On Dec. 11, 2020, President-elect Joe Biden announced his nomination for Secretary of Agriculture, and in doing so announced his plan to make U.S. agriculture the first in the world to achieve net zero emissions by paying farmers to put their land in conservation and plant cover crops.
These plans represent an awareness of the importance of soil as the primary source of food (99.7%) for our quickly growing species as well as many others. Soil is also the most significant store of carbon in the world.
As such a critical source of life, the success of civilizations and many species have been determined based on the health of the soil. This is because, even with native vegetation, soil is a virtually non-renewable resource that grows very slowly through the decomposition of organic matter.
Unfortunately, a 2006 meta-study concluded the world is losing soil 10-40 times faster than the natural replenishment rate. Additionally, as a result of this soil loss, 30% of the world’s arable land has become unproductive in the past 40 years.
Thankfully, studies have also shown that conservation agriculture — made possible by relatively modern technology, can completely stop the loss or even regain the soil — while increasing yields in the long-term.
In addition to the source of food for the planet, studies show that soil is a store of carbon which is 3.1 times greater than the total carbon found in the atmosphere. Soil even sequesters carbon faster than the oceans at a rate of 3 to 2 gigatons per year respectively.
But in just the last 200 years of agriculture, humans have contributed 50-100 gigatons towards the total 800 gigatons of carbon in the atmosphere from releasing organic carbon stored in the soil. This is a result of less plant roots and residue in the soil, as well as accelerated decomposition and increased soil erosion as a result of tillage and agriculture.
Therefore, soil plays a crucial role in mitigating the existential threat our world is facing through climate change and potentially an insufficient food supply in the coming decades. As will be explained, innovative, win-win solutions can be found by valuing the health of our soil.
For crop production, the two primary practices of conservation agriculture are no-till and cover crops. No-till is a farming practice which does not disturb the soil and, over time, builds the soil biology such as roots, fungi and earthworms, is shown to reduce erosion by 86% and increase soil organic matter.
For decades scientists have recommended no-till to reduce greenhouse gases (GHGs) due to the enhanced carbon storage in the soil through this increase in organic matter.
To illustrate, a global meta-study looked at the CO2 equivalent of soil carbon (20 cm depth), also considering methane, nitrous oxide, farm operations and inputs, and found that the net GHG emissions per unit of yield decreased 71% in no-till vs conventional tillage systems.
According to the data, over the 20-year period this equates to 1.06 tons of CO2eq per acre per year as a result of total farm efficiency and carbon sequestration.
However, some scientists have challenged whether soil carbon actually increases under no-till systems under all conditions when taking into account carbon deeper in the soil profile (20 cm or more), where plows and other tillage equipment may work to deposit carbon.
A 2019 meta-study published in Nature evaluated just the change in carbon, which included deep in the soil profile (60cm) and found that carbon did increase in all soil types under no-till systems, however for some conditions, not enough for a statistically significant conclusion. The conditions of statistical significance ( warm or temperate moist climates, among others), equated to 0.11 to 0.22 tons per acre per year of carbon sequestration.
The review stated that there is still insufficient data available, especially deep in the soil profile, to make precise estimates in the change of soil carbon as a result of no-till in all conditions, and that it’s unlikely that sufficient studies will clear this up soon. However, the world may not be able to wait for these multi-decade studies to act on the important environmental benefits no-till offers.
The review goes on to explain that no-till has been established worldwide to drastically reduce soil loss from erosion, improve nutrient cycling and capacity, increase water efficiency by reducing evaporation, improve applied nutrient utilization with lower nitrogen runoff levels, and drastically reduce the number of field operating hours and associated fuel use by about 69%.
Therefore, no-till systems are a win-win situation for many of these other policy reasons which effectively reduce global warming potential and environmental damage, with the direct sequestration of carbon being an added benefit.
The main reason why a significant portion of farmers refuse to switch to no-till is likely due to the common initial drop in yield after the first 1 to 2 years of implementation. However, meta-studies focusing on 10 years of no-till show that no-till matched and exceeded conventional tillage after 3 to 10 years of no-till for nearly all climate and crop types.
However, these 10-year studies do not fully capture the important long-term benefits of no-till. A recent 30-year study led by a researcher from Michigan State University stated that despite an initial dip in profits, “for every year for more than 30 years, the yield in no-till treatments increased vs. the yield in tilled ground. I would have expected a point where the yields and economic benefits reached their peak, but they continued to rise. It was jaw-dropping.”
The study stresses the necessity of long-term decadal studies because “the crop yield and soil water availability required 15 years or longer to generate patterns consistent with 29-year trends.”
