Water use is something that both researchers and farmers have explored for decades: what happens to a crop when irrigation is reduced? All backyard gardeners or self-proclaimed green thumb know that plants need water. But how much water is enough? What amount still guarantees healthy plant growth and a good yield of wheat, corn, alfalfa, sorghum, or sunflower? Agricultural engineers are experimenting with new ways to grow more with less water in a process called deficit irrigation: it’s a practice where farmers reduce the amount of water applied to a crop, allowing mild stress to the growing plants.
According to the FAO, irrigated agriculture uses more than 70 percent of the water withdrawn from the earth’s rivers; in developing countries around the world, that figure can exceed 80 percent. In Kansas, irrigation accounts for 85 percent of all consumptive water use – mainly from the Ogallala aquifer. With unsure rainfalls and aquifers diminishing faster than they can recharge, the trick is knowing exactly how much stress a crop can take, and precisely adjusting irrigation to still result in a profitable harvest. Dr. Isaya Kisekka, an assistant professor in K-State’s Department of Biological and Agricultural Engineering, is working to take the guesswork out of the equation and give farmers the tools they need to maintain their net profitability and protect the state’s water resources for future Kansas farmers.
At K-State’s Southwest Research and Extension Center Finnup farm near Garden City, Dr. Kisekka and his team planted approximately 30 acres of corn to examine exactly what tools and techniques would give farmers the best yields with less water. Dr. Kisekka is an expert in this field, having studied irrigation and its effects since his days as an undergraduate student in his home country of Uganda. For this experiment, he divided the land into equal plots, and randomly assigned five different irrigation schedules to each. The sixth treatment was full irrigation. By the end of the study, he and his team would know which tools would best help farmers to achieve yields substantially equal to those found on fields receiving full irrigation.
But they would do it with 20 percent less water.
The team checked their crop in a variety of ways. Some plots were checked weekly with a moisture meter called a neutron probe, and those plots received their irrigation only when the probe showed that the soil water had dropped below a certain percent. Similar plots had soil water sensors permanently buried beneath the growing plants. These sensors measured the available soil water near the root zone, and alerted the team when the plants needed water. Other plots had thermal infrared radiometers – they look like a small camera mounted atop a pole that extends above the crop – to provide a high-accuracy temperature reading of the crop canopy. The team irrigated these plots once the temperatures exceeded a specific limit. The remaining plots used a combination of data from the radiometers and soil water sensors.
Because of this study, farmers with constrained water supplies can improve both water and crop productivity: by monitoring the soil or plant water status, along with more traditional methods of calculating a crop’s water balance called ET-based scheduling, irrigation water applications are optimized. Adopting scheduling based on calibrated soil water sensors and canopy temperature sensors, along with measuring the crop’s ET-based water balance could help maintain yields while eliminating unnecessary irrigation applications.
Dr. Kisekka and his team hope that this study will encourage farmers to try deficit irrigation: they can combine their traditional irrigation systems that are based on evapotranspiration with soil water sensors and plant water status monitoring systems. The next phase of this project will include on-farm research to supplement the controlled findings from the Southwest Research and Extension Center farm. Dr. Kisekka and his team will also begin exploring other advanced irrigation scheduling techniques using plant diameter sensors and model-driven decision support tools.
Hopefully, these studies will provide farmers with the needed technology to navigate the changing future of agriculture: how to grow more crops with less water.