Integrating perennial plants with longer root systems among crops is an agricultural strategy that can simultaneously produce more food, and improve soil quality, said Jerry Glover, a senior sustainable systems advisor at USAID.
Glover delivered his remarks at AAAS headquarters in Washington, D.C., as part of a monthly speakers’ series that features timely topics relevant to science and society. Glover is also a public engagement fellow with the Leshner Leadership Institute, an initiative of the AAAS Center for Public Engagement that trains mid-career scientists to engage with public audiences, and served as a AAAS Science & Technology Policy Fellow.
Agriculture faces a challenging paradox: Too much cropland harms the environment, and too little cannot satisfy the world’s food needs, Glover said. The environmental impact of the agricultural footprint is wide-ranging, and climate change is only exacerbating the problem. Expanding farm land diminishes animal habitats, and reduces water runoff, among other environmental challenges. Farming represents the most significant threat to biodiversity, he said. It can degrade soil quality, too, and that has led to the thinnest, least fertile soils in recorded human history, Glover added.
Still, around 800 million people around the world are classified as urgently hungry, Glover said.
“There are estimates that we will need to nearly double food production by 2050,” he said. More than 100 million additional hectares of cropland will be needed to satisfy this need, Glover said.
To address such competing realities, Glover advocates a strategy known as perenniation that integrates perennial trees and other perennial plants — those that survive from one germinating season to the next — among annual crops, which die off after each growing season. Annual crops contribute heavily to the world food system, with three domesticated grains — wheat, maize, and rice — providing 60 percent of the calories humans consume.
Annual crops are “the cause of many of the problems we see with agriculture,” Glover said.
Jerry Glover displays the 10-foot roots of a perennial big bluestem plant. | Gadi Ben-Yehuda/AAAS
Perennials plants have much longer root systems than annuals, allowing them to reach deeper into the soil, and tap more nutrients.
Long roots, said Glover as he unfurled the 10-foot roots of a native big bluestem plant, are “our terrestrial system’s safety net.”
“This root system allows this plant to convert sunlight and nutrients into plant sugars that it pumps below ground,” and to feed soil microbial communities much further below the land surface. The perennial roots also spend much more time in the soil throughout the year than their annual counterparts, allowing them to use water, nutrients, and sunlight more effectively.
There are several strategies for implementing perenniation, Glover said, including the use of evergreen agriculture: planting perennial trees within a field of annual crops.
Take Rhoda, for example, a farmer in western Malawi, who put evergreen agriculture into practice, adding trees to her maize fields to revitalize her unproductive farmland. The trees and maize complement one another and do not compete for nutrients, Glover said, improving the soil. The richer soil yielded more maize, and that allowed Rhoda not only to feed her family — but the added yield also brought in more money that allowed her to invest in more profitable enterprises like livestock. Rhoda can now use tree leaves to feed her pigs and goats, and animal manure to fertilize her crops. The trees also provide a reliable source of firewood and construction materials close to home, Glover added.
Other perenniation strategies include planting two types of legumes—peanuts and pigeon peas—that complement one another, with the peanuts ready to harvest just as the nutrient-rich pigeon peas are flourishing, Glover said. Studies have shown that this doubled-up legume system benefits the soil by delivering twice as much carbon and nitrogen into the soil, he said.
Glover also detailed a “push-pull” system used widely in Kenya to repel pests. The strategy involves planting desmodium, a perennial legume that stops the eggs of pests from thriving, amid crops and planting Napier grass, another perennial, along the field’s perimeter. Desmodium repels, or pushes, pests away, and the Napier grass attracts, or pulls, pests away from the crops. The strategy also improves nitrogen levels in the soil, Glover said.
The United States has rich soils and farmers produce some of the highest yields with annual crops. For this reason, Glover said he does not see perenniation strategies widely taking hold here in the immediate future. Instead, he sees increasing use in sub-Saharan Africa, where poorer soils are more prevalent.
Yet he called for a 21st century vision for food production. “It behooves us to envision something more than domesticated crops” to supply our food, Glover said. “I’m not ready to say ‘no’ to anything.”
[Associated image: Jim Richardson]