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| Figure 1. Shaping beds before laying mulch. |
The use of plastic mulch is a common practice for nearly all strawberry growers and most vegetable growers. It is usually combined with the use of a fumigant and drip irrigation. Installing the mulch is easier than it used to be when mulch was installed by hand, but it can be challenging.
Preparation
Preparation for laying mulch starts well before the mulch is installed. Many farmers grow a cover crop on the beds the previous season and incorporate the green manure into the beds as they are prepared for the mulch. The rough beds must be made with a disk bedder or occasionally a middlebuster. It is common to apply preplant granular fertilizer before installing the mulch. The fertilizer can be knifed into the beds, but it is just as effective to broadcast the fertilizer before bedding and then use the bedding operation to concentrate the fertilizer in the beds.
Bed Shaping
The beds must be firmed and shaped, either before the mulch laying operation (Figure 1) or as part of the operation. The top and sides of the beds must be firm, and there should be no depressions on the bed top to hold water on the mulch. Some growers install the plastic drip tape before laying the mulch (Figure 2), but it is more commonly done simultaneously with the mulch laying. It is important to completely cover over the drip tubing furrow to avoid a depression on the bed top.
Fumigation
It is usually best to apply the fumigant with the mulch layer so that the fumigant is immediately sealed before it can vaporize. Occasionally a grower will use two tractors, one knifing in the fumigant and the second tractor immediately behind laying mulch. This procedure risks not getting the fumigant sealed promptly and also exposes the driver of the second tractor and the worker on the mulch layer to more fumigant. As with the drip irrigation knives, it is important that the furrows in the bed from the fumigant knives be closed. Many mulch layers have either compression panels on the sides or a complete bed shaper pan to squeeze the bed and seal the furrows ahead of the plastic mulch. Some inexpensive mulch layers do not have this and merely rely on having a firm bed ahead of the mulch layer.
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| Figure 2. Shaping beds and installing drip irrigation tape before laying mulch. |
p>Laying the Mulch
Adjusting a mulch layer is an art. The shaping components of the mulch layer (if so equipped) must be adjusted in both dimensions to deliver a firm bed to the mulch area. There is usually some means of cutting a small trench or furrow at the bottom of the bed sides to receive the sides of the plastic sheet. Rubber tires, frequently smooth, are run on top of the sides of the plastic at a small angle to hold the plastic down and stretch it over the bed. Single disks (or sometimes shovels) on each side are then used to throw soil over the sides of the plastic in the furrow – referred to as the cup. This soil is what holds the plastic mulch in place. Adjusting the covering disks is probably the most critical part of the process. It is also important to maintain the proper fore-and-aft angle on the mulch layer for all of the components to function properly. Some high-end mulch layers have four gage wheels to help with this.
Safety Issues
Aside from the usual mechanical safety considerations, chemical safety is a major issue since most fumigants are highly toxic. Be sure that workers are not exposed to excessive amounts of fumigant. All workers should wear the personal protective equipment mandated by EPA on the fumigant label. Careful operation can help reduce the problem. For instance, not turning on the fumigant until the knives are in the soil and then turning it off before the knives are raised will help a great d
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| Figure 3. Plastic mulch layer in operation. |
eal. Installing a solenoid or motor valve down near the knives will reduce the amount of excess fumigant that drains out at the field ends.
Selecting a Mulch Layer
Commercially available mulch layers range from simple light-duty machines to heavy, rigid implements with a corresponding range of prices. The light-duty mulch layers can work satisfactorily if properly adjusted and used, but keeping them in adjustment is much more difficult. The heavy-duty machines tend to be more reliable and cause less trouble – but require a larger tractor and are more expensive.
Laying plastic mulch along with the accompanying drip tube and fumigant is a major expense and technical challenge for most growers. Properly adjusting and using a good mulch layer can minimize problems. For most small growers, a good custom operator is often the best solution.