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The Crop of the Future

Harvesting carbon could offer a solution to climate change.

Whether you call it global warming or climate change, the emotionally charged topic generally associated with greenhouse gases brings an array of reactions – from genuine concern to belief in a conspiracy. Granted, natural shifts in global temperatures have occurred throughout human history. However, the fact remains that Earth’s average surface temperature has increased 1.3ºF. over the past century and is projected to increase by an additional 3.2ºF. to 7.2ºF. over the 21st century. It is happening at a faster rate than ever before.

Fortunately, U.S. farmers and ranchers are poised to make a difference. In fact, they have already adopted technologies in many instances that are helping to slow greenhouse gas emissions – even if it has been inadvertent – in the quest for reduced soil erosion, lower input costs, or improved water conservation.

temperature change is both good and bad

While the global temperature change may seem slight and insignificant, it does pose implications – both good and bad – for farmers and ranchers. According to the EPA, it can lead to a longer growing season in some regions, yet have an adverse effect on crops where summer heat already limits production.

Global warming can also lead to an increase in soil evaporation rates, as well as the chances of severe drought. It’s believed that climate change may encourage a northern migration of weeds and greater disease pressure in crops and livestock, due to warmer winters and earlier springs.

It’s been well publicized that the temperature rise is attributed to an increase in carbon dioxide and other greenhouse gases that collect in the atmosphere. Although carbon dioxide (CO2) and certain other gases are always present and critical in the atmosphere, an unnatural increase leads to a warming effect that is similar to that found inside a greenhouse. Hence, the term greenhouse effect.

all-of-the-above approach

According to Dan Kane, a doctorate student at Yale University’s School of Forestry and Environmental Studies, who is researching carbon cycling and the role of soil carbon in agriculture, the primary greenhouse gases associated with agriculture are carbon dioxide, methane (CH4), and nitrous oxide (N2O). Although carbon dioxide is the most prevalent greenhouse gas in the atmosphere, methane and nitrous oxide have much longer durations and absorb more long-wave radiation. Fact is, the comparative impact of methane is 25 times greater than that of carbon dioxide, while nitrous oxide has a global warming potential that is around 300 times that of carbon dioxide.

“There are numerous management strategies for drawing carbon out of the atmosphere and holding it in the soil,” says Kane. “In general, they include reducing tillage in order to decrease the level of soil disturbance, practicing crop rotation and rotational grazing, incorporating nitrogen-fixing crops, and using cover crops. They all sort of focus on getting more plant biomass back into the soil and disturbing the soil less. However, going forward, I think we’re going to have to take more of an all-of-the-above approach.”

modified practice

Globally, soils are estimated to contain approximately 1,500 gigatons of organic carbon to 1 meter in depth – more than the amount in vegetation and the atmosphere combined.

Carbon sequestration, meanwhile, is the process involved in carbon capture and the long-term storage of atmospheric carbon in the soil or other carbon sinks. In effect, modification of agricultural practices is one of the most recognized methods of carbon sequestration, as soil can act as an effective carbon sink offsetting as much as 20% of carbon dioxide emissions annually. Reducing tillage reduces soil disturbance and helps mitigate the release of carbon to the atmosphere. Carbon dioxide is just one of the three gases attributed to agriculture. Some of the methane and much of the nitrous oxide in the atmosphere also come from agriculture. While methane emissions are often associated with livestock and the decay of organic waste in landfills, they’re also emitted from wet soil, particularly rice fields, which are typically flooded.

“One positive impact farmers can make is to manage irrigation applications in relationship to crop needs and install or maintain soil drainage systems,” Kane notes.

Still, methane accounted for only about 10% of all U.S. greenhouse gas emissions from human activities in 2015. Even though CO2 accounted for about 82.2% of all U.S. greenhouse gas emissions from human activities, only about 8% of it came from agricultural activities. That’s not the case with nitrous oxide emissions.

Although some of it is attributed to fuel combustion and industry, up to 75% of N2O emissions in the U.S. are attributed to the addition of nitrogen to the soil through the use of ammonia and urea-based fertilizer and inefficient soil management, which results in nitrogen volatilization. Fortunately, precision farming and advanced technology have the potential to significantly reduce that figure, as well. A Georgia study, for example, estimates that a cover crop of rye captured from 69% to 100% of the residual nitrogen left after a corn crop.

