Root growth potential and early field performance of Gmelina arborea intercropped with Zea mays

Three continuous studies were undertaken to characterize root growth potential (RGP) of Gmelina arborea based on provenance and to evaluate RGP's suitability as a measure of seedling quantity through field trials as affected by distance of planting and provenance. Carbon storage of the farming system was estimated through field measurements. The nursery experiment showed significant variations in all morphological characteristic of seedlings of Gmelina by provenance. Seeds from Candeleria, Quezon and Kabacan, Cotabato were significantly different in all morphological trait measured compared with seeds from Davao del Sur and Arakan, Cotabato. The RGP in terms of first order lateral roots(FOLR) was found to be positively correlated with root collar diameter, primary root length, stem height and root shoot ratio. The frequency distribution of FOLR on the other hand was found to be normally distributed. Seedlings with 18 FOLR counted the most from a range of 3 to 35. There were three natural FOLR groupings established: R1 (0-10); R2 (11-20); and R3 (21-30+). The field trial revealed significant differences in the growth of Gmelina after one year. Strong genetic control over height, basal area, and biomass were observed. Seeds from Quezon were significantly different in terms of merchantable and total heights compared to those from Cotabato and Davao del Sur. While in terms of basal area and biomass, Quezon and Cotabato seeds did not differ significantly. On the other hand, the three provenance did not vary significantly in terms of DBH, tree volume, and survival. Distance of planting also insignificantly affect height, diameter growth and survival of the tree. However, basal area, tree volume and biomass varied significantly. Root classes affected tree diameter, total height, percent survival, and volume significantly. All factors did not show any significant variation on basal area, and merchantable height. Root classes were found to be positively and significantly correlated with DBH, basal area, and root biomass. The performance of the intercropped Zea mays varied significantly in all agronomic and morphological characters as affected by tree spacing but not by RGP classes. The monocropped corn significantly performed better in all traits compared to those interplanted with the Gmelina.