Effect of biological soil amendments on tree growth and microbial activity in pome fruit orchards
Agriculture is demanding more environmentally safe, sustainable production practices due to the adverse effect of conventional practices on soil biological activity and diversity. Soil rehabilitation and root growth stimulation is also of prime importance in orchards suffering from apple replant disease (ARD). We hypothesised that the application of organic matter, soil microbial inoculants and biostimulants can improve soil microbial activity and feeder root development, thereby having a positive effect on tree growth in newly established orchards, especially ARD sites. Furthermore, the effect of the various treatments on soil microbial community activity was examined, using soil enzyme assays and conventional microbial plate counts. At two sites, biological soil amendments that performed the best in terms of growth increase were compost in combination with compost extract and application of beneficial bacteria (Biostart®). However, results from ARD trials were inconsistent, with methyl bromide fumigation promoting best growth. Soil enzyme assays indicated significant changes in soil microbial activity after 3 years, with fumigated soil showing lower activity. Soils amended with compost extracts or Biostart® had higher microbial activity. However, no simple relationship could be identified between tree performance and soil microbial activity.