Root mass in plantations ofEucalyptus globulusin portugal in relation to soil characteristics

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Abstract
Root mass (living and dead roots) in two stands of blue gum (Eucalyptus globulus Labill.), near the town of Obidos in west‐central Portugal, was measured using an excavation method. One stand, at Alto do Vilão (AV), was 18 years old and was located on a sandy loam—clay loam. The other stand, at Bom Sucesso (BS), was 12 years old and was located on a sandy soil. AV was planted after superficial ploughing, while BS was planted after superficial ploughing followed by the creation of deep furrows in rows. Total root mass was significantly higher at BS (23 t ha−1) than at AV (12 t ha−1). At BS total root mass was significantly higher within tree rows than between rows. The difference between the stands at AV and BS can probably be explained by differences in bulk density of the soil, since the less dense soil at BS may have allowed roots to penetrate a greater soil volume. The difference between within‐and between‐row estimates of root mass at BS can probably be explained by deeper soil preparation, which broke a hardpan and mixed the soil horizons. The penetration was more pronounced within rows than between rows. Fine‐root mass was significantly higher at BS (11 t ha−1) than at AV (6 t ha−1), but this finding could not be explained by differences in bulk density. We suggested that the amount of fine roots was related to water and nutrient availability within the soil surface layer. Above‐ground biomass was estimated to be 267 t ha−1 at AV and 190 t ha−1 at BS. Above‐ground net primary‐production was estimated to be 14.7 and 20.4 t ha−1 in AV and BS, respectively. Root mass seemed to be positively correlated with above‐ground net primary‐production rather than with biomass.