The use of plastic mulch is a common practice for strawberry and vegetable growers, but there are two major problems with plastic mulch: it is expensive to install and at some point it has to be removed from the field. Several machines can help simplify removing it.
Traditional MethodsThe traditional method of removing plastic mulch was to first loosen the mulch from the “cup” on each side of the bed by passing a cultivator sweep under the cup and then pick up the mulch by hand. Picking up mulch by hand is a filthy and strenuous task.
Mulch LiftersSeveral companies now offer mulch lifters (Figures 1 & 2) that do a better job of loosening the plastic mulch than a simple sweep. These lifters typically have coulters that run beside the beds to cut any weeds or plant residue and loosen the soil, followed by one-sided blades that run under the cup and under much of the bed to further loosen the soil and lift the plastic mulch. Guides on the back of the blades lift the plastic in the air to allow the loosened soil to fall off. Some of the soil tends to fall back onto the center of the plastic sheet, making the plastic difficult to pick up. A coulter running down the center of the bed slices the plastic strip in half, allowing the soil on the center of the plastic to fall through when the plastic is later picked up.
Plastic CollectionAfter the plastic is loosened and lifted, some growers pick up the plastic by hand; however, there are several machines available to pick up the plastic. The most common design has a powered spool to roll up the plastic (Figure 3). In most cases, a worker has to tie the strip of plastic to the spool at the beginning of the row and then the plastic can be rolled up. A major problem with this type of pickup device is that as the spool fills, its diameter increases and thus the peripheral speed of the plastic increases. As the spool fills, either the tractor ground speed must constantly increase or the spool rotational speed must constantly decrease. This problem is addressed in different ways on different models of mulch collectors. Some use a belt drive to the spool and allow the belt to slip to maintain constant tension on the plastic. Others have a variable-speed valve in the hydraulic line to the spool motor that must be manually adjusted (constantly) by an operator riding on the machine. A design developed by the LSU AgCenter senses the tension on the plastic and automatically adjusts spool speed to provide relatively uniform torque loading on the spool. An entirely different design uses rollers to feed the plastic sheet into a big wire cage instead of rolling it up.
Using Lifters and CollectorsIt is possible to combine a lifter and collector into a one-pass machine. Although this seems efficient, it is not necessarily desirable, at least in humid climates like Louisiana. Collecting the mulch is much easier when the loosened soil on top of the mulch is completely dry and thus doesn’t stick to the plastic mulch. In the humid South, it is unusual for the soil in the cup to be that dry, so it is helpful to run the lifter when the soil is reasonably dry, then allow the loosened soil on top of the mulch to dry further before attempting to pick up the plastic.
Trash RemovalRemoval of plant residue from the mulch before attempting to lift the mulch will make the operation much more efficient and will reduce the volume and weight of the collected product. A rotary cutter or other mower run as low as possible (without cutting the mulch) before lifting will help.
ProblemsBy far the most common problem in lifting and removing plastic mulch is tearing of the plastic. If the plastic holds together and comes off in one long strip, the task is easy, but in too many cases the plastic tears into small pieces that have to be picked up individually. Removing plant residue, proper lifting and careful collecting will help, but in some cases the plastic is just too weak or brittle and tears too easily. When that happens, picking up the pieces by hand is about the only option.
Removal of plastic mulch continues to be a problem for strawberry and vegetable growers. Some machines can help with the process. Under ideal conditions, the process can be mechanized, but problems remain, primarily because of the tearing of the plastic.
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