166 Tirado-Corbalá and Slater: Soil Compaction Effects on Three Tropical Tree Species soils, the 18.5 L pots were filled in three lifts. Each lift had a thickness of 12.1 cm and 25 blows were applied to each lift, with a total of 75 blows per pot. To achieve a bulk density value of 1.4 g/cm3 for both soils, the 18.5 L pot was filled in seven lifts. Each layer had a thickness of 5.2 cm and 200 blows were applied to each lift, with a total of 1,400 blows per pot. Soil bulk density was measured using undisturbed samples collected from the pots using the clod method (Brasher et al. 1966; Blake and Hartge 1986) (Table 1). RESULTS Figure 2. (a) Experimental pot with PVC pipe inside the metallic mesh, ( b) the experimental pot without the PVC pipe, and (c) after the tree was transplanted in the experimental pot, same soil type was used to fill out the empty space inside the metallic pot. Seedling Planting Seedlings of same height (47 cm) for three species were potted in the inner pot created with metallic mesh. The empty space in the metallic mesh pot was filled with the same soil type but not com- pacted. Seedlings were placed randomly into the growing area with a spacing of 30 cm x 60 cm. The experiment lasted six months (August 2003–February 2004), during which time the trees re- ceived only natural rainfall and full sunlight. Every two months, 36 trees (two replicates per species-soil-compaction-treatment) were harvested. The following morphological variables were measured: tree height, shoot diameter, leaf number, foliar area, leaf, shoot, and root dry weights, and leaf color (determined us- ing a Munsell Chart, Kollmorgen Instruments Corporation 1977). Statistical Analysis For each species, bulk density combination, and soil type, six pots were established. Every two months, 36 trees (two replicates per species-soil-compaction-treatment) were harvested. The data were analyzed using analysis of variance procedure PROC MIXED within SAS v.9.1.3 (SAS Institute Inc., Cary, NC). Soil and treat- ments were considered fixed effects and time and replicates were considered random effects. Means were separated using (Tukey test) mean separation test at the alpha < 0.05 level of significance. Table 1. Bulk density of two soils under different levels of compaction using clod method. Soil Sandy clay loam Clay z Compaction level Control Intermediate High Control Intermediate High Bulk density (g/cm3 1.07±0.25 1.20±0.01 1.40±0.02 1.05±0.01 1.22±0.26 1.42±0.02 Means and standard errors are listed to indicate soil compaction level and soil type variability. )z Tree Height Bottle brush grew rapidly during the first four months (from 47 cm to 116 cm) but thereafter grew slowly, achieving a final height of 126 cm. Trumpet bush and pink trumpet grew rapidly during the first two months (an increase in height of 91 cm and 84 cm, respectively), but thereafter grew slowly, achieving final heights of 96 cm and 83 cm, respectively. There was a signifi- cant effect of compaction for bottle brush and trumpet bush, but not for pink trumpet (Table 2). Bottle brush was taller at high and intermediate levels of compaction compared with control. Trumpet bush, had greater height under control treatment which represent looser soils (Figure 3). Also, trumpet brush has great- er height under sandy clay loam soils compared with clay soils (Table 1). There was a signicant effect of soil type for trumpet bush but not for bottle brush or pink trumpet. Trumpet bush was taller for sandy clay soils compared with clay soils. The compac- tion and soil type interaction was not significant for any species. Figure 3. Root system of trumpet bush [Tecoma stans (L.)] har- vested six month after planting on three compaction levels in both soils. The root systems located at left side, represent the trees planted on sandy clay loam, and the root systems located at the right side, represent clay soil: (a) control, (b) three layers (Db ≈ 1.15 g/cm3 ), and (c) seven layers (Db Shoot Response Shoot diameter There was a significant effect of compaction for trumpet bush, but not for bottle brush and pink trumpet tree species (Table 2), on shoot diameter. Trumpet bush had greater shoot diam- eter at control (6 cm) and intermediate level of compaction (Db = 1.2 g/cm3 fect of soil type for trumpet bush and bottle brush trees plant- ed in sandy clay soil compared with clay soils (Table 2). Soil type was not significant for pink trumpet. The compaction and soil type interaction was not significant for any species. paction (Db = 1.4 g/cm3 Shoot dry weight 1.4 g/cm3) (Table 2). There was a significant effect of soil type ) compared with high level of compaction (Db There was a significant effect of compaction for trumpet bush, but not bottle brush and pink trumpet tree species (Table 2), on shoot dry weight. Trumpet bush trees growing in control and intermediate level of compaction had greater shoot dry weight (Db = 1.2 g/cm3 = for trumpet bush, but not for bottle brush and pink trumpet tree species. Trumpet bush had greater shoot dry weight when growing in sandy clay loam, almost twice the dry weight com- ©2010 International Society of Arboriculture = 1.4 g/cm3 ). ) (4.8 cm) compared with high level of com- ) (1.9 cm). There was a significant ef-
July 2010
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