Above- and below-ground biomass and allometry of Moringa oleifera and Ricinus communis grown in a compacted clayey soil

Moringa oleifera Lam. and Ricinus communis L. are species known for their ability to survive in different environments; however, analyses of their capabilities to develop and explore clayed compacted soils are still not well covered. This study compares above- and below-ground development of Ricinus and Moringa in a subtropical compacted clayey soil. Seedlings of each species were germinated and monitored in field conditions during 12 months. After this period, 10 plants of each species were excavated to measure shoot versus root data along the soil profile. With the correlated data, we developed a model for each species to estimate root biomass and volume distribution. Results showed that Ricinus became a mature plant in a quarter of time than Moringa, but Moringa had 18% higher survival rate. Root volume distribution of both species was fitted by logistic and exponential models with 90% of their volume within the first 40 cm3 around the tap root. Average lateral root inclination was −22° for Moringa and −36° for Ricinus. Root volume in Moringa was 5.5 times higher than that of Ricinus. The product of stem base by the crown-width for Moringa and stem base by plant-height for Ricinus were the best estimators (R2 > 0.9) for below-ground biomass. We conclude that both species were capable to grow and reproduce in a clayey and compacted soil; nevertheless, Ricinus developed 16% more oblique and sinker roots to maintain its denser crown, while Moringa took advantage of the mass of its dense trunk and roots for a shallower exploration.