Excessive nitrogen in pig manure
Farmers who apply liquid pig manure to their fields can seriously pollute soil and water if the slurry contains more nitrogen than the plants can handle. This problem can be reduced by closely monitoring what the pigs are fed.
There is an ideal balance which meets the needs of the pig without supplying excessive nitrogen. Dietary protein supplies the amino acids in varying amounts. Some amino acids are more than the pig needs. These unnecessary acids are broken down and excreted as urinary nitrogen.
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However, by properly using synthetic amino acids, it is possible to reduce crude protein levels without reducing pig performance. This reduces the amount of nitrogen broken down and excreted by 25 percent or more.
The resulting slurry can be applied at higher rates per acre, an important consideration where time or land base is a constraint. Also, as slurry nitrogen is reduced, so is the atmospheric nitrogen. Any opportunity to reduce odor needs to be seized.
Another aspect to reducing nitrogen output is to examine digestibility of the individual ration ingredients. Not all dietary protein is equal. The presence of high fibre, antinutritive substances or large imbalances in the amino acids profile contribute to poor digestibility, poor availability and subsequent high excretion rates.
Higher nitrogen in the manure slurry requires a larger land base for spreading.
A 1997 survey of slurry nutrient levels in Manitoba showed that average total nitrogen was 27 pounds per 1,000 gallons, phosphate was 19 lbs., potash 16 lbs, and sulphur two lbs.
But the range was wide, illustrating the need to analyze the slurry before it is spread. The highest nitrogen level was 68 lbs. per l,000 gal. while the lowest was seven lbs. Phosphate ranged from one to 118 lbs. and potash from four to 38 lbs. Sulphur showed the smallest variation, ranging from zero to five lbs. Without proper testing, too many nutrients could be applied.
Using the average nitrogen survey results, assume soil test levels of 40 lbs. of nitrogen on the target field. The objective is to have a total of 100 lbs. of nitrogen per acre for a cereal crop where moisture is adequate. Slurry nitrogen per acre needs to be 70 lbs. per acre. At 28 lbs. of nitrogen per 1,000 gal. of slurry, it’s necessary to apply 2,500 gal. of slurry per acre.
For one million litres of slurry, a spread field of 89 acres is needed. Any change in soil test levels, slurry levels or crop nutrient needs will change the acreage needed to spread the slurry.
– Manitoba Agriculture
