The author has studied the relations between the yield of the poplar (Populus nigra var. italica Muenchh.) and some of the factors that could possibly have influenced it.
Highly significant correlation was found between the yield and the quantity of nitrate nitrogen existing in the soil.
No correlation was found between the yield and: clearings, depth of soil, and the available quantities of P2O5, K2O, an Ca in the soil.