David Schmidt
Assistant Extension Engineer
Many dairy producers in Minnesota are considering step-wise herd expansions. In the initial stages the herd is often increased from 30 or 40 cows to 100 or 150 cows. In many cases, construction of a long-term manure storage (6 to 12 months) can not be afforded during the initial transition step. That is, the long term storage unit would be constructed once the dairy herd is expanded to its ultimate size (perhaps 150 to 400 cows). However, during the transition phase some sort of short-term manure storage is needed to facilitate the handling of manure scraped from the freestall barn. Manure must be removed from the alleys at least twice each day to keep cows clean. If a structure is not provided to contain the slurry the manure would need to be hauled to the fields twice each day. Most producers do not have time to haul manure twice each day, and field conditions may not be suitable for spreading. As a result, cow cleanliness suffers if some sort of manure containment is not provided. A ramped, concrete mini-pit (shown in Figure 1) can provide a low-cost, short-term storage that will improve labor efficiency, and allow better management of the freestall area. A mini-pit is also a short-term storage alternative that works well with sand- bedded freestalls.
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A mini-pit should be located off the east end of a 2 or 3-row freestall barn or south of the cross alley of a drive-through barn to avoid prevailing winter winds. Manure is scraped from the building into the pit with a skid-steer loader. When selecting the location of the mini-pit be sure to provide adequate room for maneuvering loaders and manure spreaders. Consider factors such as water drainage, roof runoff, and long-term impact of the location on vehicle or animal traffic.
Water drainage is a critical factor in selecting the location for a mini-pit. Do not locate the pit where runoff will flow towards the pit. Also divert all rainwater from the roof of the freestall barn so that it will not enter the mini-pit. A concrete or earthen drainage channel can be used between the barn and the mini-pit to divert runoff water. If significant attention is not given to drainage the short-term storage will fill with rainwater.
Mini-pits can be located on the end of the alleys inside the freestall barn. Covering the mini-pit with a roof has the advantage of limiting the amount of rain and snow that will enter the mini-pit, and will prevent an overflow caused by rain. An old hay shed or similar building could be used to cover a large mini-pit if it is near the site of the proposed freestall barn.
Gravity flow, flush, pumps, and mechanical alley scrapers do not handle frozen manure well. Cleaning the alleys with a skid steer loader, and pushing frozen manure to a mini-pit can serve as a back-up to any of these systems for 10 to 40 days per year in cold freestall barns. During mild winter weather manure is often hauled to flat cropland. Development of a well organized long-term site plan will allow the construction of a mini-pit in a location that will allow it to serve as storage for 10 to 40 days of frozen manure once the long-term storage is constructed. Locate the mini-pit so that it will not interfere with farm vehicle, or cow traffic.
Poured-in-place concrete is a popular material for mini-pits. However, prefabricated panels can be used for the sidewalls. Walls are typically 6 inches thick and steel reinforced. Concrete wall design is provided in the following publications:
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A mini-pit is typically sized to provide 1 to 4 weeks of storage. However, producers that use sand bedding in freestalls have constructed ramped concrete pits to provide 2 to 4 months storage. Dimensions and storage capacities of several mini-pits are given in Tables 1a through 1d.
Table 1. Mini-pit dimensions and storage volumes (see Figure 1 for
location of dimensions).
(Assumptions: 3 ft3/cow/day; 6 inch free board)
Table 1a.
Depth, D = 3 ft
Ramp Length (RL) = 30 ft.
Bottom Total Storage Storage for
Width, W Length, BL Length Volume 100 cows
(ft) (ft) (ft) (ft3) (days)
-----------------------------------------------------------
20 20 50 1,750 5.8
40 70 2,750 9.2
60 90 3,750 12.5
24 20 50 2,100 7.0
40 70 3,300 11.0
60 90 4,500 15.0
36 20 50 3,150 10.5
40 70 4,950 16.5
60 90 6,750 22.5
Table 1b.
Depth, D = 4 ft
Ramp Length (RL) = 40 ft.
