In organic apple orchards, one of the most serious challenges for growers is determining ways to limit weed competition while improving soil quality and ensuring high yields of quality apples. Scientists from the Swedish University of Agricultural Sciences published a study of orchard floor management systems (HortScience, March 2015) that revealed the benefits of using "sandwich systems" in organic orchards.
Ibrahim I. Tahir, Sven-Erik Svensson, and David Hansson investigated different orchard management systems in an organic apple orchard adapted to a cool climate, and evaluated the systems' effects on weed management, soil nutrient content, and soil physical conditions. The study also determined how each management system affected apple yield, quality, and storability. The results revealed strategies that could replace standard mechanical tillage with new floor management systems.
According to the study, the "sandwich" system was developed in Switzerland as a method of combining living mulch with modified tillage. Sandwich systems feature annual or perennial crops sown in a narrow strip within the tree row; the soil to each side of this strip is tilled. "This method has been reported to show the lowest costs for practical weed control without any negative effect on tree performance and yield, and can also decrease pests and diseases and increase biodiversity, improve soil conditions, and enhance nutrient cycling," the authors explained. "There are several challenges to sandwich systems, such as choosing living mulch mixtures that have minimal competition, avoiding rodent problems, and adjusting vegetation growth without any negative effects on apple yield, fruit quality, and storability."
For their research the scientists compared standard mechanical cultivation with four different orchard floor management systems: acetic acid, living mulch, a sandwich system during the growing season, and a sandwich system during the whole year.
The acetic acid treatment showed good weed suppression without any amendatory effect on soil conditions, fruit quality, or tree performance. The living mulch and sandwich system during the growing season systems increased soil respiration, decreased tree vigor, and improved fruit quality, but had no sufficient influence on weed competition and thus decreased fruit yield.
The sandwich system during the whole year (SSW) showed the most promise. "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," the authors said.
"The SSW strategy can be a useful alternative to mechanical cultivation if weak vegetation is established in narrow strips under the tree rows and nitrogen in the soil is continually adjusted during the season," they said.
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