Weigh risks of applying manure

By Gary Sliworsky
Ag rep, Emo

A potentially early grain harvest may make some producers decide that this is the year to apply manure or compost.
Before heading to the field, however, take a few minutes to take a sample of the material and think about the composition of the material being applied.
What are the benefits? Are there risks? How can those risks be minimized?
Benefits include:
•organic matter and nutrient benefit for the soil;
•reduced commercial fertilizer inputs;
•feeding of soil bugs that help to improve soil health;
•little risk of compaction;
•more time available (compared to spring or fall) to apply to fields further away from the storage; and
•opportunity to seed a cover crop to maximize soil health benefits.
There always are a few risks. Summer is the best time to apply solid manure, especially manures that include bedding.
Summer/fall weather conditions help soil organisms to mineralize the organic nitrogen the makes up the greater portion of solid manure, so that the nutrients are more available for the crop the following spring.
The risks associated with solid manure or compost are lower than with liquids applied at this time of year.
During a sudden thunderstorm, liquid manure has a higher risk of run-off and for entering tile drains, especially in no-till cropping systems.
Manure in tile drains can end up in rivers or streams, where the ammonia will kill fish.
Run-off containing phosphorus also is harmful in water sources.
Pre-tillage or injection, so that earthworm and root channels are disturbed, will increase infiltration of liquids and nutrients, reduce odours, and can mix in seeded cover crop seed.
Liquid manure has higher ammonium-N content. If liquids are surface applied to dry soils during the hot, hazy days of July and August, 75 percent of the ammonium portion could volatilize into the air.
Odour complaints near residential areas would be likely.
Incorporation will help, but liquid manures are best applied later in the season when soil and air temperatures are closer to 10 degrees Celsius.
Liquid manure has a higher ammonium-N content that converts quickly to nitrate-N under summer conditions.
Nitrate-N can move with water. In a wet fall, if there is no growing crop to take the nitrate-N, it will move below the root zone and potentially to tile drains or ground water.
Either way, that nitrogen is not available for the crop the following year.
Where liquids are being summer applied, the addition of cover crops will help to prevent nitrate-N from moving below the root zone and help to hold the nutrients in “green” form.
In some cases, such as oat cover crops, growth can be sufficient enough for a forage harvest.
As manure is applied to those early-harvested grain fields, remember to take manure and soil samples, account for the additional nutrients applied when planning commercial fertilizer additions, and pay attention to the weather forecast.