This yield effect is likely due to the gradual compounding benefits of increasing soil health.
Further to this effect on yield, studies indicate that significant greenhouse gas (GHG) emission benefits do not take place until a decade into no-till for some wet conditions and 20 years for some dry conditions.
Therefore, it would be prudent for governments to subsidize no-till programs, particularly in climates shown to have a relatively strong sequestration response, to counter the initial profitability dip and encourage the reduction in GHG emissions from long-term no-till application.
Perhaps the most important practice of conservation agriculture is cover cropping, which
is a practice of continuously covering cropland with vegetation throughout the offseason (approximately 6 months of the year) with plants that contribute to the health of the soil, rather than leaving it bare.
There are countless different cover crop combinations — each with unique effects. But generally they all act to sequester carbon in soil by breathing in CO2 while alive and serving as organic matter as they decompose, ultimately contributing to the nutrient cycle.
Furthermore, the carbon sequestration potential of cover crops appears to be much higher than no-till, as the cover crops are put to work for half the year doing just that. A study conducted in Ridgetown, Ontario, and recently published in the journal Nature in August 2020, is one of the very few long-running cover crop trials in North America and the first study to look at the profitability of cover crops for farmers, which includes pricing for carbon sequestration.
The study’s results from six cover crop species over 8 years found carbon sequestration of 0.50 to 0.99 tons per acre, per year in the first 15 cm of soil. On a per-cover-crop basis (over 6 crops rather than 8 years), this puts the sequestered carbon at 0.75 to 1.49 carbon tons per acre per cover crop.
Other meta-studies have found sequestration of between 0.044 and 0.45 tons per acre with carbon samples deeper in the soil profile, and 0.45 to 0.67 tons per acre of CO2 equivalent when taking into account total GHG fluxes.
Researchers concluded this has long-term implications on the mitigation of GHG emissions. However, the studies have found that greater crop yields were only associated with vegetable crops (7.9-22% increase) , while grain and oilseed crops yields were not significantly affected, which represents the majority of Canadian cropland.
The researchers state that this lack of immediate yield increase to offset the additional cost of cover cropping is a constraint to their adoption, which is currently relatively low (13.7%). Similar to the compounding effect on soil health observed in no-till, the initial dip in profitability due to the additional cost of cover cropping without an immediate yield benefit represents a barrier to their application.
Furthermore, the long-term use of cover crops is necessary for significant compounding benefits, as meta-studies indicate it takes at least 6 years to detect changes in soil organic carbon, further implying the need for long-term study to appreciate conservation farming benefits.
Meta-studies further indicate a decrease in runoff by up to 80%, sediment loss by 40-96%, improved soil structure, nutrient cycling, compaction, microbial and fungal properties, soil temperature and weed presence.
Other studies have shown a mitigation of 0.06 to 0.21 tons per year of carbon equivalent as a result of favorable albedo change, which is the enhanced reflection of sunlight on the Earth’s surface as a result of cover crops.
But how will it be possible to encourage greater adoption of win-win no-till and cover cropping solutions on a scale and timeframe which will meaningfully respond to climate change? Because for each year of conventional farming it will take 10-40 years of natural replenishment to repair the damage, and — according to a United Nations report — the world’s soil only has 60 harvests left on the current trajectory.
The head of the Biden-Harris review team for the USDA published a memo on the transition and outlined that in the first 100 days of office that conservation farming will be amplified by incentives through the existing crop insurance programs, funding from the USDA conservation program, and the establishment of a carbon bank where carbon credits would be purchased.
Similar programs which reflect the fair value of carbon to farmers must also be implemented in Canada for a timely adoption at scale. Incentives through existing crop insurance programs may be efficient because reporting and auditing processes have been in place for many years through this system.
The target Canadian carbon tax price in 2022 is $55 per ton and rising to $187 by 2030. At $55 per ton compensation, all combinations of cover crops are profitable for farmers.
A study examining how much incentive it would take for farmers in Indiana to make the switch from till to no-till practices found that farmers would make the switch for between $10 and $40 per acre , which falls within the price paid if farmers were compensated for their carbon equivalent sequestration based on the 2022 Canadian carbon tax.
Therefore, such a program would have a practical environmental benefit, and furthermore, it would make sense for compensation to increase with consistent conservation practice to reflect the compounding effect and long-term requirement for many of the benefits.
The initiative could represent a powerful alliance between Canada and the U.S. and set an international momentum towards collaboratively implementing win-win solutions in the fight against climate change, for sufficient food supply and for healthier ecosystems.