Adam B. Cobb, PhD Oklahoma State University, USA
Humanity is exerting intense pressure on our planet, and many agricultural practices are degrading soil stability and fertility over time. Worldwide, we’re losing soil about thirty times faster than it’s being replaced. As farms are depleted of topsoil and organic matter, increased fertilizer inputs are required to maintain crop yield, while mounting fertilizer costs are disproportionally affecting farmers in developing countries. I have witnessed these daunting issues in Africa and Central America, but there is hope.
Our research is part of the Brown Revolution, which seeks to harness the benefits of living soil to sustainability provide nutritious food. In one teacup of healthy soil there are enough arbuscular mycorrhizal (AM) fungi to stretch across 30 football fields. Mycorrhizas partner with the majority of plants, including most agricultural crops, to enhance plant nutrient and water uptake. These fungi also help ensure ecosystem health by limiting fertilizer runoff (eutrophication), reducing soil greenhouse gas emissions (climate change), and stabilizing soil structure (erosion).
We assessed sorghum and cowpea genotypes for responsiveness to AM fungi in low fertility soil and how that symbiosis benefited seed (grain) nutritional contents, such as protein, zinc, and iron. The highly responsive crop genotypes produced around 200% more vegetative biomass and nearly 300% more grain compared to the less responsive genotypes. Furthermore, the average protein production of highly responsive genotypes increased more than 300% compared to the less responsive genotypes grown under the same conditions. Total grain zinc and iron content was also significantly correlated with AM fungal root colonization.
We then investigated the effects of alternative fertility inputs (compost & biochar) on the productivity and nutritional quality of highly mycorrhizal responsive sorghum and cowpea. Compared to plants grown with typical commercial fertilizer rates, plants grown with a blend of biochar, worm compost, and 50% less fertilizer produced similar plant biomass after 45 days of growth, with equal or greater tissue protein, iron, and zinc, significantly higher tissue phosphorous, and 30% more AM fungi in the host plant’s roots. These results indicate biochar and worm compost can boost belowground symbiosis with AM fungi, resulting in increased fertilizer use efficiency. These soil amendments can be produced at various scales, with potentially lower cost than commercial fertilizers, and can enhance soil carbon sequestration.
Nearly 30% of our population urgently needs more dietary protein, zinc, and iron; our results indicate that AM fungi improve both soil health and human health. Furthermore, farming costs and environmental fallout from nutrient pollution can be reduced by managing agroecosystems to encourage abundance and benefits of AM fungi. By encouraging these belowground and aboveground linkages, including the combination of crop genetics, alternative fertility amendments, and improved farm management may help regenerate our soils and nourish our growing population.