Sensitive indicators of soil organic matter sustainability in orchard floors of organic, conventional and integrated apple orchards in New Zealand

Major objectives of this study were to evaluate the effects of organic, con ventional and integrated orchard fruit production systems on the quality an d quantity of soil organic matter in orchard floors and to identify sensiti ve soil organic matter indicators. Seventeen different soil organic matter parameters were studied. These were soil aggregate stability (AS), total ni trogen (TN), total carbon (TC), carbon/nitrogen ratio, microbial biomass N (BN), microbial biomass C (BC), BC:BN; BC:TC; BN:TN; hot-water extractable C (HC), hot-water extractable carbohydrate (HCA), HCA:HC; humin N (hum N), humin C (hum C), hum C:TC; hum N:TN and potentially mineralizable N (Pot N) . They were based largely on soil organic matter characteristics and fracti ons extracted sequentially by different extractants from soils collected fr om the alleys and treelines of organic, conventional, and integrated grasse d-down apple orchard types from both commercial and experimental sites in C anterbury, New Zealand. A total of 12 apple orchards were investigated. Soi l samples collected From these orchards (0-75 mm depth) were analysed for T C, TN, BC, BN, Pot N, AS and also sequentially extracted for labile and sta ble soil organic matter fractions using cold and hot water, acid mixtures ( hydrochloric:hydroflouric acids, HCl:HF) and alkalis (sodium pyrophosphate and sodium hydroxide, Na4P2O7 and NaOH). Only TN, BN, and BN:TN showed sign ificant interaction effects and all these were associated with soil N. Over all, combining orchards according to similar management systems, results ob tained showed no significant differences between experimental and commercia l orchards. However, sensitive indicators capable of distinguishing signifi cant differences between different orchard management systems were BC, BC:T C and HCA:HC while HCA:HC distinguished significantly between treelines and alleys within each group of the same orchard type.