Soil and Nutrient Management in Organic Orchard Production.

Soil and nutrient management in organic orchard production

G.H. Neilsen¹, T. Forge¹, D. Neilsen¹ D. O'Gorman¹, D. Angers²and N. Bissonnette².

Agriculture and Agri-Food Canada¹, Pacific Agri-Food Research Centre, Summerland, British Columbia, Canada  V0H 1Z0 and  ²Soils and Crops Research and Development Centre, Sainte-Foy, Quebec, Canada  G1V 2J3

 Soil management strategies in organic production systems are designed to maintain soil fertility and increase soil biological activity and biodiversity by increasing soil organic matter content. A drip-irrigated, high density, ‘Ambrosia' apple (Malus domestica Borkh.) orchard planted at 1m x 4m in April 2006 was managed organically for the first six growing seasons and designed to assess soil and plant effects of four different  randomized soil management strategies, replicated six times in 10-tree plots. Treatments, applied within a 1.8 m strip centered  on the tree row, included 1) annual compost application to supply N, with mechanical tillage for weed control; 2) in-row application of alfalfa (Medicago sativa L.) mulch grown between the rows; 3) shredded bark mulch plus in row application of mixed hay grown between the rows; and 4) black plastic mulch, the last two treatments receiving annual fertigation of  fish based fertilizer sufficient to supply 5 g N /tree/yr.

                  Soil samples collected every second year indicated soil properties in the surface 0.1 m were strongly influenced by soil management. Higher soil organic matter and microbial biomass was measured for all treatments relative to soil from the herbicide strip of conventionally managed orchards. Organic matter concentration exceeded 7 %and apple fine root biomass was highest for the alfalfa and bark mulch treatments after 6 yrs. Soil beneath the bark mulch had highest organic matter, highest total , particulate and mineral associated –C, all characterized by high C/N ratios and increased  fungal feeding nematodes and  index of nematode functional diversity. Most vigorous trees were observed in the bark mulch treatment which had decreased leaf N but elevated leaf P and K associated with high soil levels of P-solubilizing  phosphate enzyme and absolute and relative levels of acetate –extractable K. Fruit yield and quality were minimally affected by soil management.