Soil microbial and nutrient responses over seven years of organic apple orchard maturation

Seven years of twelve treatment combinations of annual compost, wood chips, shredded paper mulch, or mow-and-blow ground cover and poultry litter, organic commercial, or no fertilizer control surface applications on soil decomposition and microbial activity were evaluated in an organic apple orchard. Because soil amendments were surface applied, microbial biomass, enzyme activities, organic matter, dissolved organic carbon (DOC) and dissolved total nitrogen (N), ammonium-N, and nitrate-N concentrations were measured in March from 2007 to 2013 at 0–0.1 and 0.1–0.3 m soil depths where biochemical activity and nutrient availability were expected to be greatest and where tree roots were expected to be located. Ground covers were applied by volume based on horticulture management and these applications rather than fertilizers were stronger drivers of soil nutrient and microbial property responses. Dehydrogenase and β-glucosaminidase activities were 1.5 times greater in 2008 and 2009, respectively, under mow-and-blow as compared to other ground covers. Enzymes may be sensitive indicators separating living and non-living mulch effects on soil during establishment of fruit tree orchards in the southeastern U.S. Organic matter (OM) and soil water content increased in all ground covers during the study. At greatest differences, soil OM and DOC were more than twice and dissolved total N and nitrate-N were more than three and five times greater in compost than other ground cover treatments. Relative differences between compost and other ground covers did not persist to the same extent during the seven years. Orchard floor management may need different strategies during different stages of orchard development.