PHYSICAL CONDITIONS IN PEAT/PERLITE MIXTURES SUBJECTED TO DIFFERENT IRRIGATION REGIMES
Irrigation regimes were defined in relation to the volume of liquid in the substrates at container capacity when the experiment started (initially). Single pots were re-irrigated with nutrient solution as 10, 30, 50 and 70 % of that volume of liquid was consumed.
Growth substrate volume and bulk density, and the fraction of perlite mixed with the peat were measured initially and at the termination of the experiment (finally). The volume fraction of gas filled pores was obtained gravimetrically at least once a day to describe changes in the liquid status of the growth substrates.
The volume of substrate stayed constant in all irrigation regimes during the experimental period. The bulk density was independent of the fraction of perlite, but it was lower finally than initially for substrates subjected to the most frequent irrigation.
The initial volume fraction of gas filled pores was negatively correlated with the initial bulk density, and the linear regressions depended on the fraction of perlite. The volume fraction of gas filled pores at container capacity (fgcc) increased during the experiment from .33 to .50 ml ml-1 for substrates subjected to the most dry conditions, and from .33 to .41 ml ml-1 in regimes allowing 30 and 50 % liquid losses. For substrates subjected to the least dry conditions, fgcc decreased from .30 to .26 ml ml-1.
Initial and final fgcc was positively correlated. The linear regressions were different for the different irrigation regimes as indicated by their average changes described above.