Chemical Properties of an Oxisol with Differents Uses in Western Amazonia.

The replacement of native Amazon forest to agricultural land often depletes soil carbon and fertility. However, soils managed by indigenous peoples, thousands of years ago, resulted in highly fertile Terra Preta and Terra Mulata soils. This study aimed to evaluate chemical properties of an Oxisol that is in native forest with land that was converted from native forest to orange orchards, and pasture approximately 15 years ago. Comparisons were also made with nearby Terra Preta and Terra Mulata soils converted to orange production, at the same time. The soil types and production practices are, typical of Manacapuru – AM - Brazil. From each site, an auger was used to collect 15 subsamples to form a composite sample, at 0-5, 5-10 and 10-20 cm depths. Soil pH(CaCl₂) was low in the Terra Preta soil but high in the Oxisol soil under cultivation or grazing. The Terra Preta soil contained greater amounts of total recoverable Ca, Mg, K, P, Mn and Zn, compared with the other sample sites. Total Kjehldahl N and total recoverable B showed little difference among sites. After 15 years of orange production, Terra Preta and Terra Mulata soils maintained their fertility, whereas the Oxisol soils under cultivation have depleted fertility.