Fig. 5. Matric head measured at mid container height within the three substrates at the beginning of the experiment and before harvest of the Sp60B30 treatment. Each value is the mean of three replicates. The star indicates significant differences in matric head between the Sp30B60 substrate and the other two substrates and the error bars are the standard deviation of the raw data, for the first and the last measurements, to provide an idea of the minimum and maximum variability observed between measurements.