Agriculture has been practiced by humankind for over 6000 years, and some of the ancient Sumerian fields are still growing grain. We, as a species, are capable of farming sustainably. Unfortunately, most of the ancient techniques have fallen by the wayside in favor of increased yield and increased profit, with the result that the majority of agriculture worldwide is now heavily chemical- and fossil fuel-dependent, requiring around seven units of fossil energy input for every unit of food energy produced.
In recent years, demand for healthy, local produce combined with a back-to-the-land ethic among young farmers has spurred a movement away from industrial agriculture and toward farmers’ markets, CSAs, and local food production. Organic farms are springing up like weeds these days. I take heart to be a part of this phenomenon, lending my mind and my labor to working the earth, planting the seeds, keeping the water flowing, and gathering the harvest. We still have a long way to go, however. “Sustainable” agriculture aims to sustain the health of the soil, the nutritional value and purity of the food, and the livelihoods of its workers. These are all noble goals, but the question must be asked whether the three principles of sustainability, namely resilience, closed-loop flows, and energy from the sun, are adequately addressed.
Resilience
Agriculture must be able to withstand the vagaries of weather and the biosphere: droughts, floods, cold snaps, heat waves, insects, and diseases. These forces have shaped all life across evolutionary history, with genetic diversity allowing for adaptation. For resilience in agriculture, this genetic diversity is critical. Within a diverse population of, say, kale plants, some will be more frost tolerant. Others will be less palatable to aphids or flea beetles. Still others will stand strong against a new fungal disease. The aim of the traditional art of plant breeding is to select for the most important traits (e.g. frost tolerance, tenderness, flavor) while preserving a diverse population ready to be selected in new ways in response to new challenges.
This approach has largely been abandoned in favor of hybrid vigor and uniformity. Plants are selected for maximum yield, with inbred, genetically-uniform lineages maintained and crossed annually for hybrid seed. The hybrid approach produces more food in the short term, but at the cost of adaptability. Plants have been coevolving with insects and diseases for millions of years, with each side always making minor adaptations to gain the upper hand. Hybrids essentially “freeze” plants in time, eliminating the genetic variability that allows for evolution. Over time, these plants become more susceptible to insects, disease, and environmental stresses, at the same time becoming more dependent on chemicals, fertilizers, and irrigation.
Much of organic, “sustainable” agriculture still plants uniform hybrids, but there is a growing movement toward open-pollinated, locally-adapted varieties. Heirlooms are all the rage, and new open-pollinated varieties are being developed and released. One acre of seed can plant many thousands of acres of vegetable or grain, so I am heartened to see the value of diversity recognized and embraced among seed growers.
Closed Loops: The Problem of Poo
Organic farms are proud of their compost. They make it by the truckload and apply it by the ton, creating fertile soil without the anhydrous ammonia and inorganic minerals used by conventional farmers. Organic farms are good at composting all of their cover crops and on-farm waste, but these supply less than half of the demand with the remainder supplied by manure. The typical nutrient flow of an organic farm thus starts in a field of hay (often with chemical fertilizers) and flows through cattle, manure, compost, soil, crops, food, and finally people before ending up in human pee and poo. And there it stops, since none of that pee or poo ever finds its way back to the fields, ending up instead deep underground in septic tanks or released into rivers through sewage treatment plants.
Here is where organic and sustainable part ways, as organic standards do not allow for the use of “humanure” (composted human waste). This is in part because of fears of pathogens like E. coli and in part because the only large-scale source of humanure – treated municipal sewage – also contains any chemicals, medicines, and heavy metals dumped down the drains. This will be a hard nut to crack, but an essential one nonetheless. Global supplies of phosphorus, an essential plant and human nutrient, are running low, as the supplies present in the soil and mined fertilizer get a one-way ticket to groundwater and the ocean where recovery is all but impossible.
