Peer review

Understanding plant growth may help to identify factors limiting forage production and contribute to the identification of optimal harvest management. The objective of this study was to describe and explain the effect of two harvest intervals (28 and 42 d) on the growth of Convert HD 364 (Dow AgroSciences, São Paulo, Brazil) hybrid brachiariagrass (Brachiariaspp., syn. Urochloa spp.), ?Marandu? palisadegrass [Brachiaria brizantha (Hochst. ex A. Rich.) RD Webster, syn. Urochloa brizantha (A. Rich.) Stapf; CIAT 6297], and ?Tifton 85? bermudagrass (Cynodon spp.). The experimental design was a randomized complete block with a factorial combination of three grasses and two harvest intervals (n = 4). The following variables were evaluated during two consecutive years: Leaf area index (LAI), crop growth rate (CGR), relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR) and leaf weight ratio (LWR). Marandu palisadegrass showed the least CGR (44.4 kg ha?1 d?1) compared with Convert HD 364 and Tifton 85 (?52 kg ha?1 d?1). Longer harvest interval resulted in greater CGR (55.4 vs. 43.5 kg ha?1 d?1), but generally a lesser RGR, suggesting a reduction in efficiency of growth under 42-d harvest intervals. Tifton 85 uses less leaf area to produce similar or greater herbage mass due to greater leaf photosynthetic efficiency, as it had greater NAR and lesser LAI, but similar CGR compared with Convert HD 364. The harvest interval of 28 d results in greater C partitioning to leaf and to build leaf area, increasing the leaf proportion in harvested forage.

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