In one of the toughest growing regions in the US, commercial farmers like Frank Machac are experimenting with a style of ancient agriculture more known for soil health than profit. They are perhaps unlikely budding agroecologists. “My number one concern is yield, I’m not worrying about climate change,” said Machac, 60, a ruddy-faced straight talker with 30 years’ farming experience in the Rio Grande Valley (RGV). Machac is among a group of farmers decked in sturdy boots and faded jeans gathered around a mini weather station in a hot and muddy field of sorghum – an ancient nutritious grain grown for cattle field on commercial farms across the RGV. The 400-acre field is part of a real-farm collaborative research project to figure out how – or if – cover cropping, a regenerative agricultural technique, can help commodity farmers become more climate resilient. “If cover crops can make agriculture more sustainable without me losing money, then it can’t hurt, but we have to get it right,” said Machac, who currently rents 3,000 acres across Hidalgo county, Texas. Cover crops are planted between growing periods for cash crops – grains, legumes, vegetables and fruits farmed to sell or eat – to nourish and stabilise the soil rather than leave it exposed. It’s an ancient practice being heavily promoted by the US government, as a way to help 21st-century farmers mitigate and adapt to rapidly changing weather conditions. But cover cropping poses particular challenges in this water-scarce region where around half the farmland depends exclusively on rainfall – and many are climate skeptics. For the past two years, portable weather monitors measuring temperature, rainfall and soil moisture have been collecting data across the field which is flanked by disused oil rigs and mesquite trees. Between July and December, half was covered in iron clay cowpeas and sunn hemp, heat- and drought-tolerant nitrogen-rich legumes, while the other half was farmed as usual – with no off-season cover crop – as a side-by-side control. It is one of four farms in four adjacent counties that are currently enrolled in the study led by Alexis Racelis, program director of the agroecology and resilient food systems program at University of Texas RGV. Racelis and his crew of international students also collect data on yield, nitrogen content, soil stability, pollinators and microbes – good and bad. In November 2022, cattle belonging to rancher and landowner Betty Perez (who rents to Machac) were herded into the fenced research field to chomp on the legumes and fertilise the soil in their own way for about a month. The 30 or so cows and a few calves loved the cowpea, which is around 25% protein, but not so much the sunn hemp – a view shared by Machac, who found its long taproots hard (and expensive) to get rid of. “Never again, I’ll stick to cowpea!” Perez, 74, who was recently forced to sell several cows to make ends meet after a long dry spell sent hay prices soaring, is optimistic about the benefits. “It was an extra field of food, which I really needed … Also these fields have been farmed for so long, it’s ruining the land and we’re losing water because of the erosion. This is exciting, but I know a couple of years won’t solve it.” The study is already at the halfway mark (unless the funding is renewed), and this field day was an opportunity to share the results so far – positive and negative – with the participant farmers, and others considering taking part, as well as USDA officials promoting cover cropping across the region. It’s early days, but the good news so far is that cover crops prevent wind erosion, improve soil health and increase the diversity of pollinators and good microbes. The bad news is that when there’s not enough rain at the right time – as happens frequently in this water-limited region, the legumes steal the scarce water which impacts the cash crop yield. It’s a mixed bag and more regionally relevant data is needed. “The science supporting cover crops in the RGV is very underdeveloped, and we need to change that so farmers know what makes sense for them. How do we help commodity farmers transition to more sustainable techniques in the valley, where water is the number one limiting factor and where conditions are more like Costa Rica than Nebraska?” said Racelis. The RGV is located on a floodplain near the mouth of the Rio Grande, a hot and humid region that stretches across the southern tip of Texas and northern Tamaulipas in Mexico, where the weather is notoriously unpredictable and ultra-localised. Thanks to the subtropical conditions and short mild winter, valley farmers can grow a wide range of fruits (citrus, melons, strawberries, tomatoes) and more than 40 vegetables (onions, peppers, asparagus, cabbage, spinach), as well as commodities like sugar cane, cotton, corn, sunflowers and sesame. In recent weeks some fields in some farms were hit hard by hailstorms, 80mph winds and torrential rainfall – which came after a prolonged dry spell that forced some to delay planting and sell off skinny cattle. Scientists warn that global heating will likely exacerbate weather extremes and soil erosion – a major issue due to the valley’s brutal winds, over-farming and unchecked deforestation. The valley has been getting gradually hotter since the 1980s, but temperature rise has accelerated since 2010 – mirroring global heating trends. In McAllen, the largest city in Hidalgo county, the number of very hot days, when the average temperature hits at least 100F (37.7C), has gone from zero to 26, according to National Weather Service (NWS) data comparing 1981 to 2010 with 1991 to 2020. If the trend continues, modelling suggests there could be a hundred 100F days by 