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The latest agricultural advances aren’t always high-tech. On farms around the world, growers are looking to the past for methods that can ensure soil health and bolster yields.
These techniques, such as integrated crop-livestock systems, soil terracing, and intercropping, were invented by long-ago farming societies to maintain fertility and soil structure or increase harvests. For many farmers, simpler methods can be as valuable today as they were in the past.
The latest agricultural advances aren’t always high-tech.
What it is: Allowing livestock to graze on pasture that is later allowed to recuperate and be planted with crops, or grazing crop stubble after harvest. By measuring nitrogen isotopes, a team of archaeobotanists at the University of Oxford found evidence that European farmers as early as 6,000 BCE let their animals reside on areas which, after “natural dung accumulation,” they later planted. Their work, published in the Proceedings of the National Academy of Sciences journal, suggests that farmers learned to domesticate both plants and animals early on, noticing that one pursuit could aid the other by increasing fertility in land where animals had deposited manure.
What integrating crops and livestock does for agriculture: Manure contains nutrients like nitrogen, phosphorus, and potassium that plants need. Manure also contains organic carbon, the basis of the soil food web and the most significant component of soil health.
Why modern farmers are doing this: The practice benefits farmers who both raise herds and farm crops, and are looking to save on purchased fertilizer.
What it is: A physical way of preventing wind and water erosion and keeping soil in place. Terracing is the construction of channels or shorter slopes directly in a field. Inca farmers built millions of acres of terraces on the steep ascents of the Andes mountains back in the 1400s, and the Chinese also used terraces starting around the same time.
What terracing does for soil health: For the Incas, terracing flattened out sections of their mountainous terrains, making them easier to farm. The method also helps conserve water and reduce erosion, which keeps the soil healthy. Terracing is particularly useful in hilly regions—even if not as steep as the Andes—and with soil types or textures susceptible to erosion.
Why modern farmers use terracing: In Western Iowa, the sloping terrain known as the Deep Loess Hills area is home to corn and soybean fields, plus land for hay and pasture. Because of their high silt content, these soils are productive—water drains well in them. But, the loose silt also puts the area at risk of erosion, according to the Soil Science Society of America. Terraces are one way that farmers reduce erosion and slow down water flow in this area, and their efforts proved to be effective, according to a study funded by the Iowa Department of Agriculture and Land Stewardship. They reduced surface runoff and minimized erosion in the period between 2002 and 2008. Along with other conservation practices like no-till and planting grass in waterways, terracing had economic benefits in this region, since the value of soil lost via erosion cost landowners an estimated $6.20 per ton.
What it is: Planting crops nearby or interspersed with one another, often because their nutritional intake and waste output complement one another, but sometimes because of other cooperative qualities. The “three sisters”—maize, squash, and beans—are the most famous example of intercropping and may have been grown together simply because all three are among the earliest domesticated crops grown in Mesoamerica (what is now known as Middle America) between 5,000 and 10,000 years ago.
What intercropping does for soil health: In the three sisters arrangement, beans fix nitrogen by pulling in nitrogen from the air and converting it into usable form in the soil; microbes then digest the nitrogen so that it’s available to the other plants, including the corn and the squash. Corn’s role is to provide trellising for the squash’s vines. And those vines creep over the surface, protecting the soil from erosion and heading off pests that would burrow in. Other complementary crops may contribute different benefits to soil health or to each other.
Why modern farmers use intercropping: To bolster soil health, which can be depleted by growing the same crops again and again. This practice can be used to host beneficial insects, or alternatively, to attract pest insects off of plants. Intercropping can also elongate growing seasons, by planting an early crop with a short time to harvest at the same time as a slower-growing fruit or vegetable. Intercropping can sometimes decrease overall yields, however, and because it’s not always done in neat rows, maintenance can be challenging.
Early farmers used observation and trial-and-error to decide on the most effective techniques for maintaining their soil and improving their crops. Today, agronomists have the ability to test and measure exactly how these age-old methods are helping farms with soil health and profitability. And with ag-tech innovations such as wireless soil sensors making nutrient management easier than ever, more farmers have the ability to experiment with these techniques.
One Hawaiian farmer, for example, is using a $20,000 grant from the USDA’s Sustainable Agriculture Research & Education program to figure out if intensive rotational grazing with sheep and chickens will improve his soil conditions and boost microbe populations. And in a 2017 study on intercropping, researchers measured how sorghum crops in Mali and Niger responded to certain nutrient additions in order to predict how well those crops would perform if intercropped with peanuts. Both sorghum and peanuts are valuable subsistence crops, so learning that they grew better together reduced risks for farmers if they planted only one or the other.