Note: Program subject to change without notice

Monday, November 5, 2007
92-6

Exchangeable and Organically Bound Al3+ in Alonso Soil Treated with Leaf Litter Material.

Miguel Munoz, Emmanuel Feliciano, and Katherine Quinones. University of Puerto Rico, College of Agricultural Sciences, PO Box 9032, Mayaguez, PR 00680

Coffea arabica and Pithecellobium carbonarium leaf litter was added to Alonso soil (Oxic Dystrudepts) to asses the effect on extractable Al3+. Four leaf litter treatments were evaluated: 1) No leaf litter (Check); 2) three percent Coffea arabica leaf litter; 3) three percent Pithecellobium carbonarium leaf litter; and 4) three percent of a 1:1 Coffea Arabica:Pithecellobium carbonarium leaf litter mixture. Six grams of leaf litter were mixed with 200 g of soil collected at 0-20 and 20-40 cm depths. The soil was moist with 60 ml of distilled water, placed on glass jars and incubated at room temperature. Each treatment was replicated four times and arranged in a complete randomized block design. Exchangeable Al3+ was extracted with 1 NKCl , extractable Al3+ weakly bound to soil organic matter was extracted with 0.33 M LaCl3 and extractable Al3+ strongly bound to soil organic matter was extracted 0.5 M CuCl2. The highest soil exchangeable Al3+ , 1.43 cmolc kg-1, was observed on the check treatment, followed by the Pithecellobium leaf litter with 1.29 cmolc kg-1, the 1:1 mixture with 0.59 cmolc kg-1 and the coffee leaf litter with 0.31 cmolc kg-1. Significantly larger amounts of Al3+ were extracted with 0.33 M LaCl3 and 0.5 M CuCl2 than with 1 N KCl, a clear indication of the importance of organic matter in Al3+ complexation reactions. The highest pH (4.29) was observed on coffee litter treated samples, the check showed a pH of 4.00, the 1:1 leaf litter showed a pH of 3.94 and the Pithecellobium leaf litter showed a pH of 3.90. The significant decrease in exchangeable Al3+ with the addition of Coffea and Pithecellobium leaf litter, even in cases where a decrease in soil pH was observed, indicates that other mechanisms, besides pH, are involved in the neutralization of extractable Al3+fractions.