Hema Kasinathan Thesis May 1 2012.pdf - Atrium - University of ...

pore volume than the other growth media, not all of the pores are capable of holdingwater against gravity. The significant difference between Dobson’s results and the currentstudy is that soil compaction was not taken into account in their study.In the current study, analysis of soil physical properties showed that mineral soilhad a higher bulk density than muck soil and soil-less mix, as expected. There was anegative correlation between bulk density and micro-pore volume, and a positivecorrelation between bulk density and clubroot severity. Clubroot was more severe onmineral soil (high bulk density) than on muck soil and soil-less mix. Clubroot levels wereconsistently lower in soil-less mix (loose) and muck soil + soil-less mix. It is to be notedthat both the mineral mix and muck mix adjusted to have the same pore size. Thisindicates that besides soil pore volume or pore size, other soil properties played animportant role.The relationship between clubroot severity and soil bulk density has beenexamined for other root rot pathogens (Moots et al. 1988, Carter and Johnston 1989), butthis is the first report to establish a relationship between clubroot severity and bulkdensity. However, it is important to note that this relationship was not consistent acrossall of the experiments. Clubroot levels were higher in muck soil than in mineral soil inExperiment 1 and 2. Also, soil compaction was not included as a factor when the studywas initiated. Finally, the watering method was different in experiment 3 (sprayed withfine nozzle) than in the previous two experiments. The impact of change in wateringregime may have had an influence in soil compaction and subsequently in clubroot level.102