ROOT DISTRIBUTION OF DACTYLADENIA (ACIOA) BARTERI AND SENNA (CASSIA) SIAMEA IN ALLEY CROPPING ON ULTISOL .1. IMPLICATION FOR FIELD EXPERIMENTATION

Root observations were carried out on a typic Paleudult in the humid f orest zone of south eastern Nigeria in an alley cropping trial using D actyladenia (Acioa) barteri and Senna (Cassia) siamea as hedgerow tree s and the interrow space planted to maize/cassava intercrop. Rooting d epth of D. barteri and S. siamea exceeded 1.6 m. Lateral root propagat ion of S. siamea was 15 m, and of D. barteri was 5 m from the hedgerow s. The whole no-tree control plot was within the range of roots of the adjacent hedgerows. Rooting density and depth of S. siamea in the no- tree control plot was generally higher than of cassava. S. siamea and cassava root density were inversely correlated. Assuming radial symmet ry of root propagation, water and nutrients were available from an are a 6.1 and 2.3 times larger than the allocated plot size of S. siamea a nd D. barteri, respectively. Data obtained in alley cropping trials, n ot considering lateral root propagation, can be invalidated through ex ploitation of the no-tree control treatment and nutrient acquisition b y hedgerow species from a larger area than allocated, thus underestima ting and overestimating the performances of the respective treatments. Possible alternative measures for avoiding root interference are disc ussed but no good solution can be given.