After sitting through a webinar yesterday about new things happening in the world of agriculture, I decided that today would be a good day to take a look at manure. Manure is one of those things that can either be used effectively and can be beneficial for the environment OR by abusing it’s use it can create water contamination and have detrimental effects on the environment.
What is manure?
Manure is well…poop from animals.
It contains undigested pieces of corn and other grains , bits and pieces of undigested hay and the waste from digested foods. Manure from animals really isn’t that different from human feces, other than the animals diet is much less complex and doesn’t vary in what foods are eaten. They eat the same basic ingredients for 2 or 3 meals a day, 7 days a week, 365 days a year. Hays from grasses, silage from corn and grains.
Poultry poop is a little different. It can be dropped in spots between the size of a dime up to the diameter of about a quarter (25 cents). It is high in nitrogen but doesn’t contain bits of what they eat. The color of the manure may change if they are allowed to roam a pasture to a darker green in color but if they are housed inside and feed a grain diet the manure will be a lighter green to almost brown color. And of course, lets not forget that little white spot on top. I am still not sure why they do that!
The principal value of manure is its extended availability of nitrogen within the soil.
Now, that you have manure: What do you do with it? How is it used?
What the farm does with it really depends on the size of the farm and what type of animals are there.
Small farms like us will usually clean the barns daily and pile the manure into a compost pile. That pile is turned with the bucket on the front of the tractor. Our compost piles also contain bedding materials like wheat straw, poultry manure and wood shaving from the barn floor and nest boxes.
Farmers who have more animals than I do, typically have a manure spreader and will spread the manure upon fields that will be planted into crops or used for hay. How often they spread the manure depends on the size of the farm. The other farm I work on has a 76 head barn that the manure gets spread twice per day. I know of another one with about 25 head that spreads every two days. Farms of this size are currently allowed daily spreading of manure, even during the winter months.
Larger farms with more than 200 head of cows need to have a manure management plan in effect. You can think of this as a map with written direction on field locations and when the fields will be spread. The plan also includes, on larger farms, manure storage and transportation. Most of the larger farms also have a manure storage of some sort. Some of the older farms have in-ground pits that look much like a small ponds while others have recently incorporate the use of concrete “pools”. The manure is then pumped out of the unit and spread, as needed on fields as a fertilizer.
A few of the larger farms, which I am going to estimate the head count at 1,000 plus, have added ponds or pits with a covering. That covering allows for the materials to compost down, much like I do on my farm but it has an enclosure over the top of the area. That enclosure will usually have a capture unit on the top that will transport the gases released form the composting process (methane) to a storage unit or a unit that generates electricity. After the material has decomposed it will become a liquid, without the smell of traditional manure, that is then applied as a fertilizer to the field.
How is manure a fertilizer?
Manure is an excellent fertilizer containing nitrogen, phosphorus, potassium and other nutrients that are needed for plant growth. Nutrient content and the rate nitrogen becomes available for plant use depends upon the source, moisture content, storage and handling. Manure also adds organic matter to the soil which may improve soil structure, aeration, soil moisture-holding capacity and water infiltration.
To determine how much manure is needed the nutrient content and the nitrogen rate needs to be estimated. Moisture content is a major consideration. For example: Moisture content of fresh manure is around 75-80%; air-dried is around 9-15%. As manure dries, the nutrients concentrate on a weight basis but also on a volume basis. Urine nitrogen can evaporate into the air at a rate up 50% or more.
Knowing the basic information on manure is important so you know what to spread on which locations based off the nutriental requirements of the crops and what nutrients are held within the soil. The soil values are determined by doing soil sample tests at different locations within a field.
Available nitrogen from complete organic compounds, such as bedding materials, is released gradually. You can think of this like a slow release pain medication you would take. The slow release of nitrogen is the manure’s most important asset as it extends the nitrogen available within the soil and reduces leaching problems.
The basic guidelines are to apply enough manure to meet the first year need for available nitrogen. After that, you decrease the amounts applied the following years due to carry-over nitrogen released from previous applications. If applying manure from poultry, the nitrogen release at a rate of approximately 90% the first year. Fresh manure that contains both urine and solids with a high amount of urea releases approximately 75% of the total nitrogen in year one. Solid manures release much slower with a rate of approximately 35% of the total nitrogen released during the first year.
Improper Use and Disadvantages to Using Manure as Fertilizer:
If the same rates of manure are applied every year, a field that may have originally been low in nitrogen can become unnecessarily high over the following years. This can cause contamination of water supplies (I will discuss this more on Monday’s blog) and create additional issues throughout the whole farm. Excess nutrients, whether in the form of manure or synthetic fertilizer, can run off or leach into the environment and contaminate streams, lakes, and wells.
Weed seeds are also common in manures. Fewer are found in Poultry manure due to the effective digestion of the animals. Seeds in manures can come through feed, litter or just blown into an area (think dandelion seeds). The seeds can pass through the digestive tract still viable. High rates of weed seeds within manure could result in the potential use of Round-up to kill the weed growth. Composted or stockpiled manure will reduce the number of viable seeds within the manure.
Manure also contains 4-5% soluble salts on a dry weight basis but can run as high as 10%. An application of manure containing 5% salt of 5 tons adds approximately 500 lbs of salt to the soil. Irrigation and rain water will assist with the leach process in well-drained soils, preventing salt accumulations. Salts in poorly drained soils, soils with salinity issues and/or high application rates need to pay close attention around new growth plants.
Too much manure application can cause P (phosphorus) and K (potassium) to accumulate in soils with a history of manure applications, and may eventually reach excessive levels. Excess levels of soil P can increase the amount of P in runoff, increasing the risk of surface water degradation. Many crops can handle high levels of K, but livestock can be harmed by nutrient imbalances if they consume a diet of forages with high K level.
I don’t claim to be an expert by any means on the actual values within manures. This is why soil sampling is very important. Soil sampling and advice from a soil adviser ensure that you are applying the proper balance of nutrients to the soil.