Plants don’t do this to waste energy, they do it to recruit microbial partners in the
zone around their roots—the rhizosphere. In this life-filled zone, root exudates
nourish microbes that assist the botanical world with nutrient acquisition and
signaling that aids plant defense. A 2016 review in Advances in Agronomy concluded that the plant microbiome was solidly established as crucial for maintaining
plant health in both natural and agricultural systems through its influence on access
to water and nutrients, as well as resistance to pests and disease (Reeve et al. 2016).
Of particular importance is that most terrestrial plants, including humanity’s
primary crops, develop symbiotic relationships with mycorrhizal fungi. Acting as
root extensions, mycorrhizal fungi can take up immobile elements like zinc and
phosphorous from the soil and deliver them to crops (Bolan 1991). The partnerships
can be multidimensional and network communities of bacteria, fungi, and plants into
mutually beneficial exchanges. For example, certain fungi and bacteria in the soil
increase the availability of normally stable elements like iron (Nielands 1995) that
mycorrhizal fungi then help plants take up (Antunes et al. 2012). The foundational
nature of soil life in building soil health was highlighted by the recent discovery that
root exudates are a primary source of soil carbon (Liang et al. 2017).
We’ve also learned that now-conventional practices undermine mutually beneficial relationships in nature’s subterranean bazaar. Farming practices that reduce
fungal colonization include frequent use of phosphorus and nitrogen fertilizers and
frequent disturbance by tillage (Jansa et al. 2006). Field-scale and experimental
studies show that increased use of inorganic fertilizers reduces the abundance and
diversity of mycorrhizal fungi and selects for less mutualistic species (Johnson 1993;
Egerton-Warburton and Allen 2000; Corkidi et al. 2002). Tillage disrupts soil food
webs and fungal networks (Wardle 1995), reducing species richness in the soil and
the overall diversity of soil fungi and bacteria (Anderson et al. 2017). Tillage also
disrupts fungi that help stabilize and maintain the soil aggregates structuring the
porosity that allows water to drain water down into the soil to where crops can take it
up (Ritz and Young 2004; Jansa et al. 2006), instead of the water running off and
stealing away fertile topsoil.
Conversely, farming practices that cultivate mycorrhizal partnerships can
increase crop yields, enhance mineral micronutrient acquisition, and boost resistance
to pests and pathogens. For example, a 2018 comparison of conventionally tilled and
no-till fields showed that over a 12-year period no-till farming increased crop yields,
microbial biomass, soil organic matter, and plant-available zinc in the soil while
reducing runoff, thereby allowing more water to infiltrate into the soil (Nunes et al.
2018). Introducing a cover crop further increased each of these positive effects, as
well as the amount of plant-available iron in the soil. A broader 2016 review of
54 field studies found that less intensive tillage combined with cover cropping
greatly increased mycorrhizal colonization of crop roots (Bowles et al. 2016).
Overall, tillage, fertilization, and crop diversity all influence fungal abundance and
diversity (Verbruggen and Kiers 2010).
Adopting regenerative practices that cultivate beneficial soil life frames a new
paradigm for agriculture rooted in building soil health—in using microbial ecology
to support soil life. Practices based on the three central principles of conservation
198
D. R. Montgomery
zone around their roots—the rhizosphere. In this life-filled zone, root exudates
nourish microbes that assist the botanical world with nutrient acquisition and
signaling that aids plant defense. A 2016 review in Advances in Agronomy concluded that the plant microbiome was solidly established as crucial for maintaining
plant health in both natural and agricultural systems through its influence on access
to water and nutrients, as well as resistance to pests and disease (Reeve et al. 2016).
Of particular importance is that most terrestrial plants, including humanity’s
primary crops, develop symbiotic relationships with mycorrhizal fungi. Acting as
root extensions, mycorrhizal fungi can take up immobile elements like zinc and
phosphorous from the soil and deliver them to crops (Bolan 1991). The partnerships
can be multidimensional and network communities of bacteria, fungi, and plants into
mutually beneficial exchanges. For example, certain fungi and bacteria in the soil
increase the availability of normally stable elements like iron (Nielands 1995) that
mycorrhizal fungi then help plants take up (Antunes et al. 2012). The foundational
nature of soil life in building soil health was highlighted by the recent discovery that
root exudates are a primary source of soil carbon (Liang et al. 2017).
We’ve also learned that now-conventional practices undermine mutually beneficial relationships in nature’s subterranean bazaar. Farming practices that reduce
fungal colonization include frequent use of phosphorus and nitrogen fertilizers and
frequent disturbance by tillage (Jansa et al. 2006). Field-scale and experimental
studies show that increased use of inorganic fertilizers reduces the abundance and
diversity of mycorrhizal fungi and selects for less mutualistic species (Johnson 1993;
Egerton-Warburton and Allen 2000; Corkidi et al. 2002). Tillage disrupts soil food
webs and fungal networks (Wardle 1995), reducing species richness in the soil and
the overall diversity of soil fungi and bacteria (Anderson et al. 2017). Tillage also
disrupts fungi that help stabilize and maintain the soil aggregates structuring the
porosity that allows water to drain water down into the soil to where crops can take it
up (Ritz and Young 2004; Jansa et al. 2006), instead of the water running off and
stealing away fertile topsoil.
Conversely, farming practices that cultivate mycorrhizal partnerships can
increase crop yields, enhance mineral micronutrient acquisition, and boost resistance
to pests and pathogens. For example, a 2018 comparison of conventionally tilled and
no-till fields showed that over a 12-year period no-till farming increased crop yields,
microbial biomass, soil organic matter, and plant-available zinc in the soil while
reducing runoff, thereby allowing more water to infiltrate into the soil (Nunes et al.
2018). Introducing a cover crop further increased each of these positive effects, as
well as the amount of plant-available iron in the soil. A broader 2016 review of
54 field studies found that less intensive tillage combined with cover cropping
greatly increased mycorrhizal colonization of crop roots (Bowles et al. 2016).
Overall, tillage, fertilization, and crop diversity all influence fungal abundance and
diversity (Verbruggen and Kiers 2010).
Adopting regenerative practices that cultivate beneficial soil life frames a new
paradigm for agriculture rooted in building soil health—in using microbial ecology
to support soil life. Practices based on the three central principles of conservation
198
D. R. Montgomery