Aggregation and soil carbon aggregates distribution in a red latosol under different levels of sugarcane straw in paranavaí (PR)

Abstract

The objective of this work was to evaluate the impact of the application of different levels of sugarcane straw on the aggregation and distribution of organic carbon (C) in aggregate classes of a Red Latosol under mechanical harvest in Paranavaí (PR). For this study, in November 2014, after the mechanical harvesting of cane-plant (variety RB-867515), the following amounts of straw were applied to the soil: 0.00, 3.65, 7.50, and 14.85 Mg ha-1 which corresponded respectively to field maintenance of 0, 25, 50 and 100% of the straw. The experimental design was a randomized block design, with 4 replicates. Approximately one year after application of straw levels on the soil, soil samples were collected in the 0-10 cm layer. In these samples the aggregate mean weight diameters (MWD), the aggregate distribution in the classes of diameters 4-2, 2-1, 1-0.5, 0.5-0.25, and 0.25-0.105 and <0.105 mm by dry route, and the C content in these classes with the exception of class <0.105 mm. In the distribution of the aggregates, there was a predominance of the 0.25-0.105 mm group of aggregates, possibly due to the amount of fine sand (290 g kg-1) present in this sieve diameter, although within this class there was no significant effect of the levels of straw. The higher straw deposition on the soil (50 and 100%) increased the percentage of aggregates in the class 4-2 mm (25.7 and 32.0%, respectively) in relation to treatments 0 and 25% (13.5 and 22.7%, respectively), presenting significant quadratic behavior. The same effect was observed for the MWD values, with higher values in the treatments with 50 and 100% (1.65 and 1.60 mm, respectively) in relation to treatments with 25 and 0% straw (1.32 and 1.01 mm, respectively). Within each straw level, the C contents in the aggregate classes presented significant differences among them, except for the treatment with 100% straw, where in general the values were higher in the classes with diameter of 4-2 and 2-1 mm (12.5 and 12.4 g kg-1, respectively) and lower in the class 0.25-0.105 mm (6.6 g kg-1). Thus, the main conclusions were that the application of 50 and 100% (7.55 and 14.85 Mg ha-1 year-1) increases the aggregation of the soil, and that the application of 50% of straw on the soil also (4-2 and 2-1 mm), which are associated to higher soil organic carbon contents (14.4 and 13.2 g Kg-1, respectively), straw level being more appropriate to keep the surface of the soil to maintain soil structure.