THEORETICAL MODEL FOR ESTIMATING THE DENSITY ROOT TWO WOODY SPECIES

Abstract

Root studies on woody species are necessary to predict or to mathematically model plant growth under different management and/or environmental conditions. Nevertheless, the methodology to calculate root density (Lv) is laborious and time consuming. An alternative and quick method is based on assessment of the root number (N) that intercept a soil profile, since it can be converted into Lv due to the theoretical relationship Lv= 2N. The present study was aimed at evaluating a theoretical model to estimate root density of two woody species (i.e. L. leucocephala and Z. formosa) using eleven-months-old plants sown into PVC tubes (15 cm diameter) containing a luvisol-sand mixture (2:1). When plants reached nine months old, four PVC tubes per species were selected at random; then three 10cm-PVC-layer, containing the soil mixture and roots, were taken from each PVC tube starting from the upper part for both species. Root number were measured from three cube sizes (i.e. 10, 7.5 and 5 cm per side) and three soil profiles (i.e. X, Y and Z). Subsequently, root density was measured using image digitalization and relate with the predicted density from the mathematical model. It was found that, N was different between species for each soil profile, and it did not depend on the profile size, except for the Z profile (P<0.001), meaning that the growth preference was vertical rather than horizontal for both species. Root density and number correlation coefficients were different (P<0.01) between species. The present study was undertaken mainly to find a relationship between Lv mathematically predicted and the measured Lv using the root washing method. Should this relationship would be high, then it would have demonstrated that the mathematical model could be used instead of the root washing method, which is laborious and time consuming. However, it was found that the correlation was low, since it only allows 35 and 37% prediction for L. leucocephala and Z. formosa, respectively.