168 Tirado-Corbalá and Slater: Soil Compaction Effects on Three Tropical Tree Species The study authors observed a reduction of the ratio at six months after transplanting in both soil types, suggesting in- creasing root support for plants of a given size over time. Leaf dry weight There was a significant effect of soil compaction on leaf dry weight for trumpet bush, but not for bottle brush and pink trumpet. Trum- pet bush species showed greater leaf dry weight under control and intermediate compaction level (Db = 1.2 g/cm3 ) treatment com- pared with high level of compaction (Table 2). The three tree spe- cies had greater leaf dry weight when growing in sandy clay loam compared to trees growing in clay soil (Table 2). The compac- tion and soil type interaction was not significant for any species. Also a reduction in dry weight for trumpet bush and pink trumpet at six months after transplantation was observed, but for bottle brush an increase in leaf dry weight occurred. Figure 5. Root system of pink trumpet [Tabebuia rosea (Bertol.)] harvested six months after planting on three treatments in both soils. The root systems located at left side, represent the trees planted on sandy clay loam, and the root systems located at right side, represent clay soil: (a) control, (b) three layers (Db and (c) seven layers (Db ≈ 1.15 g/cm3 = 1.4 g/cm3 ). Leaf area ), Soil compaction as a main effect showed no signicant difference for leaf area between treatments on the three tree species. Howev- er, the three tree species planted in sandy clay loam soil showed a greater mean foliar area compared to plants growing in sandy clay loam (Table 2). The compaction and soil type interaction was not significant for any species. For all species, there were no signifi- cant differences between the tree species, soil type, or compac- tion, in leaf color. The color remained dark green to green yellow. DISCUSSION Bottle brush and trumpet bush showed significant differ- ence in height as a function of soil density, but there were no differences with pink trumpet. Smith et al. (2001) obtained similar results for Eucalyptus ficifolia, Corymbia macula- ta, and Agonis flexuosa. Small and McCarthy (2002) found Elymus hystrix was not affected by level of compaction. Data from this experiment showed how shoot diameter Figure 6. Visual comparisons of leaf number of trees harvested six months after planting. The visual comparison of leaf number by tree species and soil type. Trees located on left side, were planted in sandy clay loam, and on right side, in clay soil: (a) bottle brush, (b) trumpet bush, and (c) pink trumpet. Leaf Response Leaf number There was a significant effect of compaction on leaf number for trumpet bush, but not for bottle brush and pink trumpet. Trumpet bush species showed greater root dry weight for control and in- termediate compaction level (Db = 1.2 g/cm3 ) treatment compared with high level of compaction (Table 2). The three tree species had greater leaf number when they grew on sandy clay loam com- pared to trees growing in clay soil (Table 2). Bottle brush growing in sandy clay loam soil had twice the number of leaves compared with the same species growing in clay soil (Table 2). The compac- tion and soil type interaction was not significant for any species. Visual results displayed in Figure 6a show bottle brush planted in both soils had a greater leaf number compared with trumpet bush and pink trumpet. The three tree species ex- hibited more leaves in the sandy clay loam soil six month af- ter transplanting (Figure 6a–Figure 6c). However, a reduction of leaf number was found for all three species at six months after transplanting due to coinciding with the dry season. ©2010 International Society of Arboriculture was affected by soil type and level of compaction, especial- ly for the trumpet bush species. Pan and Bassuk (1985) found soil compaction limits growth, shoot diameter, and shoot dry weight. This occurs because of reduction in root growth in limited volumes of soil, reducing the water holding capac- ity. However, other studies emphasize shoot diameter reduc- tion is a combined response to mechanical impedance and an alteration in production of root synthesizer hormones such as gibberellins and cytokines (Krizek and Dubik 1987). The shoot dry weight was affected on all plantings in clay soils at bulk density of 1.4 g/cm3 but was statistically dif- ferent for trumpet bush. A reduction in the shoot dry weight of Eupatorium rugosum planted in high levels of compac- tion was reported by Small and McCarthy (2002) who found, as did Kjelgren and Clark (1993) when Liquidambar styraciflua was planted in small volumes of clay loam soils. Even though there was no significant interaction for soil com- exhibited greater dry root weight compared with the trees planted on clay soil. Grabosky and Bassuk (1996) found that root penetration and root biomass of Quercus robur planted in clay loam soils decreased by 50% at bulk densities higher than 1.4 g/ cm3 . Smith et al. (2001) found a 60% reduction in root growth of Corymbia maculata, Lophostemon confertus, Agonis flexuosa, and Eucalyptus ficifolia in soil compacted a to a bulk density of 1.4 g/cm3 or higher. Costello et al. (1997) found similar results paction level and soil type for root dry weights, the trees planted on sandy clay loam for control treatments and bulk density of 1.2 g/cm3
July 2010
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