Global human metabolism is 0.7TW, while global agricultural photosynthesis is around 7 TW. This means that 1/10 of the energy in agricultural crops ends up cycling through human bodies. As most living cells contain energy molecules (carbohydrates, lipids, proteins) and mineral nutrients in equal proportion, we can further infer that at least 1/10 of the phosphorus, potassium, sulfur, and magnesium taken up by the crops travels through human bodies and is effectively lost. This is unsustainable on the scale of several years without external inputs and on the scale of decades to centuries with mined minerals. We may have more time to solve the crisis of agricultural nutrient cycling than we have to transition to sustainable energy, but sooner or later if humans are going to survive on this planet we are going to need to return our pee and poo, and the minerals therein, to the soil where our crops are grown.
Sustainable Synthetic Nitrogen?
Nitrogen, as the nutrient most in demand by plants, deserves special mention. Organic standards prohibit synthetic nitrogen application, so nitrogen is supplied by a combination of nitrogen-fixing legume crops and manure application. Unlike phosphorus, nitrogen is abundant making up 78% of our atmosphere, and the limiting step is the energy-intensive conversion (by either biological or chemical methods) to the nitrate form that plants can use. In the natural process, plants exude sugars through their roots to symbiotic bacteria. These bacteria metabolize the sugars, feeding the resultant energy to a nitrogenase enzyme that converts atmospheric nitrogen gas to ammonia, which is then converted and supplied to the plant. In the synthetic process, natural gas (representing 1-2% of global energy use) is converted to hydrogen, and the hydrogen is then reacted with atmospheric nitrogen in the presence of a catalyst to produce ammonia. This reaction, named the Haber-Bosch process, is at the core of fertilizer production and may well be essential for the sustenance of human populations at current levels.
The only major energy input to this process is the creation of hydrogen, and it turns out that hydrogen is relatively easy to make from sustainable electricity. Simply running electricity through water – with the right catalysts – will split water into its hydrogen and oxygen component gases. As wind and solar power gain traction, this type of hydrogen production is emerging as a way to use surplus electricity when intermittent generation exceeds demand. It is quite possible for hydrogen produced in this way to replace fossil hydrogen in the Haber-Bosch process, allowing this reaction to continue to provide soil fertility in a post-fossil-fuel, sustainable world.
Sustainable Energy on the Farm
It’s a dirty secret of small organic farms that they burn a lot of oil. Synthetic fertilizers and pesticides account for around 30-40% of energy use on conventional farms, so this amount is gained. However, some of this is lost as organic farming involves a lot of vehicle miles. An industrial-scale corn farmer will visit a field four times a year to disc and plant, spray, harvest, and plow. An organic market farmer still has those at least that many steps, with cultivation replacing spraying. However, with crops planted in succession, a vehicle needs to return to the field every few days during harvest season, almost always carrying less than a full load. Trucks drive to markets and deliveries at less than full capacity. Trucks shuttle back and forth hauling manure from feedlots, and tractors and front-end loaders turn the compost piles several times. Will small blocks to till, tractors spend proportionally more time driving around and less time working the soil. When you add in the fact that lettuce and tomatoes yield a lot fewer calories per acre than corn, organic vegetable farms can actually use more fossil energy per calorie of food produced than a conventional Midwestern cornfield.
The problem here is that organic agriculture is in competition with industrial agriculture. Consumers will pay more for organic, but only up to a point. Conventional agriculture is effectively subsidized by cheap fossil energy, and so organic agriculture simply cannot compete on a cost basis without applying this same subsidy.
There are no easy solutions. So long as our entire society is based on fossil energy, so too will be any project of that society. There are options: farms designed on a hub and spoke model with walkable scale, solar panels or wind turbines charging electric tractors, biodigesters turning farm waste into fuel. Farming seldom generates the kind of cash needed to make these changes, but in my view organic agriculture cannot call itself sustainable if it does not take steps to decrease or replace fossil energy use.