2060. Rainfall patterns are also getting more extreme – from flood to drought and back again – though there’s not quite enough data to attribute this directly to global heating, according to Barry Goldsmith, a NWS meteorologist. Drought poses a problem for all farmers, but particularly for dryland (rainfall dependent) farmers with no irrigation. “It’s dry, it’s hot, it’s unpredictable, this has always been one of the hardest places to farm,” said Hunter Wilde, who farms sugar cane, corn, cotton and grains on 14,000 acres in neighbouring Willacy county. Over the years, USDA programs encouraging farmers and ranchers to reduce environmental harms and integrate conservation into working lands have come and gone with varying success. The latest boost comes via the Inflation Reduction Act which includes $20bn to help farmers implement climate-smart agricultural practices like cover cropping and reduced tillage, and crop rotation to improve resilience to rapidly changing climate conditions – and reduce the sector’s greenhouse gas footprint. Cover cropping was used by farmers to improve soil health in ancient China and India, the Roman empire, and by both Indigenous Americans and the founding fathers – in fact the practice was commonplace in farming globally including the US until the Green Revolution ushered in widespread use of monocrops, synthetic fertilisers and pesticides. It’s the hot new (old) thing, as cover crops sequester carbon from the atmosphere and can boost climate flexibility by absorbing excess water when it rains too much or holding onto it during drier periods. In the RGV, the Natural Resources Conservation Service (NRCS), a USDA agency, can use IRA funds to pay farmers $37 per acre to plant cover crops on up 1,000 acres through 2026 – or a smaller fee to landowners to establish cover crops with renters. But what works in small plots or on large scale commercial farms in the midwest – where the vast majority of American research into cover crops has taken place – is not directly applicable to the very particular conditions of the RGV. Cover crops may be easy to grow in Nebraska and Ohio where there’s plenty of water and the winter freeze will kill them off. But here the water situation is so tight that cover crops can leave cash crops stunted, while the mild winter means termination requires tillage and weedkiller. Still, most farmers want to do better, and Wilby began experimenting with cover crops eight or so years ago after watching a video by Gabe Brown, a rancher and pioneer of the American soil health movement from North Dakota. Soon after he and his buddy Travis Johnson connected with Racelis at UT, and through trial and error figured out that only a handful of cover crops are suitable for the valley’s searing summer heat – and even these need to be planted several inches under the topsoil using modified machinery most farmers don’t have. If farmers terminate the cover crop too late, it could become a weed and steal too much water; if they terminate too soon, they may lose out on nitrogen and other benefits that boost yields and help balance the books. “It’s been a long rough ride and I’ve not seen the benefits so far. I have a duty to take care of the land, but I also have a family to feed and can’t keep haemorrhaging money,” said Wilde, 34, whose experimental field depends on rainfall. “The results have to show higher yields or reduced costs, that’s the bottom line. I am out if this doesn’t work, maybe it’s just time to move onto the next thing.” Johnson urges him to keep an open mind. Five years ago Johnson, 44, planted sunn hemp as a cover crop on one irrigated field, which has consistently produced above average yields (for different crops) ever since. Neither he nor the UT team know exactly why, but access to irrigation likely played a role. “Pretending we can grow the same things in the same way everywhere – whether it’s cash crops or cover crops – is increasingly weird and not working. We need datasets to inform farmers in geographical and climate specific ways, rather than the USDA just pushing cover crops on dry land farmers,” said Stephanie Kasper, a crop scientist with the agroecology program. The UT study, which is funded by the NRCS, pays farmers $70 per acre – twice what they pay farmers directly – though even that barely covers the full costs. So far, cover crops combined with livestock (prohibited for direct NRCS recipients) has produced the highest soil health scores, but it’s too early to make firm recommendations. At 26, Reese Teplicek is a rare thing in the valley, an ambitious young farmer who wants to grow the family business rather than selling out to ranchers or developers. Softly spoken and farm skinny, Teplicek is all in with the study, and has dedicated 500 acres that last season was half-covered with cowpea, sunn hemp and sorghum sudangrass, diverse cover crops, to attract diverse bugs, said Teplicek. The sorghum in the cover crop field is smaller, due to the water guzzled by the legumes, but there are fewer weeds and pests, and more nitrogen in the soil. But the biggest benefit so far has been reduced wind erosion, which usually costs Teplicek 100 acres of crops each year. This farmland was once covered in mesquites and other drought adapted native species, but is now dotted with eroded sandy hills. “I’m too young to know if this is climate change or normal weather patterns, but unpredictability is our biggest problem, and anyone who farms here will tell you that,” said Teplicek, a graduate in soil and crop science. “The more information we have the better, but if the numbers add up, I’ll apply cover crops across the farm. This is a long game, it’s going to take time to improve the soil.”