Credit: Courtesy St. Martin's Press. Copyright 2016.
Excerpted from Water in Plain Sight: Hope For A Thirsty World by Judith D. Schwartz, with permission from St. Martin's Press. Copyright 2016.
The Chemistry Of Bumper Crops
Judith D. Schwartz
When it comes to irrigation, water is not simply water.
This is dogma to John Kempf, an Ohio farmer who has made a career of improving crop health and agriculture yields. In 2006, Kempf founded the company Advancing Eco Agriculture, a consulting service for farmers that provides testing and analysis of crop specimens and recommends various plant nutrition treatments to improve crop yields.
The sources of water used for crops—be it well, river or reservoir—vary as to the mineral salts that they carry. The degree to which salts are present in water is referred to as “hardness,” generally described in terms of grains per gallon. (“Salt” in this context is not what you’d sprinkle on scrambled eggs, but the combination of elements with a positive charge [cation] and negative charge [anion].) Kempf says that poor water quality, specifically water with high levels of calcium carbonate (lime), is a problem not often acknowledged in public discussions of agriculture—but one that affects crop production and, ironically, leads to a higher use of water.
“The level of minerals affects not only plants’ ability to absorb water, but also how the plant can absorb nutrition,” says Kempf. “Hard water requires more energy, and therefore nutrition, to break it down. When water quality is poor, more water is required.” Farms do regularly test for water quality, and he says that when a potential client’s water source has more than five grains per gallon he recommends that it be treated.
“When farms irrigate with poor-quality water there are multiple effects,” he says. “It ties up all the nutrients that have been applied in the form of fertilizers. It significantly suppresses soil biology. And what often happens is that sodium and calcium bicarbonates accumulate in the soil profile. This leads to salinity.”
By binding nutrients and inhibiting biological processes in the soil, hard water undermines the plants’ ability to reach higher stages of health. This results in less-resilient crops and precludes the water-saving efficiencies that characterize robust plants. Plus, additional water may be needed to correct the problems associated with poor-quality water. For example, soil salinity is typically addressed by flushing the area with large amounts of water. That’s why salinity tends to be a problem in dryer areas like Australia and the northern Great Plains in Canada and the United States. In Vermont, for example, copious rains easily wash out excess saltiness. However, Kempf is not talking only about places like California, where he says the situation is endemic. “Ohio, Pennsylvania and the entire Midwest have this problem,” he says. “But no one talks about it.”
At the close of each growing season, the Advancing Eco Agriculture team gathers for a debriefing. “We sit around as a group and go through our entire list of customers,” Kempf says. “Who got the results that we would have expected? And whose results were we not satisfied with? The farmer might be ecstatic. He might have gotten a 20 or 30 percent increase in yield. But in many cases we may feel there’s still a lot left on the table here, much opportunity for improvement.
“When we went through this process in the fall of 2014, we discovered that there was one common factor among all the farms that, by our standards, were doing poorly. It was that they had poor-quality water. In particular, they were putting on foliar applications [spraying directly on leaves] with poor quality water. Whenever a farmer puts on applications with hard water, particularly water that has bicarbonates, I would say it’s not going to be 100 percent effective.” It’s gotten to the point where the company will not work with clients unless a water quality problem is addressed, he says. “If a farmer wants to work with us and has poor quality water, we will not sell him the product unless he changes the water because we know the program won’t work and that he’ll blame it on us.”
The company sets a limit of five grains of hardness per gallon for foliar water and ten grains for irrigation. “Eighty-five percent of all the water used on farms in this country falls on this spectrum—in excess of five grains per gallon,” Kempf says. “We don’t hear about it in the Midwest because we get rain that flushes the toxins out of the soil. If we did not get rain we would have the same problems as in California to a lesser degree.”
It’s impossible to fully address water quality without discussing nitrogen. According to Christine Jones, a soil ecologist who organizes renowned workshops and conferences on optimizing landscape health and farm productivity, farmers globally apply more than $100 billion in nitrogen fertilizers to their crop fields and pastures each year. Less than half of this is actually taken up by plants. The remainder, between 60 and 90 percent, “is leached into water, volatized into the air or immobilized in soil.” That excess nitrogen will inevitably cause problems. In terms of the atmosphere, increased fertilizer use is associated with the rise in emissions of nitrous oxide, a greenhouse gas with 300 times more impact than CO2. As for water, the USDA’s Economic Research Service estimates that removing nitrates from municipal water supplies costs Americans more than $4.8 billion each year. We can thank excessive use and poor management of nitrogen (and phosphorus) fertilizers for algae blooms and the 6,000-square-mile dead zone in the Gulf of Mexico. Because nitrogen fertilizers are relatively cheap, farmers have an incentive to apply more rather than less. The UN’s Food and Agricultural Organization suggests that nitrogen fertilizer use worldwide will continue to grow, surpassing 200 million metric tons (220 million tons) in 2018.