Bottom Total Storage Storage for
Width, W Length, BL Length Volume 100 cows
(ft) (ft) (ft) (ft3) (days)
-----------------------------------------------------------
20 20 60 2,800 9.3
40 80 4,200 14.0
60 100 5,600 18.7
24 20 60 3,360 11.2
40 80 5,040 16.8
60 100 6,720 22.4
80 120 8,400 28.0
36 20 60 5,040 16.8
40 80 7,560 25.2
60 100 10,080 33.6
80 120 12,600 42.0
100 140 15,120 50.4
Table 1c.
Depth, D = 5 ft
Ramp Length (RL) = 50 ft.
Bottom Total Storage Storage for
Width, W Length, BL Length Volume 100 cows
(ft) (ft) (ft) (ft3) (days)
-----------------------------------------------------------
20 20 70 4,050 13.5
40 90 5,850 19.5
60 110 7,650 25.5
24 20 70 4,860 16.2
40 90 7,020 23.4
60 110 9,180 30.6
80 130 11,340 37.8
36 20 70 7,290 24.3
40 90 10,530 35.1
60 110 13,770 45.9
80 130 17,010 56.7
100 150 20,250 67.5
120 170 23,490 78.3
Table 1d.
Depth, D = 6 ft
Ramp Length (RL) = 60 ft.
Bottom Total Storage Storage for
Width, W Length, BL Length Volume 100 cows
(ft) (ft) (ft) (ft3) (days)
-----------------------------------------------------------
24 40 100 9,240 30.8
60 120 11,880 39.6
80 140 14,520 48.4
100 160 17,160 57.2
36 40 100 13,860 46.2
60 120 17,820 59.4
80 140 21,780 72.6
100 160 25,740 85.8
120 180 29,700 99.0
140 200 33,660 112.2
Slope the ramp to drop a maximum of 1 ft per 10 ft of ramp length to allow convenient access with a skid-steer or large bucket loader. If the ramp is too steep then the loader will not be able to drive up the ramp during warm weather. Providing grooves across the ramp will improve traction.
Provide a steel pipe fence on three sides of the mini-pit. Position the bottom rail so that manure can be pushed beneath the fence (see Figure 1). Manure can be pushed into the pit from all three sides and will allow frozen manure to be pushed into the pit in multiple locations. Provide additional security fencing that will keep children and livestock from entering the pit area.
Manure is scraped from the alleys into the pit using a skid-steer loader, or tractor and bucket. Mini-pits are intended to provide short-term storage for manure from freestall facilities. Parlor and milk house wastewater should not be included. Addition of wastewater will make the manure more difficult to remove from the pit with a bucket loader. If wastewater is mixed with sand-laden manure large amounts of sand will settle out, and cleaning out the pit will be more time consuming. If desired, a pto-driven, manure auger (12 to 15 inches in diameter) can be used to quickly lift sloppy manure from the pit into a spreader during most of the year. A portion of the manure solids (and sand) will be deposited on the ramp and bottom, but they can be easily scraped toward the auger or removed with a bucket loader. A loader must be used during winter.
Manure that has been spread on frozen ground can be source of surface water pollution in the spring when the snow melts. Manure should only be spread on fields with a slope of 6% or less when the ground is frozen (Source: Running Your Feedlot, Minnesota Pollution Control Agency). Set aside the flatest fields for winter manuring spreading. Do not spread manure on fields, or portions of fields that are closer than 300 ft from surface water during winter. Surface water is defined as any lake, river, stream, wetland, tile inlet, or drainage ditch.
Dairy producers that spread manure every 1 to 4 weeks should carefully plan crop rotations, to provide land for spreading during the growing season. Some practices that can free up cropland for spreading during the growing season are:
Manure that is surface spread on cropland could be a source of surface water pollution during the next heavy rain. In general, manure should not be surface spread on cropland that is closer than 200 ft from surface water during the growing season. Manure should also not be applied close to wells (200 ft), or sinkholes (100 ft).
Mini-pits can provide a method to improve the labor efficiency of handling manure in freestall barns that would normally use daily haul. In the future, a long-term manure storage can be built and the mini-pit can serve as a place to store 10 to 40 days of frozen manure in the winter. Dairy producers that use sand bedding in freestalls may want to consider using a mini-pit to provide short-term storage for sand-laden manure.
