Silvopastoral systems:The presence of trees improves pasture quality

Forage in agroforestry integration showed a high crude protein content compared to a traditional livestock model – Photo: Gisele Rosso | Source: Embrapa.

The research, published in The Journal of Agricultural Science, concluded that shaded pasture has superior nutritional characteristics and similar productivity to pasture managed in full sunlight. (Read the scientific article: Productive and nutritive traits of Piatã palisadegrass after thinning the forest component of a silvopastoral system in southeastern Brazil)

According to Embrapa researcher José Ricardo Pezzopane, tree management in silvopastoral systems led to increased forage production compared to previous years. Prior to thinning, using the average of two seasons—two summers—which is the most productive period for pasture, forage production in the silvopastoral system was 45% lower than in the full sunlight system: 996 kilograms per hectare compared to 1.87 thousand kilograms per hectare, respectively. In the two summers following this management, the production was quite different: almost 2 thousand kilograms per hectare in the integrated model and 2.38 thousand kilograms per hectare in full sunlight. Pezzopane states that there is no statistical difference in this case.

Practices such as thinning or pruning are options to reduce resource competition between pasture and trees, ensuring balanced production among all elements of the system.

The study evaluated the productive and nutritional characteristics of Piatã grass (Urochloa brizantha cv. BRS Piatã) after thinning the forest component of the silvopastoral system, which consisted of eucalyptus (Eucalyptus urograndis clone GG100). Forage production and nutritional value, along with microclimate variables, were analyzed in the intensive full sunlight system with Piatã grass. The trial took place at Fazenda Canchim, the headquarters of Embrapa Pecuária Sudeste, in São Carlos (SP), from 2016 to 2018.

During the experimental period, the nutritional value and forage production were evaluated in five representative grazing cycles corresponding to the seasons from December 2016 to March 2018: summer, autumn, winter, and spring of 2017, and summer of 2018.

The crude protein content was higher in the silvopastoral system than in full sun in most seasons. However, the forage accumulation in both systems was similar. Forage production was favored by thinning, especially near the event, while its quality was consistently higher in the silvopastoral system.

• Therefore, Pezzopane recommends adopting tree thinning in integrated systems to provide forage production similar to full sun and, additionally, with a higher protein content.

Photo: José Pezzopane | Source: Embrapa

When farmers can efficiently use livestock and timber production in the same area, they enjoy various benefits. In addition to the alternative income from timber, there are ecosystem services such as species diversification and carbon fixation (C), which are often not accounted for.

However, Pezzopane warns that this model is quite complex because there are varied interactions among the elements: pasture, trees, and animals. “Positive results depend on the ability to ensure synergistic interactions between these components,” he states.

Producer Maria Fernanda Guerreiro, who has been working with integrated systems on her property since 2013, confirms the results of the Embrapa research in practice. She mentions that she has never had problems with shading from the trees because she always performs thinning. In addition to being a producer, Guerreiro is an agronomical engineer.

According to her, it is possible to visually perceive when management is needed; there is no need to have a radiation measurement device. It is necessary to observe and be attentive to all elements.

The right time for management is indicated by the level of light retention by the trees. Pezzopane recommends constant monitoring, and if it exceeds 35%, thinning should be done. Monitoring growth diameter and height, also helps to determine the ideal management point. Other indicators are the stabilization of tree growth, pasture vigor, and opportunities for wood exploitation for on-site use or sale.

Photo: Juliana Sussai | Source: Embrapa

The pasture quality in the silvopastoral system is related to higher soil fertility compared to intensive full-sun systems due to the diversification of soil organic matter (SOM) and its microbiota through root detachment of various species and litterfall. According to the study, SOM and its carbon result in a varied nitrogen mineralization rate, benefiting long-term nitrogen supplementation for plants.

In shaded environments with lower temperatures, enzymes exhibit reduced efficiency compared to pastures exposed to full sunlight during the process of photosynthesis. The decrease in efficiency results in a higher concentration of enzymes per leaf mass, and since a significant portion of leaf nitrogen is present in photosynthetic enzymes, there is a higher content of this nutrient in the leaf tissue.

The higher digestibility in silvopastoral pastures can be partially attributed to higher temperatures in the full sunlight system compared to the integrated system. Heating often increases the fiber content of forages, which reduces their quality and digestibility. High temperatures also promote the faster development of forage plants. Thus, it is possible that the pasture in the silvopastoral system was physiologically less mature than the pasture in full sunlight. This, in turn, contributes to higher digestibility since this characteristic of pasture generally decreases with the age of the plant.

• Balanced production can only occur with management practices such as thinning and pruning according to the needs of the production systems. The study pointed out that thinning in the silvopastoral system ensures superior nutritional characteristics and productivity similar to those of a pasture under full sunlight.
• Pastures in the integrated system have less available energy for growth compared to pastures in full sunlight. Thus, shaded plants adapt morphologically and physiologically to better utilize the available energy. Plants grown under low irradiation generally have thinner leaves with a high specific leaf area (SLA), which increases light interception. This is advantageous for the plant in low-light environments. The development of thinner leaves is an adaptation to reduce evapotranspiration by reducing the leaf area subjected to transpiration.

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