Effect of conventional and organic orchard floor management practices on enzyme activities and microbial counts in a ‘Cripp’s Pink’/M7 apple orchard

Abstract

Organic (ORG) production practices are increasingly being used in South African apple orchards. Whether ORG orchard floor management practices differ in their effects on soil enzyme activities and microbial populations from conventional (CON) practices have not been adequately investigated, particularly with regard to soil chemical characteristics and orchard performance. To seek clarification a randomised field trial was carried out in the winter rainfall region of the Western Cape. In this trial ‘Cripps Pink’/M7 apple trees received straw mulch with compost (ORG) or synthetic fertiliser and herbicide (CON) in the tree rows. Soil microbial enzyme activities and microbial counts were determined by colorimetric assays and dilution plating, respectively. Activities of β-glucosidase, acid phosphatase and urease, and actinobacteria counts tended to be greater in the ORG than the CON treatments. Activities correlated positively with soil zinc and manganese concentrations and with leaf zinc, but negatively with soil copper. β-glucosidase and acid phosphatase activities also correlated negatively with ammonium and nitrate nitrogen in the soil, and with leaf nitrogen concentration. Yields decreased with increasing β-glucosidase and acid phosphatase activities. Therefore, although ORG practices increased soil microbiological activity relative to CON management, they did not improve yield.

Keywords: acid phosphatase, actinobacteria, β-glucosidase, heterotrophs, urease