Plastic Tunnel and Mulch Laying Machine

James F. Thompson, Agricultural Engineer
Clay R. Brooks, Development Engineer
Agricultural Engineering Extension
University of California, Davis, CA 95616

Tunnels made of clear polyethylene sheets are used to allow early production of field vegetable crops. Tunnels increase soil temperature compared to uncovered planting and help protect against frost damage. Tunnels can be installed completely by hand but many growers have found that a simple machine, built in a farm shop, will reduce overall costs and assist in producing a uniform installation that will resist wind damage.

Growers in California have developed a number of machines to lay plastic sheeting. Drawings on the following pages describe the key features in a well-designed machine.

The tunnel laying machine operates by opening two small furrows with 10" to 1211 disks. Three feet wide plastic sheeting is held on two sloping spindles. The sheeting feeds backward as the machine moves forward. One edge of each sheet is kept in the furrows by hold down wheels. The edges are covered with soil by rear disks and soil is firmed by rear press wheels.

The machine must be adjusted to bury 611 to 811 of plastic and cover it with 2" to 3" of soil. Burying less plastic or covering with less soil will increase the likelihood of wind pulling the plastic out of the ground.

Dimensions listed on the plan are good starting points but will need modification to suit specific field conditions. Factors such as forward speed, soil type, soil moisture, and slope of the field will affect component orientation and distance between components. Be sure to maintain a constant forward speed when adjusting the machine and using it.

Proper operation requires that the soil be well tilled with no clods, and as uniform as possible. If a furrow in the middle of the bed is used, it should be rough-formed with a shovel. The bed shaper will do the finish-forming just before the plastic is laid.

Some growers have replaced the first set of disks with furrow openers. Sandy soils will allow the use of a blade instead of the rear disks. A blade more uniformly covers the plastic and will provide a flat area immediately next to the plastic, making a better walk-way between tunnels.

The machine is operated at speeds of 3 to 5 miles per hour. It has a maximum capacity of 5 to 6 acres per day. A 35 horsepower tractor with a 3-point hitch is required.

The machine can be modified to lay plastic mulch by removing the two sloping spindles and replacing them with a single roll described in the details. Mulch would be laid first, then the tunnel installed with a second pass.

PLASTIC TUNNEL LAYER NOTES

1. Frame for 3-point hitch
2. Bed shaper (see detail)
3. 2" x 2" square tube
4. Spindle for plastic sheeting, made of 1" diameter pipe (see detail)
5. Soft hold down wheel for plastic sheeting, can be an inner tube mounted on a small wheel rim
6. 10" to 12" diameter disk mounted on a circular cross section shank
7. Rear press wheel, pneumatic tire or hard rubber wheel
8. 3/4" x 2/4" square tube
9. Tool bar
10. Roll of plastic sheeting

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