Evaluation of the effect of Gliricidia sepium (Steud) Jacq mulch and leaves harvesting on the growth and yield of Xanthosoma sagittifolium (L) Schott.

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Three experiments were conducted at the Institute of Renewable Natural Resources (IRNR) farm, University of Science and Technology (UST), Kumasi-Ghana from April, 1998 to March, 1999 with the following objectives: To evaluate the effect of Gliricidia sepium mulch and cocoyam leaves harvesting on: a) the establishment, growth and yield of Xanthosoma sagittifolium (L) Schott. b) soil properties, and c) the most economic alternative for Xanthosoma sagittifolium production. A factorial design was employed in Experiment I with main plot treatments (fertilizer) at three levels and subplot treatments (mulch) at two levels with four replicates. A randomized complete block design was used to test treatments in the second and third experiments which were replicated four and three times respectively. Soil samples (0-15cm depth) were collected both before and after planting and analysed for their chemical and physical properties. Soil moisture content and soil temperatures were measured at 4 to 5 weeks after planting (WAP) using gravimetric method and soil thermometer. Counting and measuring of plant parts were done at 2-4 weeks interval, yield parameters were recorded in each treatment at 21 WAP for all experiments and at 44, 41 and 38 WAP for Experiments I, II and III respectively. The results indicated that Gliricidia mulch had a significant effect on the establishment, growth, development, suckers formation, leaf size, tuber formation and cormel weight. A highly significant effect (p = 0.01) was observed on soil moisture content, soil temperature and weed control but not on soil chemical properties. Mulch alone (F0M1) at 20 t/ha increased yield by 245%; 2.14 tons of cormel/ha for F0M0 to 5.21 tons/ha for F0M1 The same amount was obtained by applying inorganic fertilizer at 75 kgN/ha without mulch (F1/2M0). The mulch treatment showed superiority over fertilizer treatment in terms of economic viability. However, highest cormel yield were realized in mulch/fertilizer combination only within a certain range (20 t/ha mulch and 75 kgN/ha). Further increase in inorganic fertilizer to 150 kgN/ha reduced yield by 12.3%. Results indicated that highest root mass and plant suckers were realized in fertilizer treatments. Increasing mulch alone from 10 to 25 tons/ha mulch increased cormel yield by 248% (p = 0.05). Yield of cormel was significantly reduced by leaves harvesting. At the highest inputs level (150 kgN/ha + 25 tons/ha mulch) yield tended to decline with severity of defoliation (LALL < L4 > L3 > L2). However, total yield (leaves and cormel) were highest on intensively harvested plots (L2 > > > LALL) and thus recorded the highest Benefit-Cost-Ratio. Analysis of Benefit-Cost Ratio favoured lower supplementation of inorganic fertilizer with mulch (75 kgN/ha combined with 20 tons/ha mulch) It would be necessary to conduct this experiment for more than one season, because some of production cost in the first season would be cancelled in the subsequent seasons. Bumper harvest of corm (setts) was not assigned value in the economic analysis. Further study in the area of slash-and-mulch or cut-and - carry (biomass transfer) using slow decomposing pruning’s from the multipurpose trees is important and beneficial.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the award of the Degree of Master of Science in Agroforestry, 1999