Does Conventional Fertilizer Harm Soil Health?

Conventional—or synthetic—fertilizers have dramatically increased short-term yields over the past century. But our reliance on these chemical inputs comes with consequences, including polluted waterways, nutrient runoff, and the release of harmful greenhouse gas emissions.

Alongside pesticides, monocropping, and deforestation, conventional fertilizers also contribute to the deterioration of soil health throughout most of the planet’s fertile land, perhaps the most concerning trend in agriculture.

Why Soil Health Matters

Understanding why soil health is important starts with defining what soil health means. A 2022 study succinctly defines soil health as “the capacity of soil to function as a vital living system, within ecosystem and land-use boundaries, to sustain plant and animal health and productivity, and maintain or improve water and air quality.”

Healthy soils aren’t just necessary for the growth of agricultural crops. They also conserve water, limit erosion, encourage ecological resilience and biodiversity, and have a greater capacity to sequester carbon—a powerful tool in mitigating the effects of climate change.

Conventional fertilizers—especially when used in excess—can degrade soil health. This is bad news, not just for crops, but for the air, the water, and the integrity of critical ecosystems.

The Effects of Excess Fertilizer Use

Conventional fertilizers like synthetic nitrogen and phosphate can efficiently boost plant development and total yields. But an over reliance on their capabilities is common. Over-application is often the norm, as farmers prefer to err on the side of too much fertilization rather than too little.  

Unfortunately, too much fertilizer has profound long-term consequences. These consequences include damages to soil quality and structure, changes to soil pH, and disruptions to the nitrogen cycle—all of which negatively impact the soil microbiome by decreasing microbial diversity and making the soil and plants more susceptible to pests and disease.

Damages to Soil Structure

The physical composition of soil plays a key role in the ability of any given soil to sustainably support plant, animal, and microbial life. Soil structure is determined by a complex swirl of variables, including levels of soil organic carbon (SOC), clay, carbonates, and complex biological and chemical processes that bond different soil materials together.

A stable interplay between soil aggregates encourages water retention, efficient nutrient cycling, and optimal root penetration. The overuse of chemical fertilizers, and the intensive, continuous cultivation practices their use encourages, often disrupt this interplay. The mineral salts in these fertilizers accumulate when over-applied, resulting in a compaction layer that increases erosion and runoff while reducing nutrient and water retention in the soil and uptake by plants. 

Long-term fertilizer use also alters soil pH. Changes in soil pH can have a dramatic effect on nutrient solubility—or the ability of plants to actually make use of nutrients present in the soil.

Decreases in Soil Microbial Diversity

Beyond influencing the chemical and structural composition of soil, conventional fertilizers can reduce the diversity and quantity of life within the soil as well. Many of these soil microbes affected are critical in maintaining both soil structure and the long-term productivity of agricultural land.  

The effects of synthetic fertilizers on soil life depends on application rates, soil chemistry, tilling practices, and a multitude of environmental factors. With so many complex variables interacting, the relationship between fertilizer use and soil diversity is rarely clear-cut.

Most often, it is the dose that makes the poison. For example, the overapplication of synthetic nitrogen fertilizer can reduce the abundance of mycorrhizal fungi that help plants with the uptake of critical nutrients like phosphorus and zinc. But most studies suggest that fertilizers do not inevitably degrade soil diversity—as long as they are used responsibly and not applied in excess.

Using Conventional Fertilizers Responsibly

Thoughtful and rigorous approaches to the use of conventional fertilizers are needed to maintain soil health, reduce water pollution and eutrophication, and limit the unnecessary emission of nitrous oxide—a potent greenhouse gas resulting from synthetic nitrogen fertilizer.

Reducing conventional fertilizer use is possible by following 4R, a framework that aims to maximize production and farmer profitability while enhancing the environmental sustainability of our agricultural systems. 

The 4R approach to conventional fertilizer includes applying the: 

• Right fertilizer source at the
• Right rate, at the
• Right time, and in the
• Right place

In contrast to indiscriminately applying fertilizer with little consideration to particular conditions and plant needs, the 4R approach minimizes fertilizer inputs and preserves healthy soils by giving care to site-specific characteristics.

Some key strategies of 4R nutrient stewardship include:

• Considering both naturally available sources and the characteristics of specific products
• Undertaking grid soil samples to facilitate variable rate applications
• Closely matching fertilization timing with planting date, plant growth characteristics, and awareness of deficiencies at particular growth stages
• Pairing conventional fertilizers with synergistic inputs, like microbial inoculants and other plant biostimulants

Soil Health-Promoting Alternatives to Conventional Fertilizers

Although conventional fertilizers will continue to be necessary for sustaining global food production in the foreseeable future, growers can significantly reduce—and perhaps eliminate—their reliance on them through other practices and inputs that are more conducive to sustaining and building soil health.

Cover Cropping and Crop Rotations

Potent conventional fertilizers make intensive, monocultural growing practices viable in the short term. But repeatedly growing the same crops year after year eventually stops paying dividends. Soil health degrades through repeated tilling and diminishes in microbial diversity, which eventually slowsplant growth and affects yields.. More inputs are then needed to achieve the same levels of productivity, and the destructive cycle is accelerated.

