found that the three-year system can dramatically reduce nitrogen in farm runoff without compromising yield. The findings are detailed in the journal Frontiers in Environmental Science.

“For maximum crop production we need artificial drainage, in the form of tiles and ditches, across much of Illinois. Unfortunately, nitrate can be lost from the rooting zone with tile water,” said Lowell Gentry, a researcher at the University of Illinois Urbana-Champaign. From 2015 to 2023, the researchers determined crop yield and monitored nitrate loss from tile-drained fields on a working farm. Their “control treatment” consisted of two conventionally managed fields under a corn and soybean rotation. The more intensive three-year crop-rotation system was employed on an adjacent field. This field was planted with corn, followed by a full season of soybeans, then winter wheat. A summer harvest of the wheat was followed by a second crop of soybean the same year, or double-crop soybean. Between corn and soybean, a winter cover crop of cereal rye was grown to protect the soil. The cereal rye was terminated with herbicide prior to soybean planting and allowed to decompose on the soil surface, delivering nutrients to the next crop.

A key difference between the rotational systems was the amount of tillage. The control fields were fully tilled in the fall and spring, but the researchers strip-tilled only a narrow swath of the cornfield in the three-year rotation, minimizing the area tilled to one-third of the total field every third year. “By strip-tilling only about a third of the soil at a time, it takes us nine years to fully till the field,” Gentry said. This enhances soil stability.

Crops like cereal rye and winter wheat are planted in the fall after corn and soybean crops are harvested. These crops keep the soil intact, helping reduce erosion and nutrient runoff, Gentry said. Tilling the soil and leaving it bare for the fall, winter and spring increases soil erosion and boosts the growth of oxygen-loving microbes that consume soil-organic matter, releasing more nitrate.

Growers, policymakers and scientists have spent decades looking for ways to reduce the loss of nitrate from agricultural lands. Some approaches involve using woodchip bioreactors or installing wetlands to capture the runoff. But those approaches mean growers lose the fertilizing power of the nitrate.

“It’s very expensive to make fertilizer, and so I think it’s much more strategic to try and conserve the nitrogen, meaning keep it in the field — don’t let it leave in the first place,” Gentry said. “And that’s what the cereal rye and the winter wheat can do. They suck up enough nitrogen during the fall, winter and spring to lower the soil nitrate level. That reduces the tile nitrate level.”

The researchers saw a 50 percent reduction in tile nitrate losses in the three-year rotation when compared with the normal rotation. This was accomplished without compromising yields, the team found, and early indications are that the economics of the two systems are comparable.

One year during the long-term experiment, wet weather prevented early termination of the cereal rye cover crop, allowing it to grow too tall. The added biomass reduced tile nitrate runoff by 90 percent — a positive outcome — but the excess rye also undermined soybean productivity, lowering yields by 10 percent that year. Another year, an early killing freeze of the double-crop soybean reduced crop yield and increased tile nitrate loss the next spring.

Gentry also noticed over time that the conventionally managed fields sometimes held standing water after heavy rains, while the experimental fields did not. “I think that’s the result of much less tillage in the experimental field, and the fact that earthworms are now abundant in the diverse crop rotation,” he said. “It’s interesting to note that both rotations used a conventional herbicide regime, so we know it’s not the herbicides that kill the worms; it’s the tillage.”

Ideal Nitrogen Fertilizer Rates in Corn Belt Have Been Climbing for Decades The amount of nitrogen fertilizer needed to maximize the profitability of corn production in the Midwest has been increasing by about 1.2 percent per year for the past three decades, according to new Iowa State University research.The study, published last month in Nature Communications, analyzed data from prior long- and short-term studies by Iowa State and the University of Illinois to calculate the Corn Belt’s steadily rising optimum nitrogen rates, which researchers had thought were static over time despite year-to-year fluctuations. Authors of the study primarily attributed the increase in optimum nitrogen rates from 1991 to 2021 to increased loss during wetter springs and the nutrient demands of higher yields, which also rose about 1.2 percent per year over the same time span.

