Observations of Some Tree Root Systems in Agroforestry Intercrop Situations, and their Graphical Representation

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Abstract
Summary: Root systems of unprunedCassia siameaandLeucaena leucocephalatrees and regularly pruned hedges ofC. siamea, L. leucocephalaandGliricidia sepiumwere examined in a semi-arid area in Kenya. Trenches were dug across rows of trees or hedges, soil profiles washed, and different sized roots counted in small 5 × 5 cm grids fully covering both faces of the trench. The roots were displayed using two computer software programmes written for this purpose: a spline technique that displays smoothed root densities in different shades; and a random dot method which displays roots as dots, using any specified scale. The fine roots of four-and-a-half-year-oldC. siameapenetrated the soil to meet with rocks at depths between 0.60 and 2.0 m, and spread laterally to 9 m, traversing adjacent crop plots. Roots of eight-year-oldL. leucocephalacovered an extensive soil volume and included a greater density of fine roots thanC. siameaat comparable distances. Above-ground pruning restricted the roots of hedges to a depth of 1.5 m, although roots of different hedges spaced 5 m apart intermingled freely in the alley space.L. leucocephalaroots filled the alley very densely while those ofG. sepiumwere sparse, particularly in the middle of the alley. Rooting density ofC. siameawas intermediate. The dot method is more precise when rooting densities are low but when densities are high the splining method appears to be more visually helpful. These graphical methods greatly facilitate overall comparisons of sections of tree root systems, but quantification of root densities at different distances away from trees is still needed to understand more precisely the competitive effects of trees and associated crops.Systemas de raices de los árboles