Carbono do solo oxidável por permanganato de potássio em plantios de dendezeiro em sistemas agroflorestais e monocultivo

Abstract

For oil palm production, cultivation in agroforestry systems is considered a sustainable alternative to the conventional (monoculture) system, as it combines adequate bunches production with the provision of environmental services, such as maintaining soil quality. Soil quality can be indicated, among other ways, by quantifying fractions of soil organic matter, among which is the fraction oxidized by potassium permanganate. The objective was to evaluate the content of carbon oxidized by KMnO4 (C-POX) in agroforestry systems with oil palm, comparing them to the monoculture system and a successional forest, in order to verify the soil quality of these ecosystems. The experiment was conducted in the municipality of Tomé-Açu, Pará, in three demonstrative units (UD1, UD2 and UD3) of the SAF-Dendê Project. Each UD has two agroforestry systems whose main species is oil palm, one with a predominance of fruit and timber species, called SAF-Biodiverso (SAF-B), and the other with a higher frequency of fertilizer plants, called SAF-Adubadeira (SAF- A), which are arranged in such a way as to merge a double line of oil palm and diversified bands (StripSAF). For comparison with the conventional oil palm production system, two monocultures were selected: MON1, which was compared with UD1 and UD2, and MON2, used as a reference for UD3. The agroforestry systems of the three UDs were compared to successional forests (FLO1, FLO2 and FLO3) adjacent to each demonstrative unit. Five plots were established at random in each system. Soil samples from the 0-10 cm layer were collected at specific locations within each plot (management zones): harvest path (CAR), weeded circle (BAS), frond pile (PIL) and Zone-SAF. The content of oxidizable carbon by KMnO4 (C-POX) was determined. Comparing the land use systems of UD1 and UD3, the SAF-A s had a higher C-POX content (1063 and 812 mg kg-1 soil, respectively) than the other systems in these UDs. In UD2, the highest content occurred in SAF-B, 1048.64 mg kg-1 soil, compared to the other systems. There was no significant effect of the interaction between oil palm production systems and management zones that are influenced by oil palm (CAR, BAS and PIL); however, in general, in all UDs, SAFs with oil palm had a C-POX 9 content 40% higher than conventional production systems. For the management zones factor, the results obtained showed that the frond pile has a higher C-POX content than the others. The frond pile and the Zone-SAF in the three UDs were significantly higher than the CAR and BAS. Therefore, it is concluded that the labile oxidizable carbon by KMnO4 is sensitive to changes in the management of the systems, allowing to indicate that agroforestry systems with oil palm presented better soil quality than the monoculture oil palm. The difference in the spatial distribution of C-POX in SAFs and monoculture is consistent with the role of organic matter management in improving soil quality.