Groundcover Management System and Nutrient Source Impact Physical Soil Quality Indicators in an Organically Managed Apple Orchard

In March 2006, four groundcover management systems (GMS) and two nutrient sources (NS) were evaluated for their ability to alter the physical condition of newly-established orchard soil. Annual applications of municipal green compost (GC), shredded office paper (SP), wood chips (WC), and mow-blow (MB) grass mulch were utilized as GMS, and NS were supplied to trees from composted poultry litter and a commercial organic fertilizer in a 4x3 factorial study. An established, conventionally-managed orchard was located on the same soil series and adjacent to the organic research orchard. Physical soil characteristics were measured from the conventional orchard providing a subjective comparison of orchard management systems. Soil organic matter averaged 1.5% at organic orchard establishment. By 2012, soil organic matter increased to 5.6% in GC while all other treatments had approximately doubled, with values in MB, SP, and WC increasing to 2.6%, 3.0%, and 3.2%, respectively. The change in soil organic matter impacted physical soil characteristics. Mow-blow treatments provided the least change in physical soil quality and served as an informal control to which other GMS were compared. Greatest increases in estimated plant available water were noted in treatments receiving GC applied alone (18.1%) or in combination with commercial fertilizer (17.7%). Bulk density values averaged 1.34 g·cm³ in 2006 but decreased in following years for all GMS. Most significant reductions occurred in WC (1.01 g·cm^-3) and GC (1.02 g·cm^-3) treatments. Increases were observed in the formation of large water stable macroaggregates. Green compost treatments resulted in a 4200% increase in 2.0 to 4.0 mm water stable aggregates taken from the upper 7.5 cm of soil. Infiltration rate was calculated for all treatments based on time required for complete drainage and over the total 18 minute drainage time. The greatest infiltration rate was associated with SP treatments (11.1 mm/min) and was slowest in WC treatments (3.1 mm/min). Soil organic matter measured 2.7% in the conventional orchard in June 2012, and only MB (2.6%) was lower. With the exception of GC applied alone (18.1%) or in combination with commercial organic fertilizer (17.7%), estimated plant available water capacity was lower in the organic orchard than in the conventional orchard (17.2%). Soil bulk density was higher in the conventional orchard (1.27 g·cm^-3) than measured in all GMS treatments. All GMS treatments resulted in greater water stable aggregate formation. Only in WC was water infiltration slower than in the conventional orchard; otherwise GMS enhanced infiltration rate.