Overuse of Rootworm-resistant Corn Reduces Farmers’ Profits An analysis of data covering 12 years and 10 U.S. Corn Belt states reveals that farmers suffer economic loss from the overapplication of genetically engineered corn designed to combat rootworm pests. The project, published in Science and led by Purdue University entomologist Christian Krupke, documented greater rootworm pest pressure in the western Corn Belt states of Illinois, Iowa, Minnesota, Nebraska, North Dakota, South Dakota and Wisconsin. In these states, farmers commonly plant corn continuously. In the eastern states Corn Belt states of Indiana, Michigan and Ohio, farmers practice crop rotation that reduces the need for control through genetically engineered seed or applied insecticides. However, the use of transgenic corn hybrids targeting rootworm pests has been remarkably similar across the entire region.  BT and antibiotics are both examples of the “biological commons.” Individuals may perceive that it makes sense to use them as insurance, even when risk of harm from the pest seems limited. Farmers thus have tended to use too much of Bt seed targeting rootworms for their bottom-line profit, especially in the eastern Corn Belt. When many growers do this over a long period, though, resistance sets in, and the technology’s decline affects everyone.

Plant Patch Can Detect Stress Signals in Real Time

Early detection of plant stress — before leaves visibly discolor, wilt or wither — is crucial. Researchers reporting in ACS Sensors have created a wearable patch for plants that quickly senses stress and relays the information to a grower. The electrochemical sensor attaches directly to live plant leaves and monitors hydrogen peroxide, a key distress signal.

Pests, drought, extreme temperatures and infections all cause stress in plants. In response, plants’ normal biochemistry gets out of whack, and they produce hydrogen peroxide, which also acts as a signal between cells to activate their defense mechanisms. Early detection of this chemical clue could help people expertly tailor plant care and prevent further damage, thereby maximizing crop yields, even in difficult conditions. 

But most current methods for detecting hydrogen peroxide require removal of plant parts and multiple processing steps or external detectors that observe fluorescence changes, which can get muddled by chlorophyll. And researchers have previously investigated plant-wearable devices to monitor leaf water content as an indicator of plant health. So, the researchers set out to design a stand-alone patch that quickly and accurately detects the hydrogen peroxide distress signals from living plants.

To build a patch that sticks to the underside of leaves, the researchers created an array of microscopic plastic needles across a flexible base. Onto this patterned surface they coated a chitosan-based hydrogel mixture that converted small changes in hydrogen peroxide into measurable differences in electrical current. The mixture contains an enzyme that reacts with hydrogen peroxide to produce electrons and reduced graphene oxide to conduct those electrons through the sensor.

The researchers tested their patches on live, healthy soybean and tobacco plants and compared them to stressed bacteria-infected plants. For both crops infected with the bacterial pathogen Pseudomonas syringae pv. tomato DC3000, the sensor produced more electrical current on stressed leaves than on healthy ones, and the current levels were directly related to the amount of hydrogen peroxide present. The sensor’s measurement of hydrogen peroxide was accurate and confirmed by conventional lab analyses. After about 1 minute, the patches measured hydrogen peroxide in the leaves at significantly lower levels than those previously reported from needle-like sensors for live plants. Patches may be reused nine times before the microscopic needles lose their form.

The new strategy provides information that could help growers efficiently make decisions about their crops, at the current price of less than a dollar per test.

Extending the Survivability of Jug Bugs

Researchers have demonstrated a technique for successfully encapsulating bacteria that can then be stored and applied to plants to improve plant growth and protect against pests and pathogens. The technique opens the door to creating a wide range of crop applications that allow farmers to make use of these beneficial bacteria.

