186 Ferrini et al.: Effect of Fertilization and Backfill Amendment on Oak larger than 500 mm. Pores larger than 500 mm are impor- tant for soil aeration and drainage (especially in heavy textured soils) and for root penetration. The same behavior was observed at 30 to 40 cm (12 to 16 in.) depth (data not shown). Macroporosity measurements of the control soil showed the presence of low porosity values for all pores type and size classes both at 10 to 20 and 30 to 40 cm (4 to 8 and 12 to 16 in.) depths. Fertilized soil exhibited a pore size distribution similar to the control, except for an higher quantity of wide (>1000 mm), irregular pores at 10 to 20 cm (4 to 8 in.) depth (Figure 2). However, microscopic observation of soil thin sections (Figure 3c) revealed a poor continuity of these type of pores. The thin sections of the control (Figure 3d) confirmed the presence of a rather massive soil structure, while micromorphological examina- tion of thin sections of soil amended with compost (Figure 3a) showed a well-defined subangular blocky structure and the presence of vertically oriented elongated pores. Soil amended with leonardite evidenced very large elongated pores (fissures), positively affecting downward water movement. An overall insight of the soil pore system show a rather low intra-aggregate porosity (Figure 3b), indicating that this type of amendment is less effective than compost in terms of structuring capability. Figure 1. Effect of treatments on cone resis- tance. In each soil layer (0 to 15, 15 to 30, 30 to 45, and 45 to 60 cm [0 to 6, 6 to 12, 12 to 18, and 18 to 24 in.]), mean values differ signifi- cantly when followed by different letters at P ≤ 0.05 (LSD test). microorganisms; the transmission pores (elongated and continuous pores), ranging from 50 to 500 mm, are particularly important in soil–water–plant relationships. Damage to soil structure can be recognized by a decrease in the proportion of transmission pores (Pellegrini et al. 2000). Figure 2 shows pore shape and size distribution for different treatments at 10 to 20 cm (4 to 8 in.) depth. The soil treated with compost and leonardite showed a very high proportion of elongated transmission pores, especially those CONCLUSIONS The initial period after planting is the most critical for success and is decisive for the tree’s survival. However, it is widely believed that trees, after the initial shock, recover in the following years, once root system functions have been restored. This may happen, but frequently the opposite occurs: trunk and root growth remain closely correlated to that of the previous year. Some trees die after 4 to 5 years of stunted growth; others, after the same period of time, are able to recover, but in the meantime their aesthetic value is reduced and they end up being smaller than their predicted size. The results of the present study point out that, whenever adequate water is ensured, the most important factor for trees is fertilization. Above all, in the second and third years, tree fertilization was a determinant for greater photosynthesis, total chlorophyll, and leaf area values when compared with the Table 5. Effect of treatments on different pore types and total macroporosity of the 10 to 20 and 30 to 40 cm (4 to 8 and 12 to 16 in.) layers, expressed as a percentage of area occupied by pores larger than 50 mm per thin section. Porosity values differ significantly when followed by different letters at P ≤ 0.05 (LSD test). Regular pores Leonardite 1.94 ns* 2.60 ns 2.01 Fertilization 1.35 Control 1.54 1.88 1.49 2.06 ©2005 International Society of Arboriculture Irregular pores 3.56 ns 4.76 3.06 2.22 3.80 ns 3.42 2.17 2.82 Elongated pores 5.76 ab 7.62 a 1.50 b 0.73 b 5.41 ab 10.14 a 1.98 b 1.44 b Total porosity Treatment 10–20 cm 30–40 cm 10–20 cm 30–40 cm 10–20 cm 30–40 cm 10–20 cm 30–40 cm Compost 11.27 a 14.39 a 5.92 b 4.50 b *Values differ significantly when followed by different letters at P ≤ 0.05 (LSD test); ns = not significant. 11.82 a 15.44 a 5.64 b 6.32 b
July 2005
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