Development of a model system to investigate soil health in pome and stone fruit using potted plants

An understanding of how plants respond to changes in soil health is required to establish a relationship between soil characteristics (chemical, physical and biological) and plant performance. Pot trials are a useful tool to reduce complexity and field variability and provide results over a relatively short time period. Trials were initiated to firstly refine the technique of the bioassay and to adapt methodology, which was then used in bioassays investigating soil health aspect. A trial was established to investigate the effect of mulching on soil health, by sampling three different layers in the top 0-22.5 cm soil beneath a mulch and no mulch in the same orchard. In addition, long term apple replant disease (ARD) field treatment and the effect on plant performance and soil properties was investigated in a bioassay.

Results indicated that biological soil management practices, such as mulching and compost application, have a positive effect on soil chemical properties, as well as soil carbon content. Significant increases in total plant biomass in seedlings from the 0-7.5 cm soil layer directly underneath the mulch compared to the 12.5-22 cm layer, as well as 7.5-22 cm soil layers in non-mulched orchard areas, indicates that mulching can improve the soils ability to sustain growth. A higher growth potential was also implied for the mulch layer. Results also indicated the presence of a biotic growth-limiting factor present mainly in the top soil layer (0-7.5 cm) and is consistent with the growth retarding effects experienced with replant disorders which are generally of biological cause and concentrated in the top 10 cm of soil. This is in agreement with results from the ARD bioassay. In addition, plant growth in biologically managed soil (Biol) only improved in comparison to ARD soil when Biol was sterilised.

Results further indicated that the positive effect of MeBr does not persist for years after fumigation, once apples have been established in the soils, and the root exudates again start to select for the ARD pathogen complex. However, MeBrSt did not induce any growth increase compared to MeBr soil, which indicates that fumigation may have some long-term negative effect on soil properties (either biological or chemical) affecting growth negatively compared to ARDSt and BioSt soil which was not treated with MeBr previously.