Ground Cover Management and Nutrient Source Affect Soil and Foliar Nutrient Contents in an Organically Managed Apple Orchard in the Southern U.S.

Management of competitive vegetation and appropriate nutrient supply are issues facing organic fruit growers.  An experiment was established to evaluate the effects of four ground cover management systems [wood chips (WC), municipal green compost (GC), shredded white paper (SP), and mow-and-blow (MB)] and three nutrient source [untreated control (NF), composted poultry litter (PL), and commercial formulated fertilizer (CF)] on soil chemistry and nutrient content, soil quality, and tree performance in an organically managed orchard. The PL and CF were applied at equal (N) rates annually at prior to bloom.  Soil was sampled annually at two depths (0–10cm and 11–30cm) underneath the tree at multiple times for chemical properties and total extractable nutrients or available nutrient content (as determined by cation/anion membrane probes). Foliage was sampled at multiple times within each season.  The changes observed during the first 6 seasons of orchard establishment, transition, and maturity are presented.  From the initial planting year, soil pH increased from 6.5 and 6.4, to 7.2 and 7.2 for 0–10, and 11–30cm, respectively. The SP resulted in the significantly higher soil pH than other ground cover treatments.  Nutrient source did not consistently affected soil pH, although at several sampling dates, NF had higher soil pH at 0–10cm depth than soils receiving supplemental nutrition from an organic source. Soil NO₃ did not vary significantly with ground cover management treatment. Using PL as a nutrient source resulted in generally higher extractable NO₃ than NF or CF. Soils treated with GC had higher P at 0–10cm depths than other treatments beginning in year 3. Soils amended with PL had significantly higher P content.  Soil available N and NO₃ as detected by ionic membrane probes was significantly higher with GC than other treatments while there were few differences for NH₄. Soil available N and NO₃ was consistently higher with soils amended with CF and those not receiving any additional amendments were the lowest. Soil available P was consistently higher with MB and CF treatments. Foliar concentrations of all nutrients were in a sufficiency range. Although ground cover and nutrient treatments resulted in foliar nutrient contents early in young trees, there were few differences in the sixth growing season.  There were few interactions among ground cover management and nutrient source and typically ground cover treatments resulted in greater experimental variation than nutrient source for most nutrients in most years. Other nutrient responses and interactions will be discussed.