Banca de DEFESA: JULIO CESAR CALIXTO COSTA

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : JULIO CESAR CALIXTO COSTA
DATE: 31/07/2025
TIME: 09:00
LOCAL: UFRPE
TITLE:

Rotation of Brachiaria Grass and Sugarcane in Sandy Soil: Impacts on Aggregation and Carbon Fractions

KEY WORDS:

Conservation practices; Seeding densities; Saccharum officinarum L.; Brachiaria ruziziensis

PAGES: 73
BIG AREA: Ciências Agrárias
AREA: Agronomia
SUBÁREA: Ciência do Solo
SPECIALTY: Manejo e Conservação do Solo
SUMMARY:

Brazil is the world's largest producer of sugarcane, playing a significant role in both biofuel and food production, with a notable impact on the socioeconomic landscape. Although the main production hub is the Center-South region, northeastern states such as Alagoas, Pernambuco, and Paraíba also stand out. The expansion of monoculture has intensified soil-related problems, especially in sandy soils characterized by low organic matter, low water retention, and high permeability. In this context, the use of organic material through conservation practices – such as crop rotation systems, particularly with grasses from the Brachiaria genus – is recommended due to their good adaptability, nutrient cycling potential, and high biomass production. Thus, it is essential to investigate such systems in sandy soils, with emphasis on different sowing densities of Brachiaria grass, to optimize management and promote agricultural sustainability by selecting more appropriate seeding rates. Given this, the objective was to evaluate the effect of Brachiaria sowing densities in rotation with sugarcane on soil aggregation and organic carbon fractions. The study was conducted at Usina Giasa, located in Pedras de Fogo, Paraíba, using a randomized block design in split plots with four replications. The main plots were composed of Brachiaria sowing densities: 0, 10, 30, and 50 kg ha-1 of seeds. Subplots were defined by sampling depths: 0-10, 10-20, and 20-40 cm. Both undisturbed blocks and disturbed soil samples were collected. A physicochemical characterization of the experimental area was carried out. The contents and stocks of total organic carbon (TOC), particulate organic carbon (POC), and mineral-associated organic carbon (MAOC) were evaluated, along with the distribution of macroaggregates by size class using wet sieving. Data were subjected to analysis of variance using the SISVAR software, applying the F-test and, when significant at 5%, Tukey’s test for mean comparisons. No significant differences were found for bulk density, particle density, or total porosity. Carbon contents and stocks were analyzed individually to assess the effect of sowing density. The TOC and POC fractions were not statistically significant; however, stocks in layer P3 were higher at the D10 density. Regardless of treatment, MAOC represented the largest proportion of soil C, ranging from 88.51% (D30) to 90.73% (D10). Sowing density influenced both the geometric and weighted mean diameter of aggregates, while depth affected the aggregate stability index. For the extra-large macroaggregate class, only the 10-20 cm layer showed an effect of sowing density on the mean proportion of aggregates (MPA), with D30 accounting for 56% of macroaggregates. A predominance of large macroaggregates in the 0-10 cm depth was observed at D10, and no significant differences were found for small macroaggregates. Overall, across all macroaggregate size classes and depths, the highest TOC and POC stocks were associated with the 10 and 30 kg ha-1 Brachiaria sowing densities. Therefore, sowing densities of 10 and 30 kg ha-1 increased both the content (P1) and the stock (P3) of soil organic carbon fractions. The rotation between Brachiaria grass and sugarcane positively impacts soil aggregation and carbon accumulation under sandy conditions in the short term. Sowing densities between 10 and 30 kg ha-1 are recommended for use in rotational systems due to their superior performance across most of the evaluated variables

COMMITTEE MEMBERS:
Presidente - ADEMIR DE OLIVEIRA FERREIRA
Interno - ***.340.804-** - WILLIAM RAMOS DA SILVA - UFRPE
Externo à Instituição - CLEVER BRIEDIS - UFV