Human Water Cycle: Agriculture

Human Water Cycle: Agriculture

It’s how everything from apples to tomatoes to chicken reaches our dinner tables. Agriculture is the practice of working the land to produce crops and raise livestock. And none of it would be possible without water. We as humans just depend entirely on water, and on production, and farm products, and on eating three or four times a day, and all that takes a lot of water. According to the U.S. Department of Agriculture, the United States uses about 80 percent of its freshwater supply for agriculture. In some western states, it’s as much as 90 percent. In addition to using water directly on crops, there are many supporting roles for water in agriculture. This includes livestock production. This includes washing fruits and vegetables. This even includes making fertilizers that you apply to crops. Water and its connection to food and energy is part of something called the human water cycle, which explains how these three vital aspects of human life are reliant upon each other. Meagan Mauter is a professor of Civil and Environmental Engineering at Carnegie Mellon University and is funded by the National Science Foundation. Her research focuses on the connection between water and food. We do work on the supporting systems for agriculture, particularly on how to ensure a sustainable water supply in agricultural systems. Water used in agriculture comes from several sources. It occurs naturally from rainfall, is diverted from rivers and lakes, and is pumped from underground aquifers. Farmers like Cannon Michael of Bowles Farming Company in California’s Central Valley often uses lower quality water that can create a problem called soil salinization. Salt is a naturally dissolved mineral in water. When water evaporates from soil or transpires from plants, the salt is left behind. Salty soil prevents crops from fully taking in water and nutrients, which can lead to smaller crop yields, and even render the soil unusable. And, with 7 billion people on the planet to feed, farmers want to keep agricultural lands healthy and productive. This field here that I’m standing in is a good example of a really bad salt issue. And you can just visually sort of see not only the unevenness of this area here but also a very small plant, compared even to an area just very close by with a much bigger plant with much more cotton on it. Michael uses drones equipped with GPS to gather information about the soil quality on his farm, including the areas suffering from soil salinization. Michael also works with local water managers, like Chase Hurley from the San Luis Canal Company, to figure out how and where the water Hurley provides should be used. The main constituent that we’re concerned about in the water is salt, and so understanding what is being delivered to us is really important. Soon Michael and Hurley may have other tools at their disposal to help fight soil salinization. Mauter and her team are developing a series of small, inexpensive robotic boats outfitted with a variety of sensors to continuously measure water quality in real time. It essentially has sensors on the bottom, computing in the middle, and motors in the back. This data can be used to help farmers decide if they need to modify growing seasons or receive water from a different source. Because each and every farm is a little bit different, the combination of crops and water salinity that they’re applying to those crops differs. Mauter and her team are also looking for ways to desalinate water. One option is a process called capacitive deionization, which uses electricity to separate salt ions from water. You apply an electric field and the ions migrate to that electric field, effectively depleting the salt concentration in the feed stream. Another option is reverse osmosis, where saline water is pumped at high pressure through a membrane that captures salt. MAUTER: We need to really understand exactly how much water a crop needs at a particular moment and how that water need varies across individual plants or across a field, or across an entire region. THOMPSON: Mauter believes all of this research will not only help fight soil salinity, but also help policymakers, water managers and farmers make better decisions about water use, creating a more sustainable human water cycle.

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