I already reported on an interesting experiment on growing tree seedlings, set up in Zanona (Cadiz/Andalucia/Spain). You may find this message in the November 2006 postings under Archives.
In May 1995, we showed the effect of the soil conditioner TerraCottem (TC) on seedlings of conifers. Seedlings were acquired in a nursery. Half of them were kept as control plants, the other half were treated with the TerraCottem soil conditioner (TC) at a dosage of 5 g TC per kg of potting soil. All plants got the same small volume of water at the same moment, so that a certain hydric stress was created for the seedlings under very dry conditions in this area of Southern Spain.
Six weeks later the dimensions of the seedlings were compared : length of the stem, length and volume of the root system.
TC-treated seedlings are significantly taller and their root system is longer and more voluminous (more rootlets, thus more adsorption of water and nutrients).
It is good to know that one can grow young trees with less water and, nevertheless, obtain taller and stronger seedlings, which are more resistant to water stress when planted out in the field.