Despite the recognized importance of agriculture in food production and income generation, the sector has attracted attention due to the emission of Greenhouse Gases (GHG).
Brazil has the largest commercial cattle herd in the world, with 213,68 million heads, and is also the world's largest meat exporter (ABIEC, 2020). Despite the recognized importance of agriculture in food production and income generation, the sector has attracted attention for being one of the main emitters of Greenhouse Gases (GHG) in the country. In 2019, agriculture was responsible for 28% of Brazil's GHG emissions, behind only land use change, with 44% and ahead of the energy sector, with 19% of emissions. In the same year, the Brazilian herd was responsible for the emission of 366 million Megagrams of CO2 equivalent, which represented 60% of all agricultural emissions, or 16,8% of Brazil's GHG emissions (SEEG, 2020).
Although livestock productivity has grown in the last 20 years, another problem in this sector is low animal productivity, resulting from the extensive system, in areas of unproductive and degraded pastures. Livestock farming occupies 162,53 million hectares of land in Brazil. The average animal capacity of 1,31 heads ha-1 year-1 or 1,06 AU - Animal Unit ha-1, and productivity of 4,4 @ ha-1 year-1 (ABIEC, 2020).
Of the total land occupied by pastures in Brazil, a large part is in some stage of degradation. Data on pasture degradation in Brazil is still inaccurate, ranging from 63,74 million hectares (LAPIG, 2017) to 15,5 million hectares (ABIEC, 2020). When considering cattle fattening, a degraded pasture can produce up to six times less than a recovered pasture or one in a good state of maintenance (MACEDO et al., 2000).
The main cause of pasture degradation is incorrect grazing management, which maintains an animal stocking rate greater than the support capacity. This occurs mainly during the dry period, when there is a low supply of forage and low carrying capacity. In extensive continuous grazing systems, animals frequently eat forage regrowth. This overgrazing, without a rest period, weakens the pasture and stops covering the soil. The uncovered area is heated and becomes compact over time, reducing water infiltration, increasing erosion and causing loss of soil and fertility.
On the other hand, according to the FAO report (2006), productive pastures, well managed, represent the second largest potential global source of carbon sequestration (C), with the capacity to remove 1,7 billion Mg of carbon from the atmosphere. C per year, second only to forests, whose estimated capacity reaches 2 billion Mg of C per year. Tropical pastures also play an important role in soil quality, promoting structuring, facilitating water infiltration and increasing total carbon in the soil profile.
As a way to reduce GHG emissions in agriculture, the Brazilian government adopted, in 2010, the “ABC agriculture, low carbon agriculture” plan. It establishes special credit lines for agricultural practices that promote the improvement of pastures and management practices integrated with agriculture and/or forests through Agropastoral Systems such as Crop-Livestock Integration (ILP), Agroforestry, or Crop-Livestock-Forest Integration (ILPF ), Silvopastoral or Livestock-Forest Integration (IPF).
The association of legume species with grasses improves soil fertility, customer service forage and animal productivity. She TIt also avoids the burning of fossil fuels to produce nitrogen fertilizers and contributes to mitigating the emission of volatilized nitrogen, which greatly contributes to reducing GHG emissions. Intensive Rotated Grazing Systems (SR), if well managed, are capable of sustaining good productivity, improving the production environment. However, it is not common for them to be able to eliminate the balance of emissions and carbon sequestration from livestock farming. Only when livestock farming introduces the arboreal element into the system is there a zero or even negative balance of emissions - that is, there is more sequestration than emissions (BALBINO et al. 2011a; VARSHA et al. 2019; LIN et al. 2020).
Considering the economic and environmental importance of livestock farming, mainly due to the significant area of land occupied in Brazil, but also due to the low animal productivity, soil degradation and high emissions of Greenhouse Gases (GHG) in extensive management, it is essential to implement systems more sustainable livestock farming, with productive, well-managed pastures, in consortium with tree species, leguminous shrubs and integrated into crops. There is enormous potential for improving the physical attributes of the soil, sequestering carbon, and increasing plant and animal productivity.
Considering these issues, the master's thesis by agricultural engineer Osvaldo Viu Serrano Júnior, carried out under the guidance of Professor Zigomar Menezes de Souza, from the Faculty of Agricultural Engineering (Feagri) at Unicamp (titled Physical quality, soil carbon stock and animal productivity of different Regenerative Silvopastoral Systems), sought to evaluate the influence of different livestock production systems - Rotational Grazing System (SR), Silvopastoral System (SSP) and Intensive Silvopastoral System (SSPI with leucaena and tithonia) - on the physical attributes of the soil, carbon stock and the productivity of Nelore animals.
The research was carried out at Fazenda Takaoka, municipality of Iaras, State of São Paulo. The systems evaluated were: IT – Intensive Silvopastoral System (SSPI with leucaena), grass Panicum maximum (cv. BRS Zuri), in consortium with Leucena (Leucaena leucocephala) (cv. Cunningham) and rows of tree species every 20 m; T2 – Intensive Silvopastoral System (SSPI with tithonia), grasses Panicum maximum (cv. BRS Zuri), in consortium with Titônia (Tithonia diversifolia) and rows of tree species every 20 m; T3 – Silvopastoral System (SSP), grasses Panicum maximum (cv. BRS Zuri), with rows of tree species every 20 m; T4 – Rotated Grazing System (SR), grasses Panicum maximum (cv. BRS Zuri). The rows of tree species (Forest Bands – FF) in the T1, T2 and T3 systems were composed of the forest species African Mahogany (Khaya Ivorenses), Leucena (Leucaena leucocephala), Eucalyptus (Eucalyptus urograndis), Acacia (Acacia mangium) and Gliricidia (Gliricidia sepium). Each system covers an area of 11 ha, divided into 16 paddocks, resulting in a total area of 44 ha.
Search results:
- One of the main results obtained in the research was the increase in animal productivity. All intensive grazing systems studied showed good results in terms of productivity, on average 35,9@ ha-1 year-1, which is practically nine times the national average productivity. According to Serrano Jr., “we have technology in Brazil for greater productivity in livestock farming, which would allow increasing national production with less land occupation, freeing up deforested area for agricultural growth and reducing pressure on deforestation. And animals produced by higher productivity livestock emit less GHG throughout their lives, instead of being slaughtered at 30 months, they now have a shorter life cycle, of 18 to 20 months, reducing emissions per animal” .
- Another relevant result was in relation to carbon sequestration in the soil of the Leucena silvopastoral system, with an average carbon increase of 1,95 Mg C ha-1 year-1 in the first year of study. Showing enormous potential for pasture production systems combined with leguminous shrubs to improve carbon sequestration.
- The silvopastoral systems in a consortium of grasses with shrubby forages, SSPI of leucaena and tithonia (T1 and T2), respectively, also presented lower values of soil density, soil resistance to penetration and animal productivity and higher values of macroporosity, stability index of aggregates and water retention in the soil, resulting in greater field capacity, greater available water capacity and carbon stock, compared to grass production systems without intercropping, SR and SSP (T3 and T4), respectively.
- The Intensive and Regenerative Silvopastoral system, in addition to reducing greenhouse gas emissions per animal and pressure on deforestation, presents several synergies between animal production and shrub and arboreal elements, is scalable and removes livestock farming from emitter status of GHG to be an activity with enormous potential for carbon sequestration in Brazil and the world.
- The effect of planting grasses in consortium with forage shrubs, forest strips and rotational grazing management should cause even more significant changes in the production environment over time, demonstrating the importance of continuing this study. More studies will also be needed to evaluate the best combinations between shrub or herbaceous legumes with different types of grass, different management in different regions of the country.
