Overfeeding macro minerals can lead to excessive concentrations in soils
By Carol Ryan Dumas
TWIN FALLS, IDAHO — Researchers at the University of Idaho are continuing their work on creating “designer manures” by adjusting cows’ nutrient intake to alter the excreted manure, which ends up on cropland and affects crop production.
Their most recent research is focused on the macro minerals sodium, potassium, magnesium, and calcium, which cattle require in relatively large, daily amounts.
Land application of macro minerals in dairy manure isn’t currently under regulatory control or in dairymen’s nutrient management plans, but over application can lead to excessive concentrations in soils, according to the UI researchers.
The research is trying to address concerns about a buildup of macro minerals – particularly salts – on farms, said Rick Norell, UI extension dairy specialist, during the 2014 Idaho Nutrient Management conference in Twin Falls last week.
Dairy nutritionists formulate diets to meet cows’ requirements with some overhead to allow for differences in feed composition and ensure adequate intake for optimal health and production. In addition, exact formulations are not economical, and specific nutrients are added to serve a specific function, such as addressing milk production cycles and heat stress, he said.
But excess intake of those minerals increase mineral excretions in manure that is going to be land applied to grow crops. Excess sodium and potassium, both salts, primarily flow into the urine stream, while excess calcium and magnesium increase excretions of those minerals in feces, he said.
Feeding excess sodium and potassium can lead to an excessive salt load in soils. Those salt loads can cause toxicity in plants, induce water stress, seal soil surfaces, and lower crop yield, he said.
Sodium, in the form of salt or sodium bicarbonate (used as a rumen buffer), in commercial feed additives and mineral supplements have a lab analysis, so producers know the mineral content. But producers should avoid free-choice offerings of the minerals. And if they are offering free-choice salt, it should be in block form rather than granular, as cattle will eat twice as much in granular form, he said.
Forages should be analyzed, as they are highly variable in mineral content and provide 50 percent to 75 percent of the dietary intake of sodium and potassium, as well as calcium, he said.
Dairies that manage manure by scraping have more sodium and potassium in solid manure, while dairies that manage by flushing have more in the primary storage lagoon, he said.
Minerals in water can also be an issue, as cows drink an average of 40 to 45 gallons a day in hot weather. There typically isn’t much to worry about as far as water being a mineral source, but in a worse case scenario of very hard water, it could be an issue, he said.
Norell and fellow researcher Mireille Chahine recommend producers identify which feeds should be tested, based on the variability of the nutrient content of the feed and how much of the dietary nutrients are provided by the feed. They also recommend analyzing feeds using wet chemistry, creating a historical library of results and analyzing water supplies.