In semi-arid regions, trees often wither during the dry season. Withering is sometimes manifest as die-back, whereby whithering results in shoot death, which progresses downward from the uppermost part of the crown. In this study, we measured the relationships between height growth and diameter at breast height, die-back frequency and severity, vessel size and specific hydraulic conductivity of four evergreen (Senna siamea (Lamk) H.S. Irwin & Barneby, Jacaranda mimosifolia D. Don, Azadirachta indica A.H.L. Juss and Acacia gerrardii Benth.) and one deciduous (Melia volkensii Gürke) plantation tree species in Kenya, which has a conspicuous dry season. Die-back occurred readily in some species, but not in others. Senna siamea showed the highest specific hydraulic conductivity and the highest growth rate among the five species and was quite susceptible to die-back. Among species, height growth and specific hydraulic conductivity were positively correlated with vessel size and negatively correlated with die-back frequency, suggesting a trade-off between growth rate and drought tolerance. This implies that an adaptation to rapid growth under humid conditions leads to low drought tolerance. However, the deciduous tree Melia volkensii showed high specific hydraulic conductivity and growth, with no symptoms of die-back, implying that a mechanism associated with the deciduous habit results in drought avoidance by reducing the requirement for water during the dry season.

No abstract

The study was aimed to examine the effectiveness of Senna siamea leaf comparing with conventional mulches (rice straw and water hyacinth) on growth, yield and water use efficiency (WUE) of common bean and weed infestation at different irrigation levels during the dry season. The experiment was laid out in split-plot design with three replications where three mulches and five irrigations were assigned in main and sub-plot, respectively. Irrigation water (IW)/cumulative pan evaporation (CPE) 1.0, 0.75, 0.50, 0.25 and no irrigation were the five irrigations. Senna leaf mulch maintained favourable soil environment than other mulches. Seed yield of common bean did not vary significantly between Senna leaf (1355.8 kg ha 71 ) and straw (1394.2 kg ha 71 ) mulches, but Senna leaf mulch gave significantly higher yield than water hyacinth mulch (1239.8 kg ha 71 ). No significant variation was recorded in TWU and WUE among mulches. Significantly lower weed infestation was observed in Senna leaf mulch (12.3 g m 72 ) compared to straw (26.6 g m 72 ) and water hyacinth (32.9 g m 72 ). Performance of common bean was better at higher irrigation levels. Results indicate that Senna leaf could be used as an effective mulch to conserve soil moisture and save irrigation water for common bean production.

No abstract

Productivity of maize and soil properties change under alley cropping system consisting of four woody species (Gliricidia sepium, Leucaena leucocephala, Cajanus cajan and Senna siamea) at different nitrogen levels (0, 25, 50, 75 and 100% of recommended rate) were studied in the floodplain ecosystem of Bangladesh. Comparative growth performance of four woody species after pruning showed that L. leucocephala attained the highest height, while C. cajan produced the maximum number of branches. Higher and almost similar amount of pruned materials (PM) were obtained from S. siamea, G. sepium and C. cajan species. In general, maize yield increased with the increase in N level irrespective of added PM. However, 100% N plus PM, 75% N plus PM and 100% N without PM (control) produced similar yields. The grain yield of maize obtained from G. sepium alley was 2.82, 4.13 and 5.81% higher over those of L. leucocephala, C. cajan and S. siamea, respectively. Across the alley, only one row of maize in the vicinity of the woody species was affected significantly. There was an increasing trend in soil properties in terms of organic C, total N and CEC in alley cropping treatments especially in G. sepium and L. leucocephala alleys compared to the initial and control soils. Therefore, one fourth chemical N fertilizer can be saved without significant yield loss in maize production in alley cropping system.