PICTURE BUTTE, Alta. – Field manure application has received a bad rap in recent years because of odour and pollution complaints, but it remains a valuable building block for soil when properly used.
“We really want to look at manure as an extremely valuable resource,” said Ross McKenzie, an Alberta Agriculture agronomy researcher.
However, agronomic and environmental problems may result if it is not handled properly, he told a nutrient management seminar in Picture Butte.
Manure, which contains nitrogen, phosphorus, potassium, sulfur and micronutrients, can rebuild the soil’s ability to hold water, add organic matter, reduce surface crusting and improve water permeability.
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“If we overapply nutrients, the yield and quality of the crops we are growing will decline,” he said.
Overloading manure on the same field year after year results in too many nutrients that can damage a crop and leach serious disease-causing agents and other pollutants into the water supply.
Excess nitrogen may result in reduced yields and more lodging of crops such as wheat and barley, especially for those grown with irrigation. There is also a risk of increased salt levels from hog manure that further reduce yields.
Uneven application also affects uniform crop growth.
McKenzie advocates testing soil and analyzing manure for available nutrients to make sure each crop receives what it needs.
He recommended testing the soil at varying depths of six, 12 and 24 inches every year to analyze whether nutrients are deficient, low, medium, sufficient, high or excessive. Farmers should also sample to a depth of 48 inches every five years to assess what chemicals have moved downward. Look for nitrogen, phosphorus, potassium and sulfur levels as well as pH and soil conductivity.
It is also good to know how much of each nutrient is taken up by the plants and how much is lost in runoff, leaching, nitrification and volatilization, which is when nitrogen gas is lost to the atmosphere.
“It is virtually impossible to apply manure to match the exact crop requirements,” McKenzie said.
If adequate nitrogen is applied, potassium and phosphorous levels would then be four to five times more than the crop needs.
“If you do that every year, you are going to run into trouble,” he said.
Some of the nutrients in manure are in the organic form, which makes them unavailable to plants in the first year of application.
For example, beef cattle manure contains 17 to 21 pounds of nitrogen per tonne, but only four to five lb. are available to plants in the first year of application. Hog manure has seven lb. of nitrogen with 3.2 lb. available. Poultry manure has 19 lb. of nitrogen and 15 lb. are available.
Half the nitrogen in feedlot manure is found in the solid form and the rest is in urine in the form of ammonia. The nitrogen converts to nitrates, which crops can take up easily but which can also leach.
A considerable amount of nitrogen can be lost into the air as ammonia if manure containing lots of urea is broadcast. This is known as volatilization.
Warm, windy weather increases nitrogen loss if it is not incorporated quickly into the soil. Less is lost into the atmosphere if applied when temperatures are cool in the early spring or fall.
Feedlot manure applied at a rate of 10 tonnes per acre will deposit 200 lb. of nitrogen, 180 lb. of phosphorus and 260 lb. of potassium. A barley crop that yielded 120 bushels per acre would remove 140 lb. of nitrogen, 45 lb. of phosphorus and 35 lb. of potassium.
“The majority of nitrogen is going to be taken up but the majority of the phosphorus is going to be left behind,” McKenzie said.
From the 1970s to 1990s, farmers were told to apply manure based on the plant’s nitrogen requirements, according to Alberta Agriculture’s code of practice calculations. That has resulted in a buildup of soil phosphorus in regions where plenty of manure is available.
“Once you start having problems with higher phosphorus levels, then we need to look at how we change our manure management,” he said.
Phosphorus levels are considered to be very low if 20 lb. per acre are found in the top six inches of soil. Low levels are 20 to 35 lb., medium is 35 to 50, medium to sufficient is 60 to 90, high is 90 to 120 and excessive is more than 120 lb. per acre.
Crops respond well when there are 60 to 90 lb. of phosphorus per acre. Yields do not improve when phosphorus is higher than 90 lb.
“I see no reason to put on manure or commercial fertilizer once you are above that level,” McKenzie said.
Half of the available phosphorus will release in the first year of application, which means plants take up 90 percent of the nutrient in three years.
