Carbono e macroagregados do solo como indicador de qualidade em áreas sob diferentes manejos de cultivo de cana-de-açúcar

Abstract

Zona da Mata of Pernambuco has an extensive area under long-term sugarcane monoculture under management systems such as minimal and conventional crops that cause different effects on the chemical, physical and biological quality of the soil. Soil macroaggregates stand out as indicators of soil physical quality, as they are sensitive to management, reflect the sustainability of the management adopted in the area, are structures that protect organic carbon (C), preventing further oxidation by microbial activity. The objective of this study was to evaluate the soil quality in relation to the variation of carbon and soil macroaggregates under different sugarcane cultivation managements, compared to native vegetation (Atlantic Forest). Fifteen trenches were sampled at random, in paired areas with the same soil order (Red-Yellow Latosol) and texture, where five were in a sugarcane area with minimum cultivation (CM), five in an area of sugarcane. sugar under conventional cultivation (CC) and five in an area of native vegetation (VN). Deformed and undisturbed soil samples were collected at depths 0-5, 5-10 and 10-20 cm. In the laboratory, the wet sieving of samples in duplicates was carried out to observe the stability of aggregates in water and separation of the classes of aggregates into Microaggregates (0.053-0.25 mm), small (0.25 - 2 mm) and large Macroaggregates (2 – 8 mm). The C analysis was performed via wet combustion in order to calculate the TOC and total carbon stock as well as the C stock of the aggregate classes. In each class of households in the different managements adopted, the following were calculated: Distribution (proportional weight) of households; stock C; Mean Weighted Diameter (MWD); Mean Geometric Diameter (MGD); Aggregate Stability Index (ASI); and Loss rate of C. The MDG showed results varying between the three areas studied from 4.22 to 4.89 for layer 0-5 cm, 3.80 to 4.89 for layer 5-10 cm and 3.10 at 4.72 to 10-20 cm; the MGD was the same for all areas and depths (0.98); and the ASI was elevated for the three areas and at all depths, ranging from 97.6 to 99.7%. The soil density was higher for the CT area (1.47 g cm-3) and lower for the NV area (1.24 g cm-3). Sugarcane monoculture under CT and MT increased soil density when compared to NV by 20.7 and 13.2%, respectively. The large macro-aggregates had a distribution (proportional weight) of 95% for NV, 83% for MT and 67% for CT. However, the small macro-aggregates showed a distribution of 31% for CT, 15% for MT and 4% for NV. The average carbon stock in the large macroaggregates followed the following decreasing order NV> MT> CT, being 74.4 Mg ha-1; 57.78 Mg ha-1 and 52.85 Mg ha-1, respectively for the 0-20 cm deep layer. The small macroaggregates obeyed the following decreasing order CT> MT> NV, being 23.16 Mg ha-1; 10.10 Mg ha-1 and 2.34 Mg ha-1, respectively for the same layer. The rate of loss of C in the layer 0-20 cm deep showed that the areas of MT and CT decreased the structural quality of the soil by 22.3 and 28.9%, respectively. The soil structural quality of the soil macroaggregates followed the following decreasing order: NV> MT> CT at the time of the management used in the areas. The class of large macroaggregates (2-8 mm) was sensitive to differentiate the management of MT and CT.