Jones says the ecological fallout of widespread nitrogen fertilizer use goes far beyond pollution. Inorganic nitrogen alters biological systems in the soil in a way that results in a greater use of water. The problem, as I heard her articulate it at the 2014 Quivira conference in Albuquerque, New Mexico, is that “in pursuit of yield we’ve uncoupled the linkages between carbon, nitrogen and water.”
If irrigation is the story of farming, nitrogen is what drives the story of the green revolution. All living things require nitrogen; nitrogen compounds, such as amino acids, are central to the production of proteins. As it happens, there’s plenty of nitrogen around—it accounts for 78 percent of our atmosphere. However, the N2 gas is very stable, and not available to plants. The nitrogen needs to be “fixed”—its bonds severed—via lightning or nitrogen-fixing bacteria in the soil or in the root nodules of legumes. Usable nitrogen is also present in plant and animal waste, albeit released slowly. Keeping enough nitrogen in the system has been an ongoing challenge for farmers. Most rely on manure, composting, and crop rotation or cover crops, particularly from plants in the legume family, like peas and clovers.
Everything changed in 1909 with the arrival of the Haber-Bosch process, an energy-intensive and high-heat means of synthesizing plant-ready forms of nitrogen from nitrogen gas, literally creating fertilizer out of thin air. The manufacture of nitrogen fertilizer brought about increased crop production, industrial-scale farming operations, and the advent of high-yield plant varieties—all features of the green revolution, which began in the 1940s and both served and propelled the dramatic growth in world population. (The Haber-Bosch technology also facilitated industrial warfare, as it is integral to the mass production of explosives, like mustard gas, nitroglycerin and TNT.)
Jones stresses the difference between organic nitrogen, which is the most prevalent form in natural systems, and inorganic nitrogen, found in synthesized fertilizers. You can tell that plants are nitrogen-deficient when they turn yellow, she says. As an amateur gardener I know this as I sometimes get yellowing with my tomatoes, particularly on the lower leaves. But if I look around now, in early summer, from where I sit on my back deck, I have a panorama of all kinds of trees and shrubs and unstoppable kiwi vines and nowhere do I see the slightest hint of yellow. Somehow, then, these plants around my property are getting their daily dose of nitrogen. Lightning isn’t doled out that evenly, and aside from some clover among the grasses, there are few legumes. So it must be through associations with nitrogen-fixing bacteria.
“I’ve never seen a nitrogen-deficient plant in a natural ecosystem,” says Jones. “Obviously there’s something we’re doing in agriculture that’s interfering with the biological fixation of nitrogen.” Practices that inhibit natural nitrogen fixation include keeping bare fallows, inappropriate grazing, using fungicides and pesticides, and applying high rates of nitrogen fertilizer. She calls nitrogen a “double-edged sword,” as adding it offers apparent results while at the same time disrupting the systems upon which the crops depend. Farms become reliant on synthetic nitrogen to compensate for impaired soil, Jones says; they need to be weaned from it, as from a drug.
The transfer of fixed nitrogen to plants, in the form of nitrogen compounds like amino acids, takes place via the hyphae of Mycorrhizal fungi. The fungi do not themselves fix the nitrogen. Rather, the nitrogen compounds are part of the trading network for which Mycorrhizal fungi often act as broker. In a thriving soil system, plants send carbon exudates out through their roots. These sugars are bartered with microbes and fungi for minerals the plant needs, including nitrogen, often through a Mycorrhizal intermediary.
If we zoom in to the cellular level, we see that nitrogen and carbon are inextricably linked: chlorophyll, where photosynthesis takes place, is part of a protein complex, which means it must contain nitrogen. Therefore, photosynthesis cannot be achieved without nitrogen. At the same time, the plant cannot procure nitrogen without carbon compounds that can be exchanged for it.
In bestowing nitrogen upon plants without asking them to “pay” for it with carbon, we’ve disturbed the arrangement. “When crops and pastures are not performing, we tend to want to add something to the soil to fix it, and that’s usually nitrogen. By using inorganic nitrogen we’re short-circuiting the pathway,” says Jones. “The plant doesn’t need to provide carbon to microbes in exchange for nitrogen, and therefore the plant is not getting the other nutrients the microbes are also providing.”
With no need to deal in carbon, plants get lazy. “Due to the use of synthetic nitrogen, there’s a loss of carbon in the soil,” says Jones. “Therefore the soil no longer has structure, and water-holding capacity is reduced. And because plants are not getting trace elements, plant immunity is down. This leaves them susceptible to pests and disease and now farmers need expensive pesticides. It messes up the food chain. Plus, we need more water because the soil isn’t retaining it.” She stresses that the plants may look just fine—certainly no yellowing since there’s nitrogen galore—but the edifice that supports them is crumbling.
Jones urges us not to underestimate these invisible alliances that she calls, collectively, “the microbial bridge.” “We have to remember that plants can’t move, but they do signal. Minerals are not just floating around in the soil, they are bound up. They need bacterial and fungal enzymes to release them. The plant provides the biochemical energy, the fuel, for these ecosystem processes.” In so doing, the plant helps to build soil.