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Daily News Blog

06
Oct

Monoculture Agriculture Leads to Poor Soil Health

(Beyond Pesticides, October 6, 2021) Agricultural soils under monoculture cropping systems are not as healthy as soils with diverse plantings, finds research recently published in the journal Agrosystems, Geosciences and Environment. Soil and soil quality are declining rapidly in the United States and around the world, with recent data indicating that the U.S. Corn Belt has lost 35% of its topsoil. Advocates say it is critical that the response to this problem focus on practices that conserve and improve the soil health by building organic matter and healthy microbial populations. “Understanding the management practices that lead to healthier soils will allow farmers to grow the same crops while reducing costly chemical inputs (fertilizers, pesticides, herbicides) and protecting the environment,” said study coauthor Lori Phillips, PhD.

To investigate disparities in soil health between cropping systems, researchers analyzed a long-term cropping system that includes 18 years of continuously grown soy, corn, and perennial grasses. Each cropping system was evaluated for its bacterial and fungal population, as well as a test called CNPS, which measures the enzymes produced by microbes specifically related to the soil’s carbon, nitrogen, phosphorous, and sulfur cycles. Researchers indicate that these measurements create “a holistic measure of biological activity,” according to a press release. While soil organic matter has long been the standard indicator of soil health, its measurement changes very slowly in soils. The CNPS test, which researchers have found correlates with soil organic matter, helps provide a more detailed snapshot of soil health at a given point in time.

Unsurprisingly, perennial grasses are found to contain the best soil health indicators. Within the perennial grasses, the community consisting of red fescue and birdsfoot trefoil (a legume) was found to contain healthier soil than a system with only tall fescue grass. Both soil organic matter and CNPS activity are higher for the grasses than for the monoculture crops by 2- or 3-fold. Microbial communities are also markedly different between monoculture crop and perennial grass soils. The study notes these perennial systems have much more microbial diversity, over eight times more mycorrhizal fungi, and higher ratios of fungi to bacteria.

The higher ratio of fungi to bacteria is likely indicative of the frequency of plowing in the monoculture systems, which occurred each year after harvest, according to the study. Repeated tillage breaks fungal connections that help stabilize soil, which can lead to worsening soil structure. “Intensively managed agricultural soils, with more frequent tillage and high fertilizer inputs, tend to be dominated by bacteria. In contrast, more sustainable management practices increase the overall amount of fungi in soil,” Dr. Phillips notes.

Both monoculture corn and soy are found to have low soil organic matter and CNPS indicators, and high bacterial counts in their soils. However, the soil in soybean crops are found to be the least healthy. “Many people assume that because soybean is a legume and legumes provide their own nitrogen through nitrogen fixation, that soybean must be healthy for the soils,” said Dr. Phillips, noting that soybeans take up most of the available nitrogen during their growing period. “So, it’s the cumulative effect of smaller roots, less residue returned, and the residue that is returned gets broken down too quickly to be stable.”

Although the authors did not delve into specifics over synthetic fertilizer and pesticide usage on the monoculture sites, prior studies that utilize the long-term cropping systems studied in the current paper indicated the regular use of 28% urea-ammonium nitrate fertilizer, glyphosate, glufosinate, and atrazine (perennial grasses were mowed regularly). All of these products have a strong propensity to harm soil health. A review on glyphosate published in 2017 found risks to soil that include the reduction of nutrient availability for plants and organisms, lower diversity, specifically, reductions of beneficial soil bacteria, increases in plant root pathogens, disturbed earthworm activity, reduced nitrogen fixing at plant roots, and compromised growth and reproduction in some soil and aquatic organisms. Synthetic fertilizers are particularly problematic, requiring high amounts of fossil fuels to produce, and releasing toxic carbon-trapping byproducts into air and waterways after application. Because synthetic fertilizers are in plant available form, whatever is not immediately taken up by a plant most simply runs off through the soil. Microbial populations are likewise harmed by these quick influxes of nutrients, resulting in damage to soil structure, soil diversity, and nutrient availability.  

Poor soil health impacts the ecosystem services that a given area can provide. From decomposition of organic matter to carbon fixation and nutrient cycling, a healthy stock of soil microbes are critical. Research finds that the less diverse soil microbes are, the less functional a landscape will be.

“Agricultural management practices that reduce soil disturbance, reduce chemical inputs, and increase the amount of time the soil is covered by a living crop all contribute to improved soil biological health,” said Dr. Phillips. “Improved soil biological health will lead to more profitable and sustainable farms.”

When deciding how to manage land, whether for a farm, garden, natural land, or right-of-way, it is critical to think holistically about management practices. Working with and mimicking natural processes should be the focus, with product inputs used only to support sustainable cultural practices. Organic agriculture provides a successful framework for this approach, eschewing toxic synthetic products in favor of natural materials that are compatible with organic systems. Research finds that organic production provides multiple benefits to human society, including long-term ecological, public health, and socioeconomic advantages over conventional, chemical-dependent systems that are often monoculture focused and only work at industrial scales.

For more information on creating holistic organic systems, see Beyond Pesticides article in our quarterly newsletter Pesticides and You, Thinking Holistically When Making Land Management Decisions.  

All unattributed positions and opinions in this piece are those of Beyond Pesticides.

Source: Agrosystems, Geosciences and Environment

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