After the Soil Sample
Agronomist offers tips for using manure or compost on fields.
“For some reason, the world outside of agriculture thinks that the farmer just goes out and puts on a pesticide whenever he wants,” called out Cameron Brower, a certified crop advisor for Stukenholtz Laboratory Inc., at the 2017 Idaho Farm Bureau Young Farmers and Ranchers Leadership Conference in January 2017.
“We know that’s completely wrong! They don’t realize that you’re running a business, and there’s a cost to everything, so we’ve got to do a better job of teaching the world what you really do and that you are good stewards of the land,” he continued.
Brower defined a good land steward as someone who understands issues concerning sustainability, labor and social outlook, and, of course, economics. A good steward is responsible with resources — both natural and financial. When growing crops to feed and clothe the world, a good steward needs to know exactly where and how to allocate those resources. This process starts, he said, with a soil sample.
A soil analysis will tell us the existing soil nutrients, said Brower. We can use that information to responsibly fertilize the soil and crop, without leaching nutrients into the aquifer and causing environmental problems.
Plants require 16 essential nutrients to grow. Three of these come from the atmosphere: carbon, hydrogen and oxygen. Primary nutrients include nitrogen (N), phosphorus (P) and potassium (K). Secondary nutrients are sulfur, calcium, magnesium and chloride. Zinc, iron, copper, manganese, boron and molybdenum are all micronutrients.
While a certain amount of each nutrient is needed for plant growth, the most important nutrient is the one that is the most lacking or limiting.
Manure or compost
Manure is definitely not a lacking resource for most cattle producers. In fact, when used appropriately, it becomes a valuable resource.
Brower encouraged his audience to use manure or compost, if they have it available.
“In most cases, in most years, we see great value in manure or compost applications. We see a good return on investment,” he stated.
Brower defined manure as the raw output from cattle, ranging up to 80% water and fairly high in N.
A good rule of thumb for nutrient availability in manure in the first year is 5 pounds (lb.) N, 3 lb. P and 7 lb. K. However, the best way and truly only way to know for sure is to pull a sample and have it tested, Brower clarifies.
Compost, he said, is decomposed and dried manure. It has less N than manure because it volatizes and gasses off during the composting process.
“You get a little bit of N lost from compost, but it does have a better concentration of P and K; less weed seed because those weed seeds get annihilated through that composting process.”
While nearly all manure is somewhat composted, actual compost composition varies. Different animal types: beef or dairy, diets, water content, amount of bedding and exposure time — how long it’s been exposed to the elements — contribute to compost’s complexity.
Compost quality also varies within the compost pile, said Brower.
He added, “We can pull samples off of compost piles, and you’ll find that on top of the pile it’s dry, but you try to push in as deep as you can, and the deeper you go, you find more moisture.”
As logic would assume, compost can vary significantly from pile to pile. Brower uses Snake River Farms, a local feedlot in Brower’s area that sells compost to farmers, as an example.
“We see so much variance that we have to make sure that when we pull a sample of that compost pile that that is the compost pile that is going to the field we’re expecting it to go to. Otherwise it can vary and can throw us off,” he said.
Average compost in its first year at a rate of 1 ton per acre, said Brower, would feed the soil with 2 lb. N, 10 lb. P and 35 lb. K.
Brower believes manure or compost is worth spreading due to its valuable nutrients, but he warned about too heavy of an application. The mantra, “If a little is good, more is better” does not apply to manure, compost or fertilizer, he said, referring to environmental concerns and overall soil fertility.
Both manure and compost are high in salts, he explained. The problem with salty soil is that water is less attracted to the root of the plant, making it difficult for the root to absorb.
“A high-salt crop actually looks like it’s drought-stressed because it just can’t take in water,” he described.
For cattle producers, manure and compost are available fertilizer resources to consider when planning crop management strategies. However, accurate, responsible and economical application of animal waste can only be achieved by starting with a soil sample.
Editor’s Note: Paige Nelson is a freelance writer and cattlewoman from Rigby, Idaho.