The Back End: September-October 2015
By Dan Andersen
Small dairy manure mgmt: Is storage right for you?
By Dan Andersen
Growing up on a small dairy, manure was a part of daily life. Rain, shine, snow and cold, or heat and humidity, one thing remained the same, after finishing morning milking it was time to run the barn cleaner and haul a load of manure.
This wasn’t something unique to our farm, most of the dairies around us were doing the same thing. Hauling manure was a just a part of daily life. As bigger farms moved in, they started building manure storages and land applying their manure in the spring and in the fall, working around their other cropping schedules.
From a management perspective, the use of storages makes perfect sense as it alleviated the need to go out in the snow and rain and apply manure. Applying manure during rain, or when soils are frozen or saturated, can cause compaction and lead to offsite runoff of our manure nutrients, things we want to avoid. By storing the manure, we can focus our application periods in times just prior to planting or after harvest in the fall (once our soils have cooled), which allows the use of injection or immediate incorporation application techniques, both of which get the manure in contact with the soil and helps protect the nutrients from transport and loss. This helps keep near-by streams, rivers, and lakes clean and those nutrients in the root zone, where they can feed our crops. However, despite these potential positive benefits we still see many small dairy farms without manure storages. This got me wondering: would the improved nutrient use that having a manure storage could provide pay for the cost of constructing the storage on these smaller dairy farms?
To find out, I looked at an example case of a 100-head dairy. According to the American Society of Agricultural and Biological Engineers (ASABE) standard, each cow will make about 18 gallons of manure a day. Assuming we are going to have six months of storage, around 350,000 gallons of storage capacity would be required. Figuring about $150 per 1,000 gallons to build the storage, we’d have to spend a little more than $50,000 on construction. How does this compare to the nutrient value it will help us capture? With either a storage or in the daily-haul system, we can capture most of the value from phosphorus and potassium as these nutrients will bind to the soil particles well enough that most of what we apply will still be there for our growing crop. However, the big difference will be in nitrogen (N). If we are out there applying manure all winter, we effectively will be capturing almost none of the N in the manure. However, if we store it, inject or incorporate as we apply, we can do a lot better. Looking at my manure production number I’d estimate that each cow excretes about a pound of N per day. In the daily haul system we probably are capturing and using somewhere around 1/3 to 1/2 of this N (though it can vary greatly depending on your soil conditions, the crops you are growing, how you are applying, and the characteristics of your manure). In a manure system with storage, we can do better, and I’d guess are probably capturing close to 70 percent of the N. This means that by building a storage, we’d be capturing an extra 7,000 to 13,500 lbs. of N per year, which has a fertilizer value of about $4,000 to 6,750. This means that even on a farm this size the manure storage would help pay for itself within 15 years.
Construction of manure storages can certainly be expensive, but they can facilitate better use of manure nutrients on your farm and can quickly pay for themselves. Manure storage may allow you to better time your manure nutrient applications to meet your crop needs and keep the nutrients in our field until you need them, making your operation more sustainable, more cost competitive, and a better environmental steward. And best of all, you can take that extra half-hour a day you were spreading manure, and spend that time focusing on what matters most – the cows.
Dan Andersen is an assistant professor in Agricultural and Biosystems Engineering at Iowa State University. You can find him on Twitter (@DrManure) or check out his blog at themanurescoop.blogspot.com.