Presence of trees improves pasture quality

Research by Embrapa Pecuária Sudeste (SP) proved that tree management is strategic to ensure balance in livestock-forest integration (IPF) or silvopastoral systems. In addition to maintaining pasture productivity and improving the quality of the remaining wood, the forage in this system had a high crude protein content, when compared to a traditional livestock model, without the presence of the arboreal component, which means higher quality of food for the animals. .

The advance is important because maintaining forage production in systems integrated with trees is a challenge for rural producers, since the development of pastures depends on the incidence of light. The decrease in radiation affects the growth of these plants, which may lead to lower productivity in livestock farming.

Silvopastoral systems are sustainable options for livestock farmers to intensify pastures. With trees integrated into livestock farming, the producer provides animal welfare and contributes to the removal of atmospheric carbon and mitigation of greenhouse gas (GHG) emissions. Not to mention that the arboreal component is a good bet to guarantee carbon credits in the future, a new income alternative.

The work, published in The Journal of Agricultural Science, concluded that a shaded pasture has superior nutritional characteristics and productivity similar to those of a full-sun pasture managed in the same way. (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, the management of trees in the silvopastoral system provided an increase in forage production compared to previous years. Before thinning, using the average of two seasons – two summers –, which is the most productive pasture season, forage production in silvopastoral was 45% lower than in the full sun system: 996 kilos per hectare compared to 1,87 thousand kilos per hectare, respectively. In the two summers following management, production was very different: almost 2 thousand kilos per hectare in the integrated model and 2,38 thousand kilos per hectare in full sun. According to Pezzopane, there is no statistical difference in this case. “In addition to no variation in production, the forage in silvopastoral had higher levels of crude protein, which represents a higher quality of food for the animals. It is important to highlight that the two systems were managed under the same type of grazing, that is, rotated with nitrogen fertilization of the pasture”, explains the researcher.

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

Results

Crude protein content was higher in IPF than in full sun in most seasons. Forage accumulation in both systems was similar. Forage production was favored by thinning, especially close to the event, while its quality was consistently higher in the IPF.

Therefore, Pezzopane recommends the adoption of tree thinning in integrated systems to provide forage production similar to full sun and, even, with a higher protein content.

When the rancher is able to use livestock and wood production efficiently in the same area, he has several benefits. In addition to alternative income from wood, there are ecosystem services such as species diversification and carbon (C) fixation, which are generally not computed. However, Pezzopane warns that this model is quite complex, because there are varied interactions between the elements: pasture, trees and animals. “Positive results depend on the ability to guarantee synergistic interactions between such components,” he says.

Producer Maria Fernanda Guerreiro, who has been working with integrated systems on her property since 2013, confirms the results of Embrapa's research in practice. She says that she never had any problems with the shading of the trees, because she always thinned them. In addition to being a producer, Guerreiro is an agricultural engineer. “I have a photosynthetically active light radiation (PAR) meter at the site. So, I never had any problems with the shading of the pasture, on the contrary, I only had benefits. I worked with pruning and thinning eucalyptus trees. When the meter showed shading exceeding 35%, we came up with a form of management. I removed the thinnest plants, the sick ones, and so I didn’t have any problems,” she says.

According to her, it is possible to visually understand when to handle; It is not necessary to have radiation measuring equipment. It is necessary to observe and be attentive to all the 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 carried out. Checking the growth in diameter and height also contributes to defining the ideal management point. Other indicators are the stabilization of tree growth, vigor of pastures and opportunities to exploit wood for use on the property or for sale.

The quality of pasture in silvopastoral is related to greater soil fertility compared to intensive systems in full sun due to the diversification of soil organic matter (SOM) and its microbiota due to the detachment of roots of different species and the fall of litter. According to the study, SOM and its carbon result in varied nitrogen mineralization rates, benefiting nitrogen supplementation for plants in the long term. “This factor, with the physiological changes caused by shading, generally results in species with higher crude protein content and in vitro dry matter digestibility compared to those managed in full sun, which explains the higher crude protein content of forage in most seasons when compared to intensive full sun positions,” details the researcher.

“In addition, the presence of trees reduces surface runoff and allows deeper layers of the soil to be explored to capture water which, under conditions of adequate water availability, increases the total use of water by the system. Furthermore, the shade reduces radiation and thermal stress in cattle, which can result in greater animal performance”, indicates the researcher in the work.

Under shade in environments with lower temperatures, enzymes are less efficient than in pastures in full sun, in the photosynthesis process. The decrease in efficiency results in a greater concentration of enzymes per leaf mass and, as a large part of the nitrogen in the leaf is present in photosynthesis enzymes, there is a greater content of this nutrient in the leaf tissue.

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

Tree management brings more quality and productivity

Balanced production will only occur with management practices such as thinning and pruning according to the needs of the production systems. The study showed that thinning in silvopastoral guarantees the pasture superior nutritional characteristics and productivity similar to those of a pasture in full sun.

Pastures in IPF have less energy available for growth compared to pastures in full sun. Thus, shaded plants adapt morphologically and physiologically to make better use of the available energy. Plants grown under low irradiation generally have thinner leaves with high specific leaf area (SFA), 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, reducing the leaf area subjected to transpiration.