Light interception measurements of Brachiaria decumbens cv. Basilisk and Brachiaria brizantha cv. Xaraés along regrowth process using commercial instrumentation

• Grant number: 15/12617-8
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: November 01, 2015
• End date: October 31, 2016
• Field of knowledge: Agronomical Sciences - Animal Husbandry - Pastures and Forage Crops
• Principal Investigator: Lilian Elgalise Techio Pereira
• Grantee: Júlio César Mioto
• Host Institution: Faculdade de Zootecnia e Engenharia de Alimentos (FZEA). Universidade de São Paulo (USP). Pirassununga , SP, Brazil

Abstract

The light interception (LI) has been used as a criterion for defining the pre-grazing condition, once it has high correlation with the sward height, which consists and efficient field indicator, quickly and easily measured, allowing adequate control of the sward structure. Although this correlation has been reported for many grasses, differences between the sward height in the moment when the canopy intercepts 95% of LI have been recorded between experiments. Some of these differences may be linked to differences in LI measurements obtained by different devices (commercial instruments) or the lack of standardization in the number of reading stations. The devices most used in Brazil are AccuPAR model LP-80 and LI-COR LAI-2000 model. The possible differences between the measurements obtained by these devices are unknown, since studies in pastures have not yet been conducted. For this purpose will be performed two experiments in swards of Brachiaria brizantha cv. Marandu and B. decumbens cv. Basilisk. Experiment 1 will be held for standardization of light interception measurements obtained with AccuPAR model LP 80 (Decagon Devices®, USA) and LI-COR LAI 2000 model (Li-Cor, Lincoln Nebraska, USA) in small plots (80 m²). To standardize measurements, the following protocols (P) will be tested with two devices: a) P1x5 = 1 reading station, composed by one reading above the canopy and five at ground level; b) P1x10: one reading above the canopy and ten at ground level; c) P2x5: 2 reading stations, each one composed by one reading above the canopy and five at ground level; d) P2x10: 2 reading stations, each one composed by one reading above the canopy and 10 at ground level. Treatments will be distributed in a factorial arrangement 2 x 4, comprising two measuring devices and four reading protocols, distributed in a randomized complete block design, where two previously trained evaluators will consist the blocks, with six replications on each block (experimental plots 80m²). In experiment 2 will be compared the accuracy of light interception measurements obtained with AccuPAR model LP 80 (Decagon Devices®, USA) and LI-COR LAI 2000 model (Li-Cor, Lincoln Nebraska, USA) in pre- and post-grazing conditions in order to understand how the architecture and sward structure can interfere with the measurements obtained. Thus, for each grass species treatments consist of two commercial instruments and two sward conditions (post and pre-grazing) and will be distributed in a randomized complete block design in a 2 x 2 factorial arrangement, where each evaluator consist a block and six replications (plots). (AU)