A field experiment was established on Alonso soil (Oxic Dystrudept) to evaluate soil extractable aluminum. Plots included full sunlight coffee, high density shade coffee, and low density shade coffee. Soil samples were collected at 0-20 and 20-40 cm depths. Soil pH at 0-20 cm was 5.12 for full sunlight, 4.47 for high density shade, and 4.83 for low density shade. At 20-40 cm depth soil pH was 4.64, 4.57, and 4.66, for the same treatments, respectively. Organic matter content at 0-20 cm depth was 2.77 at full sunlight, 2.89 at high density shade, and 3.58 at low density shade. At 20-40 cm depth was 2.02, 2.04, and 2.63, respectively. Four Al3+ extractants were evaluated: 0.2M NH4Cl, 1M KCl, 0.33M LaCl3, and 0.5M CuCl2. In the full sunlight plot, at 0-20 cm depth, 0.2M NH4Cl extracted 5.97 cmolc kg-1 of Al3+, 1M KCl extracted 7.60 cmolc kg-1, 0.33M LaCl3 extracted 7.22 cmolc kg-1 and 0.5M CuCl2 extracted 9.33 cmolc kg-1. In the high density shade, extractable Al3+ were 6.47 cmolc kg-1, 7.99 cmolc kg-1, 8.18 cmolc kg-1, and 9.96 cmolc kg-1, for the same treatments, respectively. Extractable Al3+ in the low density shade was significantly lower than in the other plots. The 0.2M NH4Cl solution extracted 1.82 cmolc kg-1, 1M KCl extracted 2.52 cmolc kg-1, 0.33M LaCl3 extracted 2.28 cmolc kg-1, and 0.5M CuCl2 extracted 6.73 cmolc kg-1. Extractable Al3+ at 20-40 cm showed higher values with all extractants. Lower amounts of Al3+ were extracted from the low shade density plot, which contained the higher organic matter content.
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