I'll bet you didn't know that some people make a study of manure. We have over a half million dairy cows within 75 miles of here, and cheese and yogurt factories to process the milk. As you can guess, the amount of manure produced is very large and it very hard to dispose of. We have a number of compost operations around the area but most is spread on the land. However, there's only so much you can spread on the land without destroying the soil.
Here's an interesting article on how researchers are trying to 'custom design' manure by manipulating the feed that goes into it.
Designing a Better Manure
TWIN FALLS � �What goes in, must come out� applies to dairies as well as thermodynamics.
Researchers are beginning to put that principle to work to help create �designer� manures to prevent build up of macronutrients in the soil, but feed costs will limit how widely the practice is adopted.
Most nutrient plans written for Idaho dairies are primarily concerned with nitrogen and phosphorus levels, but other macronutrients can also be a concern. Calcium, magnesium, potassium and sodium are all macronutrients whose levels in manure and urine can be influenced by feeding practices.
Cows need calcium for many of the same reasons humans do, but feeding cows more calcium doesn�t make the milk they produce more calcium-rich. Instead, the amount of calcium in the feces increases. That�s also true when magnesium levels are increased in rations.
Increasing potassium and sodium levels, which are both salts, increases the concentration found in urine but also does not impact milk content, explained Rick Norell, University of Idaho extension dairy specialist in eastern Idaho, during the UI nutrient management conference held last week.
A study of 39 large dairies in California found that all of them were feeding calcium, magnesium, potassium and sodium at levels above National Research Council (NRC) recommendations.
That�s partly because the NRC recommendations were published more than two decades ago and cows are more productive today and require more nutrients.
But it�s also because dairy rations are not exact formulations, Norell said. Nutritionists formulate rations to meet the energy requirements of lactating cows, but aren�t as concerned about about minerals such as calcium.
However, dairies are becoming more concerned about buildup of macronutrients � particularly salts � in soil where manure is often applied. To track macronutrient levels, Norell recommends testing loads from major suppliers and those feedstuffs that have the greatest variability in macronutrient content.
He wouldn�t bother to test salt or bicarbonate fed to dairy cows but those products come with a guaranteed lab analysis. Forages, on the other hand, vary dramatically in terms of macronutrient content.
If salt buildup is a concern, dairies should avoid feeding free-choice mineral and instead force-feed salt to give cows what they need. If a dairy does decide to offer free-choice salt, provide a block rather than granular salt. Studies have shown that cows eat twice as much granular salt as they do salt from a block.
While ration formulation can impact how much manure or urine is produced and what the macronutrient content of that manure is, how dairies handle the manure is also important.
Soluble salt concentrations, for example, are much higher in solid manure from dairies that scrape manure. But concentrations are highest in the primary lagoon on flush dairies.
Because lagoon water cannot be transported as far from the dairy as solid manure can be, the potential for increasing salt levels in fields where lagoon water is applied is greater. Corn can tolerate higher salt levels, but beans and potatoes are more sensitive.
Howard Neibling, UI extension water management engineer, believes dairies should be more concerned about salt levels in urine and manure. The only way to reduce high salt levels in fields is to leach the salts through the root zone, which also moves other nutrients.
Dairies are concerned about salt levels in soil, Norell said, but they are more concerned about managing feed costs.
�They are not going to balance rations for macronutrients now,� he said. �The chance to make an improvement is driven by the need to make an improvement.�
