Manure nutrient availability is not always like fertilizer
Not all nutrients are created equal when it comes to manure. Some are bound to organic particles and will release slowly over the first and even the second growing seasons after application. Other nutrients are plant-available right away and behave similarly to commercial fertilizers after application. More specifically, nitrogen (N) availability of manure varies by livestock species and how the manure is applied. See the table below to get an idea of what percentage of the total N measured in the manure you can expect to be available for next year’s crop. This table assumes that you are applying the manure in the fall when soil temperatures are less than 50°F.
Table. Manure nitrogen availability as affected by method of application and animal species (% N available per year)
| Species & year | Broadcast + incorporate >96 hours | Broadcast + incorporate 12-96 hours | Broadcast + incorporate 0-12 hours* | Injection with sweeps | Injection with knife or coulter |
|---|
| Beef year 1 | 25% | 45% | 60% | 60% | 50% |
| Beef year 2 | 25% | 25% | 25% | 25% | 25% |
| Dairy year 1 | 20% | 40% | 55% | 55% | 50% |
| Dairy year 2 | 25% | 25% | 25% | 25% | 25% |
| Swine year 1 | 35% | 55% | 75% | 80% | 70% |
| Swine year 2 | 15% | 15% | 15% | 15% | 15% |
| Poultry year 1 | 45% | 55% | 70% | n/a | n/a |
| Poultry year 2 | 25% | 25% | 25% | n/a | n/a |
*including double disks
For the other nutrients, we expect that 80% of the total phosphorus (P) and 90% of the total potassium (K) measured in the manure via a laboratory test will be available to the crop the following growing season. Less is known about sulfur availability at this time, but we estimate roughly 50% of total sulfur in the manure is available.
Spread it out
Since manure is a complete nutrient source, you can choose several different application rates based on your goals for the field. Typically, the N-based application rate (to supply full N needs of the following crop) is the highest you can apply in a field. This usually results in more P and K than is needed for that crop. If you are trying to get the best bang for your buck, consider applying the manure at a lower, P-based rate, and then supplement the rest of the N needs for the crop with commercial fertilizer. That way the nutrients are balanced for crop needs, and you can spread manure on more fields! Remember that manure also has carbon, which can help improve the organic matter content of your soils. Spreading the wealth to as many fields as possible can be beneficial in the long run.
Watch your nitrogen
In Minnesota, regulations state you cannot apply more N than the crop needs in any given year. This means you’ll have to account for first-year availability of N in the manure plus any other fertilizers applied to the field that might contain N (like starter fertilizer, MAP, and DAP). In the second year after manure is applied, you have to take a second year N credit for the manure.
Put a value on it
One of the questions we’ve been getting recently is how to put a dollar value on manure. This depends on several factors, like whether your field needs P and K, what kind of equipment you’ll be using to apply the manure, etc. Luckily, we have a web-based calculator to help you out! You’ll want to make sure to plug in current fertilizer prices (which seem to be changing rapidly these days!) as well as your specific information. The great thing about the calculator is that you can play around with the numbers to see where you can get the best value from the manure.
Source : umn.edu