“Many of the beneficial bacteria we know of are fairly fragile, making it difficult to incorporate them into practical, shelf-stable products that can be applied to plant roots or leaves,” said John Cheadle, co-lead author of the paper. “The technique we demonstrate here essentially stabilizes these bacteria, making it possible to develop customized probiotics for plants.”

The new technique utilizes a custom-made emulsion, made from only a handful of ingredients. One part of the emulsion consists of a saline solution that contains plant-growth-promoting bacteria. For the proof-of-concept demonstration, the researchers used the bacteria Pseudomonas simiae and Azospirillum brasilense. P. simiae acts as a biopesticide by promoting pathogen resistance; A. brasilense acts as a biofertilizer by fixing nitrogen.

The second part of the emulsion consists of a biodegradable oil and a biodegradable polymer derived from cellulose. The polymer can be loaded with agrochemical active ingredients, which means the emulsion can incorporate these ingredients without relying on environmentally harmful organic solvents, which are typically used in pesticide formulations.

When the two parts of the emulsion are mixed together, the oil is broken into droplets that are distributed throughout the saline solution. The cellulose polymer sticks to the surface of these droplets, preventing the droplets from merging back together.

Essentially, the emulsion is a salad dressing with the oil droplets held in suspension throughout the saline solution. In practical terms, this would allow the PBPGs to be applied simultaneously with agrochemicals using the same emulsion.

The researchers compared the survival of PBPGs in the emulsion to the survival of PBPGs in the saline solution alone. Samples of each were stored at room temperature. After four weeks, the population of P. simiae in the emulsion was 200 percent higher than the population in saline; the population of A. brasilense in the emulsion was 500 percent higher.

The researchers also demonstrated that the emulsion improved the survival and reproductive success of PBPGs when applied to soil, as compared to applying the bacteria to the soil without the emulsion. 

Iron Oxides Act as Natural Catalysts to Unlock Phosphorus and Fuel Plant Growth

Northwestern University researchers are actively overturning the conventional view of iron oxides as mere phosphorus “sinks.”

A critical nutrient for life, most phosphorus in the soil is organic — from remains of plants, microbes or animals. But plants need inorganic phosphorus — the type found in fertilizers — for food. While researchers traditionally thought only enzymes from microbes and plants could convert organic phosphorus into the inorganic form, Northwestern scientists previously discovered that iron oxides in natural soils and sediments can drive the conversion.

Now, in a new study, the same research team found that iron oxides don’t generate just a negligible amount of the precious resource. In fact, iron oxides are incredibly efficient catalysts — capable of driving the conversion at rates comparable to the reactions of enzymes. The discovery could help researchers and industry experts better understand the phosphorus cycle and optimize its use, especially in agricultural soils. The study was published in the journal Environmental Science & Technology.

“Iron oxides trap phosphorus because they have different charges,” said researcher Ludmilla Aristilde. “Iron oxides are positively charged, and phosphorus is negatively charged. Because of this, anywhere you find phosphorus, you will find it linked with iron oxides.”

The researchers studied the interactions between three common types of iron oxides — goethite, hematite and ferrihydrite — and various structures of ribonucleotides, which are the building blocks of RNA and DNA. They looked for inorganic phosphorus both in the surrounding solution and on the surface of the iron oxides. By running experiments over a specific period of time, and with different concentrations of ribonucleotides, the team determined the reaction’s rates and efficiency.

“We concluded that iron oxides are ‘catalytic traps’ because they catalyze the reaction to remove phosphate from organic compounds but trap the phosphate product on the mineral surface,” Aristilde said. “Enzymes don’t trap the product; they make everything available. We found goethite was the only mineral that didn’t trap all the phosphorus after the reaction.”

Each type of iron oxide exhibited varying degrees of catalytic activity for cleaving phosphorus from the ribonucleotides. While goethite was more efficient with ribonucleotides containing three phosphorus, hematite was more efficient with ribonucleotides containing one phosphorus. Hematite is found in the midwestern part of United States, while goethite is commonly found in soils in the southern United States and South America.