Organic apple orchards benefit from green compost applications

In traditional apple orchards, effective management practices rely on two interrelated components: finding ways to manage competitive vegetation under the trees, and supplying important supplemental nutrition to trees. These factors are further complicated in organic management systems where limited tools are available, and producers need to meet the stringent soil fertility and crop nutrient management standards of the National Organic Program. University of Arkansas scientists published a study that includes recommendations for the use of various groundcover management systems for apple orchard floors. They say that selected management systems can improve soil quality in organically managed apple orchards.

Curt Rom, corresponding author of the study (published in HortScience), explained that orchards established on the weathered, acidic mineral soils in the Ozark Highlands must be strategically managed in order to meet the trees' nutritional requirements. "A common characteristic of Ozark Highland soils is a relatively low soil organic matter concentration, a condition that can have detrimental effects on orchard productivity," Rom said. A cross-disciplinary research team studied the impacts of groundcover management systems and nutrient source on soil characteristics, tree health and productivity, and insect, disease, and weed management. The experiments were performed in an organically managed apple orchard that was established in 2006 and continues today at the University of Arkansas' Agricultural Research and Extension Center in Fayetteville.

The researchers evaluated several under tree, in-row groundcover management systems, including shredded paper, wood chips, municipal green compost, and mow-blow. They also tested various nutrient sources (non-fertilized control, composted poultry litter, and pelletized organic commercial fertilizer). The groundcover systems and nutrients were analyzed for their respective effects on soil organic matter, carbon, and nitrogen concentration, and soil carbon and nitrogen sequestration.

The results showed that the use of various groundcover management systems as an orchard floor management tool can increase soil organic matter, total soil, and total nitrogen mineral soils, thereby improving soil quality. The greatest increases in these factors were associated with applications of green compost, which the authors say was a result of accelerated formation of carbon- and nitrogen-rich soil organic matter.

"Compared with conventional apple orchards managed with herbicides and fertilizers, green compost, wood chip, and shredded paper treatment may result in improved soil quality," the authors concluded. "However, care should be taken in organic apple production to ensure nutrients are not over applied, thereby protecting soil and water resources and maintaining the health of the orchard ecosystem."

According to Rom, the study has implications for sustainably and conventionally managed orchards as well as organic orchards, and demonstrates the sustainability of organically managed systems.

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