I don't know much about manure ponds. Are you draining it for a reason and are you planning to keep using it as a manure pond? Do you just drain it on the farm land or spray it?
The farm that I'm buying was a dairy farm; and I may dairy on it again, I'll be working on that question in the next year; it was a licensed grade-A dairy, which is the highest license standard. As part of that licensing there are a variety of inspections that are required, tests and plans. A manure lagoon is very expensive and time consuming to permit as new; this one exists and is already permitted and approved. To permit and construct a new lagoon in western washington will cost between $325k and $400k.
Dairy cows eat quite a bit, and generate a lot of manure; this farm had 300 cows being milked, and each cow was eating at least 40lbs of dry matter per day along with all the water that they could drink. On just a dry matter basis (300 * 40 /2000 = ) 6 tons of manure a day. But when you add water to that it's probably a lot heavier.
|Cows are kept in a limited area and feed is brought to them|
In this area, that's the legal, and required, way to manage the manure from a dairy. Even if the cows are kept on pasture during part or most of the year, there's a part of the year that they are kept off the fields to keep the grass in good condition for next year.
Dairies are required by law to not discharge any water or waste off their property, and are limited in the amount of manure that can be spread on fields. The state comes out and tests their fields to make sure that an appropriate amount of manure is being spread, so that runoff doesn't occur.
So to answer the question directly: In the spring, manure lagoons are stirred up and pumped out to provide fertilizer for the fields. In my case, about 1.5 million gallons got pumped out. In the fall, the manure lagoon is pumped out again and spread, usually accompanied by the planting of some fall cover crop.
The fall pump out is to empty the lagoon so that you have enough capacity to hold all of the waste generated during the winter, when you have the cows in the barn eating hay and saving your pastures for spring.
To get as much of the manure into the ground as possible, the ground was prepared with a disc, and then the tractor doing the pumping also scored lines in the ground to help the liquid soak in. We've also had three days of hot sun, so at this point the ground is damp but that's about it. Corn will be planted in the next day or two.
Whatever I do, I will be generating a lot less manure than the 300 cows that used to be here.
Note: The manure lagoon is just a way of dealing with large amounts of waste. Every cattle farmer who keeps their cows in a barn for the winter will also deal with quantities of manure, spreading it on the field and so on. Dairy farmers tend to be visibly doing this because they usually deal with very large amounts of manure and they are very heavily regulated, but every cattle farmer has the same basic issue, especially over the winter.
Boarding stables and horse owners in this area have the same problem. Most of them handle their waste by trucking it somewhere else. Personally, I prefer to keep my waste on my own farm and get as much use out of it as possible.