Monday, November 5, 2007
119-27
Effects of Charcoal and Organic Fertilizer on Phosporus Adsorption and Bioavailability in Soils of the Central Amazon.
Terra Preta do Indio (Dark Earth Soils) are a long-term source of soil phosphorus for agriculture and forest productivity in the Central Amazon. One reason given for these soils’ high phosphorus bioavailability has been the presence and chemical characteristics of soil charcoal, which is a relic from their occupation by Amerindians over periods of 100’s to >2,000 years. Recent studies have confirmed positive chemical benefits derived from the presence of charcoal. The two objectives of this series of studies were to (1) investigate the P adsorptive capacity and the nutrient bioavailability of charcoal made from different sources of wood and with a range of carbonization temperatures; (2) determine the effect of charcoal in remediation of degraded soils under both greenhouse and field environments. Phosphorus sorption isotherms were developed for all charcoal sources. Carbonization temperature had no influence on P sorption for charcoal made from the tree species, Lacre and Íngá; while the tree species, Imbaúba, produced charcoal of lower P sorption ability at 400 0C than at temperatures 600 0C and above. Phosphorus sorption onto recently made charcoal was within the same range as P sorption onto charcoal removed from Terra Preta, even though the particle sizes were different (<2mm for new charcoal versus >2mm for Terra Preta charcoal). When charcoal was added to soil in a greenhouse environment, seedlings of the tropical tree species, Enterolobium cyclocarpum, did not exhibit a growth response. However, the soil increased in exchangeable K, decreased in exchangeable Al and greatly increased in pH. When charcoal, along with rock phosphate, was used in the planting hole of a degraded soil cleared for oil exploration, the P levels in the leaves of Vismia guianensis (Lacre) were unaffected by the presence of rock phosphate. Charcoal has a high capacity to sorb and change the amount of exchangeable cations, including reducing the potential toxicity of Al in these low pH soils by increased Al adsorption and increasing soil pH. However, there was no growth benefit from the charcoal in either a greenhouse environment or a highly degraded soil environment. The latter was complicated by a high level of compaction, which also influenced the results. These data add to the evolving information on charcoal properties and its influence of soil-plant interactions. While, previous studies have indicated the positive benefits of charcoal for plant growth, the plant species employed and other soil properties may limit that effect.
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