Abstract
Fertility properties, total C (Ctot), and chemical soil organic matter fractions (fulvic acid fraction - FA, humic acid fraction - HA, humin fraction - H) of anthropogenic dark earths (Terra Preta de Índio) of the Amazon basin were compared with those of Ferralsols with no anthropogenic A horizon. Terra Preta soils had a higher fertility (pH: 5.1-5.4; Sum of bases, SB: 8.93-10.33 cmol c kg-1 , CEC: 17.2-17.5 cmol c kg-1 , V: 51-59 %, P: 116-291 mg kg-1) and Ctot (44.6-44.7 g kg-1) than adjacent Ferralsols (pH: 4.4; SB: 2.04 cmol c kg-1, CEC: 9.5 cmol c kg-1, V: 21 %, P 5 mg kg-1, C: 37.9 g kg-1). The C distribution among humic substance fractions (FA, HA, H) in Terra Preta soils was also different, as shown by the ratios HA:FA and EA/H (EA=HA+FA) (2.1-3.0 and 1.06-1.08 for Terra Preta and 1.2 and 0.72 for Ferralsols, respectively). While the cation exchange capacity (CEC), of Ferralsols correlated with FA (r = 0.97), the CEC of Terra Preta correlated with H (r = 0.82). The correlation of the fertility of Terra Preta with the highly stable soil organic matter fraction (H) is highly significant for the development of sustainable soil fertility management models in tropical ecosystems.
Highlights
The role of organic matter (SOM) in soil fertility has long been known
This fact is a possible explanation for the better fertility characteristics (Table 2) of the dark earths compared to non-anthropogenic soils
There was no significant difference between cultivated anthropogenic soils (ASC) and those under forest (ASF), except for available P that was higher for ASC
Summary
The role of organic matter (SOM) in soil fertility has long been known. In humid and hot tropical environments, soils, due to the pronounced weathering process resulting in an intense removal of silica and bases by lixiviation, are acid, and have low natural fertility (Soares et al, 2005). This restriction, does not reduce the biodiversity and development of exuberant vegetation as in the case of the Amazon Forest. Litter deposition on the soil surface is high (8-10 Mg ha-1 yr-1) and the flux and turnover of nutrients intensive (Villela & Proctor, 1999). The SOM plays an important role in environmental protection
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