Sistemas de integração pecuária-floresta: influência de espécies forrageiras e do espaçamento sobre carbono orgânico nos agregados de um cambissolo no semiárido do Ceará.

Abstract

In the Brazilian semi-arid region, traditional systems of agriculture and livestock farming prevail. These changes in land use contribute to soil degradation, causing the destruction of soil aggregates, exposing organic matter, and resulting in the loss of soil carbon. With this, nature- based solutions are being studied and implemented with the aim of promoting more sustainable agriculture. An example is integrated production systems, a model that has provided sustainability in agriculture and increased productivity, in addition to minimizing GHG emissions. In this sense, the objective of this study was to evaluate the effects of adopting Integrated Livestock-Forest Systems (ILF) in the Brazilian semi-arid region through the physical structuring of the soil at different spacings and depths, with the implementation of different crops, using native vegetation (Caatinga) as a reference. The study was conducted at the Teaching, Research, and Extension Unit of IFCE in Ceará, Limoeiro do Norte Campus. The evaluated systems consisted of six areas; the analyzed treatments were in four cultivated areas: sorghum (So), forage cactos (Fc), massai grass (Mg), and buffel grass (Bg), implemented between strips of native vegetation (NTS) with different spacings of 7, 14, and 28 meters (S7, S14, and S28). These systems were compared with an area of native vegetation (NV) that was used as a reference. Soil samples were collected to depths of 0-50 cm. The distribution of stable aggregates in water was evaluated considering the following diameter classes: macroaggregates (>2.00 mm), mesoaggregates (2.00-0.25 mm), and microaggregates (0.25-0.053 mm). The mean weighted diameter (MWD), geometric mean diameter (GMD), aggregate stability index (ASI), and sensitivity index (SI) were calculated, in addition to the SOC associated with the aggregates. This study comprises two chapters. In Chapter 1, the analyses of aggregate stability at spacings of 7, 14, and 28 showed significant differences (p < 0.05) between the ILF systems when compared to the NV area. The distribution of aggregate classes indicated a predominance of mesoaggregates, followed by macroaggregates, and finally microaggregates, regardless of land use and the evaluated layers. The E28 demonstrated greater stability in the distribution of aggregates, specifically in systems integrated with buffel grass and sorghum. The MWD and GMD showed similar results among the ILF systems, NV, and NTS, mainly at the 7 and 14m spacings. The highest IS values were observed in the 30-50 cm layer, at all spacings, except in the systems with massai grass at the 7 and 28 m spacings. In chapter 2, NV and ILF systems showed higher carbon stocks in the mesoaggregates, especially in S28 with the systems integrated with buffel grass, massai, and sorghum. For the S7 spacing, only the VN in the 0-10 cm and 30-50 cm layers showed a higher SOC stock than the other analyzed systems. It is concluded that carbon stock occurs mainly in the mesoaggregates, and ILF systems are a sustainable alternative to improve soil carbon stock in the Brazilian semi-arid region, promoting sustenable agricultural practices with less impact. Keywords: Soil aggregates; C stock; Soil structure; Land-use change; Semi-arid; Integrated systems.