The silvopastoral systems (SSPs) have as objective to increase the sustainability of
agriculture, combining the following components: animals, pasture, and trees species.
However, such combination changes the environment, mainly the microclimate, the plants
growth, and also the animal production. Based on the changes caused by the SSPs, the
objective of the present study was to evaluate the microclimate changes in a SSP under
grazing, in São Carlos, SP, Brazil, promoted by the presence of trees, to correlate the changes
in microclimate with the pasture yield and to parameterize the FAO Agroecological Zone
model (FAO-MZA) to estimate the Brachiaria brizantha, growth in full sun, and lately the
growth of B. decumbens in a SSP. For that, the micrometeorological variables were
continuously monitored by four weather stations distributed in different positions inside the
SSP: at 2 m from the trees at east (2mL); at 6 m from the trees at east (6mL); at 6 m from the
trees at west (6mO); and at 2 m from the trees at west (2mO), in order to evaluate the
microclimate and yield along a transect between two rows of trees. Another weather station
was also installed out of the SSP, in a full sunny condition, and it was considered as reference.
The biometric characteristics and the yield of the pasture plants were also measured during
seven cycles of 35 days. During each crop cycle, five evaluations were done to determine the
growth dynamics of the plants. These data were used to parameterize the FAO-MZA model
for estimating the B. decumbens and B. brizantha yields. The results showed that the
microclimate was modified by the presence of trees, but with the intensity of change
depending on the level of shading, the season of year (solar declination), the orientation of the
rows, the vertical influence of the tree canopy to retain the long-wave radiation, and the wind
speed. Regarding the variables related to the pasture, the shading affected the yield and the
biometric characteristics of the plants, in the first three cycles, when more than 50% shading
occurred, there was a reduction of yield and leaf area index, as a consequence of the increase
in plant height and specific leaf area (AFE), as a strategy to increase the uptake of solar
energy. However, when water and/or thermal stresses occurred no differences were observed
among the treatments for all the variables. It demonstrates that the shading loses its influence
over the pasture growth when there are other environmental limiting factors. The FAO-MZA
model had a good performance for estimating the potential yield for B. brizantha growing in a
full sunny condition, and also for the attainable yield of B. decumbens at low levels of
shading. However, the model was not able to estimate the attainable yield of B. brizantha in a
full sunny condition, which was caused by inconsistencies of the pasture yield data under
irrigation, which was not possible to be modeled, and of B. decumbens in high levels of
shading, because the model does not consider the plants ́ phenotypic plasticity effect, which
makes the pasture more yield conservative under shading.
