Root length dynamics in agroforestry with Gliricidia sepium as compared to sole cropping in the semi-deciduous rainforest zone of West Africa

Abstract

Tree root systems may improve soil fertility through carbon inputs, uptake of leachable nutrients and maintenance of soil biomass, but can at the same time reduce crop yields by competition for water and nutrients. Quantitative information about the positive and negative effects of tree roots and their changes in space and time are necessary for the optimization of agroforestry associations. An alley cropping experiment was layed out as a randomized complete block design on a Plinthic Lixisol/Ferralic Cambisol with Gliricidia sepium hedgerows at 5 m distance, including a sole cropping control. The development of root systems was monitored by sequential soil coring (eight samplings) during one year, with maize and groundnut as crops. Additional information is presented from a single sampling for rice during the foregoing year. Pronounced fluctuations of live root length density indicated an important variability in the nutrient and water uptake capacity of the vegetation. At low total root length density, the hedgerows affected the root development in the agroforestry plots directly by the presence of their root systems. At high root length density, they affected root development mainly by improving crop root growth and influencing the composition of the spontaneous vegetation. The root length density of the hedgerows was too low to compete with the crops for soil resources. The hedgerows tended to increase root length densities in the subsoil when few roots were present, thus possibly reducing the risk of nutrient leaching. However, the length density of the perennial root systems decreased during the cropping season, presumably as an effect of repeated pruning, and attained minimum values almost at the same time as the crops. Trees with denser root systems which are less frequently pruned may be more efficient in achieving closer nutrient cycles, though at the cost of higher root competition with crops.

Nitrogen dynamics in maize-based agroforestry systems as affected by landscape position in southern Malawi

“…On the other hand studies at Makoka in Malawi observed that gliricidia has very deep rooting systems (>3 m), with < 15% at the top 0-20 cm soil and 79% to 63% of the roots below the effective rooting zone of maize (0-30 cm depth), indicating a differential rooting pattern between trees and crops and low potential for competition. A similar study in Cô te d'Ivoire had also suggested that gliricidia have few surficial roots and minimally compete with associated crops (Schroth and Zech 1995). These studies confirmed that gliricidia rooting patterns are different from those of maize.…”

Effect of pruning on Prosopis juliflora: considerations for tropical dryland agroforestry

“…Less depletion of soil water in the crop rooting zone associated with reduction in root length density in pruned plots of P. juliflora in a semi-arid region of north-east Nigeria has been previously reported ( Jones et al, 1998). A reduction of root density following pruning has also been found in A. saligna (Peter & Lehmann, 2000), Sesbania sesban and L. leucocephala (Fownes & Andersson, 1991), and G. sepium (Schroth & Zech, 1995). Many more species maintain a balanced shoot-to-root ratio and grow a large number of superficial roots when pruned, including Cassia siamea and Calliandra calothyrsus Meissn.…”

Detection of nitrogen transfer from N2-fixing shade trees to cacao saplings in 15N labelled soil: ecological and experimental considerations

“…In the nature, the latter may occur if the rhizospheres of the two species overlap. Given the very high fine root density of both trees and crops in some agroforestry systems (Dossa et al 2008;Muñoz and Beer 2001;Schroth and Zech 1995) overlap of rhizospheres and, consequently, N transfer via the exudate pathway is likely. The formation of CMN may require that both plant species form symbiosis with the same fungal species because anastomoses, functional connections between hyphae, mostly occur between fungi of same species (Giovannetti et al 2006).…”