“If you look at it globally, nitrogen-use efficiency is still less than 50%,” says Raj Khosla, professor of precision agriculture at Colorado State University. “Fortunately, we have much of the technology and knowledge we need to change that number.”

the 5-R strategy

To do that, both Khosla and Kane advocate the adoption of the five R’s of nitrogen management, which involves using the right fertilizer source, at the right rate, at the right time, in the right place, and in the right manner. In other words, is the fertilizer type and amount matched to the crop’s needs? Is it applied when the crop needs it? Are nutrients placed where the crops can use them?

“When I get up in the morning, I certainly don’t eat all three meals for breakfast,” he muses. “Yet, we feed a 100-day crop at the beginning of the season. It’s much better for both the crop and the environment to feed the crop as it needs it.

“Certainly, one size doesn’t fit all,” Khosla continues, noting that there is a wide array of tools farmers can use to meet what he calls his 5-R strategy. They include GPS guidance and variable-rate fertilizer application to avoid overapplication, the use of center pivots for fertigation at different stages of crop growth, side-dressing standing corn with drop nozzles on crop sprayers, and banding fertilizer with the planter.

“At the same time, we have a lot more tools for sensing the need for nitrogen than we did 10 years ago,” he says. “A network of service providers is already employing satellite imagery to provide customers with a fertilizer prescription map.”

Drones with cameras can also give farmers a spectral signature to quantify the what, where, when, and how much for fertilizer application. Both Khosla and Kane point to the use of crop color-sensing systems, such as OptRx, GreenSeeker, and CropSpec, as tools for spoon-feeding fertilizer to the crop. All three systems use optical sensors to measure and quantify crop health or vigor via leaf color and to provide instant rate adjustment when coupled to variable-rate controllers.

“It’s one thing, though, to pick up the spectral signature, but it’s quite another to translate that into the number of pounds per acre the farmer should apply at a particular stage in time,” Khosla says. “We’re still working on that, while developing tools to measure both carbon and nitrogen in the field without taking soil samples to the lab.

“In the meantime, it’s encouraging to see more farmers practicing the 5-R program,” he says. “The challenge is to get everyone on board, particularly when farmers in other parts of the world are still broadcasting fertilizer, which exposes it to volatilization from day one.”

what’s it worth?

The irony is that the same farmers who provide the world with their food and fiber may be the same ones who help slow/reverse the effects of temperature change. To date, the only viable way to trap atmospheric carbon dioxide is through photosynthesis, in which CO2 is absorbed by plants and turned into carbon compounds for plant growth. Hence, carbon may become the crop of the future for American agriculture. Now it’s up to the public sector to decide what it’s worth and to engage farmers in greenhouse gas reduction.

5 strategies to draw carbon out of the atmosphere and hold it in the soil

  1. Reduce tillage in order to decrease the level of soil disturbance that releases the carbon back into the air. “When aggregates remain stable and undisturbed, they can protect soil carbon for very extended periods of time. However, tillage can quickly break apart aggregates, exposing soil carbon to microbial attack,” says Dan Kane, a doctorate student at Yale University’s School of Forestry and Environmental Studies.
  2. Practice crop rotation. “Periodic green fallows, winter cover crops, and crop rotations that utilize semiperennial crops such as alfalfa, were practices long used in agriculture that fell out of use, as synthetic fertilizers and pesticides became more widely used. Such practices have demonstrated benefits for weed suppression and soil fertility, and some evidence suggests that they can also lead to carbon sequestration,” he says.
  3. Graze in a rotation. “When managed correctly, herds of grazing animals can maximize annual pasture biomass production and redistribute carbon in the more processed form of manure, leading to rapid increases in soil carbon. Methods such as Management-Intensive Grazing emphasize frequently moving cattle to new pastures, having high stocking densities, and preventing overgrazing,” Kane says.
  4. Incorporate nitrogen-fixing crops. “Introducing plant diversity to crop rotations and using legume cover crops, which contain carbon compounds likely more resistant to microbial metabolism, could also increase the complexity and diversity of soil carbon, making it more stable,” he says.
  5. Use cover crops. “Soil carbon sequestration involves transferring atmospheric carbon into the soil via plant photosynthesis and keeping those soil-based carbon pools protected as effectively as possible from microbial activity,” Kane says.
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