The sites for the placement of tested material samples which were marked out on the cultivated area were weeded first, and then the soil was removed to the depth of 20 cm and sieved through a wire mesh of 1�C2 cm to remove gravel and plant materials.

The sites for the placement of tested material samples which were marked out on the cultivated area were weeded first, and then the soil was removed to the depth of 20 cm and sieved through a wire mesh of 1�C2 cm to remove gravel and plant materials.