Pruning effects on root distribution and nutrient dynamics in an acacia hedgerow planting in northern Kenya

I. Peter et J. Lehmann, Pruning effects on root distribution and nutrient dynamics in an acacia hedgerow planting in northern Kenya, AGROFOR SYS, 50(1), 2000, pp. 59-75
Citations number
Categorie Soggetti
Journal title
ISSN journal
0167-4366 → ACNP
Year of publication
59 - 75
SICI code
Tree pruning is a common management practice in agroforestry for mulching a nd reducing competition between the annual and perennial crop. The below-gr ound effects of pruning, however, are poorly understood. Therefore, nutrien t dynamics and root distribution were assessed in hedgerow plantings of Aca cia saligna (Labill.) H.L. Wendl. after tree pruning. Pruning to a height o f 1.5 m was carried out in March and September 1996. In July and October 19 96, the fine root distribution (< 2 mm) and their carbohydrate contents wer e determined at three distances to the tree row by soil coring. At the same time, foliar nutrient contents were assessed, whereas nutrient leaching wa s measured continuously. The highest root length density (RLD) was always f ound in the topsoil (0-0.15 m) directly under the hedgerow (0-0.25 m distan ce to trees). Pruning diminished the RLD in the acacia plots at all depths and positions. The relative vertical distribution of total roots did not di ffer between trees with or without pruning, but live root abundance in the subsoil was comparatively lower when trees were pruned than without pruning . In the dry season, the proportion of dead roots of pruned acacias was hig her than of unpruned ones, while the fine roots of unpruned trees contained more glucose than those of pruned trees. Pruning effectively reduced root development and may decrease potential below-ground competition with interc ropped plants, but the reduction in subsoil roots also increased the danger of nutrient losses by leaching. Leaching losses of such mobile nutrients a s NO3- were likely to occur especially in the alley between pruned hedgerow s and tended to be higher after pruning. The reduced size of the root syste m of pruned acacias negatively affected their P and Mn nutrition. Pruning a lso reduced the function of the trees as a safety net against the leaching of nutrients for both NO3- and Mn, though not for other studied elements. I f nutrient capture is an important aim of an agroforestry system, the conce pt of alley cropping with pruning should be revised for a more efficient nu trient recycling in the system described here.