Abstract
Exclosure cages are often used for estimating biomass accumulation on continuously stocked pastures in grazing experiments. The microclimate inside the cages may affect the estimates of biomass accumulation, but this has not been previously identified or quantified. We evaluated how the exclusion from grazing for 21 days in Mulato II brachiariagrass (Brachiaria brizantha × Brachiaria decumbens × Brachiaria ruziziensis) pastures affected canopy air temperature (T) and relative humidity (RH) and how this related to biomass accumulation. We also evaluated the effect of the exclosure cage on wind speed (WS) and incoming solar radiation (SR), and how these impacted evapotranspiration (ET) and estimates of biomass accumulation on grazed canopies maintained at 20- and 30-cm height under continuous stocking. Regardless of canopy height, changes in canopy structure during the exclusion period up to 21 days did not affect T and RH (averages of 24.3 °C and 88.7%, respectively), indicating that the air circulation was not affected by the exclusion. The cage structure reduced SR by 5%, although there were times during clear days when SR was slightly greater inside the cage than outside. The cage also reduced WS by 4.4%. Smaller SR and WS resulted in less ET inside the cages than outside, although with close values (2.9 vs. 3.0 mm day−1; P = 0.0494). The biomass accumulation rate was greater inside than outside the cages for both canopy heights. This overestimation would be 5.8 and 9.7% greater if the structure of the cage did not reduce the SR, WS, and ET.
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The data supporting the findings of this study are available from the corresponding author, upon request.
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Acknowledgements
We thank Dr. F.A.P. Santos and Dr. M.A. Penatti for supplying the animals used in the experiment. We also thank Dr. C.Bosi for his help with modeling the growth of Mulato II brachiariagrass.
Funding
This study was supported by Coordination for the Improvement of Higher Education Personnel (CAPES, Finance Code 001) and by São Paulo Research Foundation (FAPESP; grant number 2017/11288–6) with a Doctoral Scholarship to the first author.
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J.I.Y., C.G.S.P., and P.C.S. designed the study; J.I.Y. analyzed the data and wrote the manuscript with contributions from C.G.S.P. and P.C.S.; J.I.Y., E.H., G.B.P., O.G.A., and S.G.H. conducted the experiments.
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The study was approved by the local Committee on Ethics in Animal Use (Protocol N° 2016–24).
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Yasuoka, J.I., Pedreira, C.G.S., Holcman, E. et al. Microclimate of grass canopies and biomass accumulation are influenced by the use of caged exclosures in grazing research. Int J Biometeorol 66, 45–54 (2022). https://doi.org/10.1007/s00484-021-02187-w
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DOI: https://doi.org/10.1007/s00484-021-02187-w