The increased salinity of the South Platte River represents a potential catastrophe to irrigated farming in the valley, but there are alternatives. And, like all solutions to potential disaster, they’re costly and they will require some re-thinking on farming methods.
Information on the growing salinity of the river was presented Wednesday at a workshop organized by the Centennial, Morgan and Sedgwick County Conservation Districts. The workshop information included some from a study commissioned by Colorado Corn Growers Association and Colorado Corn Administrative Council, and due to be released later this month.
According to Mike Petersen, a retired soil scientist and agronomist who presented at the workshop, the situation in the South Platte Valley isn’t dire yet but unless changes are made, the situation will only become worse.
The first change is to stop plowing the ground every year, and leave residues on the surface as long as possible. Plowing, Petersen said, releases needed soil moisture into the air, which leaves salts behind, this concentrating them.
“To put it bluntly, just stop plowing,” Petersen said. “I’m a big fan of no-till farming.”
One step is to use non-ionic surfactants in irrigation water. Farmers add surfactants to make the water “wetter,” so it soaks into the ground and gets to the plant root zone. It’s similar to the way a detergent acts in dishwater or a clothes washer. Many surfactants are “anionic” which means they have a slight electrical charge that binds them to minerals in the soil. Non-ionic surfactants are biodegradable and plant-derived from sugars, usually glucose derivatives, and fatty alcohols. Once they do their job, they break down in the soil and become inert.
Better water management is another key to controlling salinity. According to a 1989 treatise on soil salinity by the Food and Agriculture Organization of the United Nations, flood irrigation and furrow irrigation are best for salinity control, but may need to be combined with sprinkling. Petersen recommended irrigating between 2 a.m. and 4 a.m. as that’s when the plants take up water most efficiently.
Biostimulants that encourage microbial growth in the soil will help plants overcome the potassium-blocking effect of salts in the soil. Potassium is a “big sister” to nitrogen, in that it grabs nitrogen by the hand and pulls it up through the plant system.
The 2018 Farm Bill defines a biostimulant as “(A) substance or micro-organism that, when applied to seeds, plants, or the rhizosphere, stimulates natural processes to enhance or benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress, or crop quality and yield.”
It’s the first time federal legislation has ever defined biostimulants, and the USDA hopes it will lead to more widespread use of them.
Petersen also recommended not using, or at least using much less, sulfur-based soil amendments. Gardeners are familiar with sulfur-based fertilizers with brand names like Miracle Gro and Azomite. Sulfur is beneficial to plant growth, but Petersen said over-use of it can worsen salt content in soils.
Cash crops and cover crops that are “salt tolerant” can, over time, actually remediate salty soil. According to Successful Farming Magazine, cash crops that do well in salty soil are barley, camelina, rye, safflower, sunflower, and sugar beets. Cover crops that can help remediate the soil include barley, rye, Siberian millet and sorghum-Sudan grass.
Petersen strongly recommended rotating crops to minimize salinity as well.
“Corn on corn on corn on corn is just asking for trouble,” he said.
The USDA and Colorado State University have several recommendations for good crop rotations in eastern Colorado, depending on location and whether the crop is irrigated or dryland.
None of the measures to counter soil and water salinity are exactly cheap, and in some cases growers may have to make some hard choices. Still, he said, it beats the alternative of doing nothing.
“It ain’t ever going to be like the good old days,” he said. “Change is mandatory.”
