MINI-PITS: A SHORT-TERM MANURE STORAGE ALTERNATIVE FOR FREESTALL DAIRY FACILITIES THAT HAUL DAILY OR USE SAND BEDDING

John P. Chastain
Agricultural and Biological Engineering
Clemson University

Introduction

Many dairy producers in South Carolina land apply manure from freestall barns or outside lot areas daily. The primary advantage of a daily haul waste system is lower initial cost. However, daily application of dairy manure has the following disadvantages.
(1) Manure must be spread during rainy weather. Application of manure on wet fields or pastures can damage forage stands, degrade soil structure, and create polluted runoff that could pollute surface water.
(2) Manure can not always be spread of forage or crop land at a time when the nitrogen can be taken up by the plants. For example, if manure nitrogen is applied several weeks before planting corn or when hay crops are not actively growing then a portion of the nitrogen may leach out of the plant root zone. Ground water pollution could occur in regions of South Carolina that have sandy soils.
(3) Manure must be removed from freestall alleys at least twice each day to keep cows clean. If a short-term structure is not provided 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. As a result, cow cleanliness suffers if some sort of manure containment is not provided.
(4) Hauling manure daily is not an efficient use of labor on a dairy farm. Short-term storages that allow manure to be hauled every 2 to 8 weeks are more efficient.

A ramped, concrete mini-pit (shown in Figure 1) can provide a low-cost, short-term storage that will improve labor efficiency, allow implementation of a environmentally sound manure utilization plan, 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.

Location of Mini-pits

A mini-pit should be located off the end of a 2 or 3-row freestall barn or south of the cross alley of a drive-through barn. Locate the mini-pit so that it will not interfere with farm vehicle, or cow traffic. 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.

A mini-pit to provide for 2 weeks of covered storage for the manure produced by 100 cows. Click here for a larger photo.

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 use gutters or channels on grade to divert all rainwater from the roof of the freestall barn so that it will not enter the mini-pit. 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 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.

Construction

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:
Farm and Home Concrete Handbook (MWPS-35); and
Concrete Manure Storages Handbook (MWPS-36).
Both of these publications can be obtained from the Agricultural and Biological Engineering Department at Clemson University (864-656-3167).

Storage Capacity
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. In South Carolina the minimum storage period that is desirable is 2 weeks to allow storage of all manure during and after periods of heavy rainfall. The actual storage period needed for a given farm will depend on the diversity of the crops and forages grown. Provide storage capacity for the longest period when manure can not be applied based on the waste management plan of the farm.

Dairy producers that plan to spread manure every 2 to 4 weeks should carefully plan crop rotations, to provide land for spreading during the growing season. Some practices that can provide multiple ³windows² to spread manure throughout the year are:

double or triple crop all row crop fields,
spread manure after cutting hay,
spread manure on pasture,
plant a variety of annual and perennial forage crops that will provide nutrient
uptake 9 to 12 months out of the year,
contract with neighbors to spread manure on crop or forage land once or twice
each year, or
spread a portion of the manure on forest land to increase wood production.
Dimensions and storage capacities of several mini-pits are given in the Tables .

Ramp Slope
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.

Safety Fence
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.

Filling and Emptying

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 PTO driven auger can be used to unload dairy manure from mini-pits. Click here for a larger photo.

Summary

Mini-pits can provide a method to improve the labor efficiency of handling manure in freestall barns that would normally use daily haul. The minimum storage period that is recommended in South Carolina is 2 weeks. However, the mini-pit must be sized to store manure for the longest period for which manure can not be spread. 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.

Return to The Land Application of Animal Manure.