Farmland SoilWhen looking for agricultural land or desert land to reclaim in Egypt the first two things to check are salinity in water and soil. Additional soil tests should be done to determine pH value as well as presence (or absence) of minerals.
Conditions present in a specific area of land can determine which plants can grow in it naturally. It also helps realize which weeds can thrive there. All this helps when attempting to do permaculture.
It is crucial to measure pH value of a soil to know which plants can grow in it and to modify the pH value if necessary in order to accommodate for the needs of plants you would like to grow. The herb spiral might offer a continuum of different humidity levels as well as light intensities and pH values.
This might give a clue why the type of weeds that grow in a specific soil actually 'fix' that soil and improve it by balancing it out through making it more or less acidic, more or less compact and more or less saline.