FIG. 16. Root development after fertilization in a stand of Pinus silvestris on a devastated sandy soil of average productivity. Represented as number of roots less than 1 mm in diameter per 1 dm2 wall area of soil profile: 0 - 0 = 54-year-old stand without fertilization; X - X = 57-year-old stand without fertilization; . - . -. = 57-year-old stand fertilized in 1962 with N-P-K and Mg (80 kg of nitrogen per hectare) and in 1963 with 80 kg of nitrogen per hectare (data from Buchholz and Neumann, 1964).