Cover cropping and regular crop rotations can help break this cycle, keeping soils healthy and sustainably productive. Cover crops like alfalfa maintain soil structure, fix nitrogen out of the air, and increase microbial activity, while rotating between crops reduces the risk of pests and diseases.

By preserving soil structure, organic matter, and microbial communities, cover crops and regular rotations can reduce levels of synthetic fertilizer required to maintain yields.

Compost

Popular in organic growing systems, compost adds nutrients, organic matter, and a host of beneficial microbes into the soil. While it may not contain the macronutrient levels comparable to synthetic fertilization sources, compost can improve overall nutrient availability and plant uptake—reducing the total need for additional fertilizer inputs.

Plant Biostimulants

Plant biostimulants are any substance or microbe that stimulates a plant’s inherent natural processes to enhance growth. They can improve nutrient uptake and plant stress tolerance, contributing to yield and quality improvements. Popular plant biostimulants range from humic acid, seaweed extract, and silicic acid to a range of beneficial bacteria and fungi.

Plant biostimulants are not fertilizers. Rather, these substances encourage growth by modulating the connections between the plant and the soil. By doing so, they can improve the availability and uptake of nutrients already in the soil, reducing demands for additional fertilizer.

Microbial Inoculants

Several species of bacteria and fungi are considered plant biostimulants. An abundance of these “beneficial microbes” is a marker of healthy soils. They perform an essential role in nutrient uptake, converting nutrients into a soluble form that plants can absorb. 

Growers can use microbial inoculants to introduce these beneficial microbes to the root zone of their crops. Whether in soil, hydroponics, or any other growing system, microbial inoculants will help reduce fertilizer demands while simultaneously improving plant resilience to pathogens and abiotic stresses.

Beneficial microbes and other biostimulants can work alongside fertilizers to achieve synergistic effects. Combining plant-derived fertilizers, like Impello’s Biofuel™ All Purpose Organic Fertilizer, with biostimulating microbial inoculants can potentially eliminate the need for conventional, salt-based fertilizers entirely.

Reducing Conventional Fertilizer Use: Everybody Wins

Reducing our overreliance on conventional fertilizers is only a good thing. Fewer inputs mean lower expenses for growers and fewer detrimental effects on our soil, freshwater, and climate. We have the tools to get there, through both the better management of conventional fertilizer use and continuing to explore the potential of alternative inputs and growing practices that prioritize soil health and long-term sustainability. 

Want to learn more about the beneficial biology of microbial inoculants, biostimulants, and organic fertilizers? Drop us a line at tech@impellobio.com! We’d love to help you in building a soil and planet-friendly nutrition program.  

References

Bronick, C., & Lal, R. (2005). Soil structure and management: a review. Geoderma, 124(1–2), 3–22. https://doi.org/10.1016/j.geoderma.2004.03.005

Hendrix, J. W., Guo, B. Z., & An, Z. Q. (1995). Divergence of mycorrhizal fungal communities in crop production systems. Plant and Soil, 170(1), 131–140. https://doi.org/10.1007/bf02183061

Krasilnikov, P., Taboada, M. A., & Amanullah. (2022). Fertilizer Use, Soil Health and Agricultural Sustainability. Agriculture, 12(4), 462. https://doi.org/10.3390/agriculture12040462

Kumar Bhatt, M., Labanya, R., & Joshi, H. C. (2019). Influence of Long-term Chemical fertilizers and Organic Manures on Soil Fertility - A Review. Universal Journal of Agricultural Research, 7(5), 177–188. https://doi.org/10.13189/ujar.2019.070502

Nouri, E., Breuillin-Sessoms, F., Feller, U., & Reinhardt, D. (2014). Phosphorus and Nitrogen Regulate Arbuscular Mycorrhizal Symbiosis in Petunia hybrida. PLOS ONE, 9(3), e90841. https://doi.org/10.1371/journal.pone.0090841 

Sun, R., Zhang, X. X., Guo, X., Wang, D., & Chu, H. (2015). Bacterial diversity in soils subjected to long-term chemical fertilization can be more stably maintained with the addition of livestock manure than wheat straw. Soil Biology and Biochemistry, 88, 9–18. https://doi.org/10.1016/j.soilbio.2015.05.007

Tripathi, S., Srivastava, P., Devi, R. S., & Bhadouria, R. (2020). Influence of synthetic fertilizers and pesticides on soil health and soil microbiology. Agrochemicals Detection, Treatment and Remediation, 25–54. https://doi.org/10.1016/b978-0-08-103017-2.00002-7 

What are the 4Rs. (n.d.). https://nutrientstewardship.org/4rs/ 

Zhang, Y., Li, C., Wang, Y., Hu, Y., Christie, P., Zhang, J., & Li, X. (2016). Maize yield and soil fertility with combined use of compost and inorganic fertilizers on a calcareous soil on the North China Plain. Soil and Tillage Research, 155, 85–94. https://doi.org/10.1016/j.still.2015.08.006