The variation in growth of the fine roots of blue gum (E. globulus Labill. ssp. globulus) in the 0-40 cm soil layer was studies from March 1982-March 1983 at Quinta do Furaduoro, Obidos, Portugal. A mesh bag method was used; bags of nylon net were inserted into a clay soil and a sandy soil and filled with root-free soil. They were resampled after 2, 4, 6 and 12 mo. in both places and, in a separate series in the sandy soil every 2nd mo. throughout the year. The ingrowth of roots was high during the winter months but there was also a surprisingly high ingrowth during the spring-early summer period. There was also some root growth during the driest part of the year viz. July-Sept. The amount of fine roots reached a maximum of about 260 g dw m-2 after about 6 mo. in the sandy soil, whereas it took at least 12 mo. to reach the somewhat higher level of 450 g dw m-2 in the clay soil. At that level the decomposition of dead roots was expected to equal the formation of new roots. Dead roots appeared after only 2 mo. There was a higher proportion of dead roots in the clay soil than in the sandy soil, 35% as compared with 20% on an average, which indicates a slower decomposition or a higher mortality at equal decomposition rates in the clay than and in the sandy soil. The present data gives an indication of a minimum fine root production in mature Eucalyptus stands of at least 600 g dw m-2 yr-1.
