Biomass production and root distribution of Gmelina arborea under an agrisilviculture system in subhumid tropics of Central India

A study of an agrisilviculture system comprising Gmelina arborea and soybean (Glycine max) was conducted in the subhumid region of Central India. Above- and below-ground biomass production and distribution of coarse and fine roots were studied in 4-year-old G. arborea, planted at a spacing of 2 x 2 m, 2 x 3 m, 2 x 4 m and 2 x 5 m. The total biomass varied from 10.89 Mg ha(-1) to 3.65 Mg ha(-1) depending on the tree density. Among the different tree components, stemwood contributed maximum biomass (54.3 - 79.4%), followed by branches and leaves. Root distribution pattern showed that most of the coarse roots were distributed in the top 40 cm of soil, whereas fine roots were concentrated in the top 20 cm. Coarse root biomass decreased with an increase in spacing. The spread of roots was asymmetrical in trees planted at 2 x 2 m and 2 x 3 m spacings, while it was symmetrical in trees planted at wide spacings. No significant difference was observed in the fine root biomass in different stands. The root: shoot ratio increased with an increase in spacing. Crop ( soybean) growth and productivity varied significantly and it increased with a decrease in tree density. Soybean yield varied between 1.5 Mg ha(-1) to 2.1 Mg ha(-1). The role of root architecture of G. arborea trees on productivity of crops under agri-silviculture system is discussed.