In fruit orchards, limiting weed competition, while improving soil quality, is very important to achieve high yields and high fruit quality. This can be especially challenging in organic orchards, where chemical herbicides are not permitted. One option that many organic growers are looking towards is the Swiss developed “Sandwich” method of orchard floor management. In this system, rows are mechanically tilled on both sides of the tree rows, while the center tree rows, left undisturbed, are used to grow flowering ground crop cover. No herbicides are used in this system, and as a bonus, the center, flowering, crops can entice and harbor beneficial insects.
“Sandwich” System Effects on Fruit Quality and Storage
Mechanically tilling strips on both sides of tree row can effectively reduce weed competition without using herbicides. A Swedish study in 2015 tested several different orchard floor management systems in an organic apple orchard, and found the sandwich system to be the most effective overall, with the lowest cost to the grower. The also tested using the sandwich system, solely during fruit production, and throughout the whole season, finding the whole season “Sandwich” system to be the most promising. The authors concluded,
Our analyses showed that the SSW eliminated vegetative cover competition, increased soil respiration, improved leaf and fruit calcium content and resulted in moderate leaf and fruit nitrogen content and tree growth reduction. Apples from these trees also had good quality and high storability.
Because of the high fruit quality and yield, we can conclude that root competition from the center, tree-line, vegetation row was not too much for the apple trees to overcome. The tilled strips opened up space for the trees’ roots to grow without weed competition.
Key Considerations with “Sandwich” System
There is some risk involved with “Sandwich” system for orchard floor management, deep cultivation can damage tree roots which may, in turn, reduce yields or fruit quality. Tillage is also know to decrease soil organic matter. However, newer cultivators such as the Wonder Weeder are much shallower and do not disturb roots or soil as deeply. Newer cultivator models are also able to incorporate soil amendments as a method to offset losses of soil organic matter.
Pest Control Benefits
The strip of vegetation in the tree row in this system can have additional benefits on pest control. Many flowering crops have been shown to increase biodiversity and attract and maintain beneficial insects, which can decrease populations of insect pests without pesticides. These flowers can be options for the tree row in the sandwich system, giving the grower an added benefit to the “Sandwich” system. This are may also be helpful in deterring vertebrate pests. Dr. David Granatstein at Washington State University has conducted studies that have proven Sweet Woodruff (Galium odoratum) to deter voles when used in a “sandwich” system. Having this row of vegetation which can be used for a variety of flower combinations, is a powerful tool for growers to be used for integrated pest management.