Seasonal alteration in sward height of Marandu palisade grass (Brachiaria brizantha) pastures managed by continuous grazing interferes with forage production Suleize Terra A , Flávia Maria de Andrade Gimenes A , Alessandra Aparecida Giacomini A,C , Luciana Gerdes A , Marisa Xavier Man¸ co B , Waldssimiler Teixeira de Mattos A , and Karina Batista A A Instituto de Zootecnia, Rua Heitor Penteado 56, CP 13380-011, Nova Odessa, SP, Brazil. B Faculdade de Zootecnia e Engenharia de Alimentos da Universidade de São Paulo, Rua Duque de Caxias 221, CP 13635-900, Pirassununga, SP, Brazil. C Corresponding author. Email: giacomini@iz.sp.gov.br Abstract. Changes in sward height of pastures managed by continuous grazing according to climatic seasonality may alter tillering and forage production. In order to evaluate the feasibility of seasonal alteration in sward height of Marandu palisade grass pastures (Brachiaria brizantha (Hochst. ex A.Rich.) R.D. Webster; syn. Urochloa brizantha (A.Rich.) Stapf) under continuous grazing management, we studied two constant sward heights (15 cm and 30 cm), and one height that was initiated at 30 cm, reduced to 15 cm in June (dry and cold season) and returned to 30 cm in December (wet and hot season) (30–15–30 cm). Pastures managed at 30–15–30 cm had a greater tiller appearance rate (22 tillers/100 tillers.30 days) than those maintained at 15 cm and 30 cm (16 and 17 tillers/100 tillers.30 days, respectively). In the 30–15–30 cm pastures, a lower accumulation rate of dead material was observed during the dry and cold season (June–August), which resulted in a higher leaf and lower dead material accumulation rate during the second growth season (wet and hot season, December–January). Planned reduction in sward height during the cold season can be used safely because it permits better seasonal distribution and utilisation of forage production without compromising the stability of Marandu palisade grass pastures. Additional keywords: forage accumulation, stability index, tiller appearance, tiller population density, Urochloa spp. Received 12 April 2019, accepted 26 November 2019, published online 2 March 2020 Introduction Continuous grazing with variable stocking rate based on sward height targets is used for tropical grasses, and targets have been defined for some grasses of the genus Urochloa (Sbrissia et al. 2010; Euclides et al. 2016). Pasture management based on targets for the control of sward height influences tiller dynamics (Sbrissia et al. 2010; Santana et al. 2017), forage accumulation (Pedreira and Pedreira 2007), and animal productivity (Flores et al. 2008). For Marandu palisade grass pastures (Brachiaria brizantha (Hochst. ex A.Rich.) R.D. Webster; syn. Urochloa brizantha (A.Rich.) Stapf) (Jank et al. 2014), the grazing-management targets that optimise forage production and animal performance consist of a constant sward height ranging from 20 to 40 cm over the year (Flores et al. 2008; Sbrissia et al. 2010; Da Silva et al. 2013). During the period of limited environmental resources (i.e. water, light and temperature), called the critical period (cold and dry season of the year), plant growth decreases and tissue senescence increases. Pastures managed at taller sward heights during the critical period are characterised by a greater decline in forage production and greater increase in tissue senescence than pastures maintained at lower sward heights (Da Silva et al. 2013). As a result, the proportion of dead material increases, which can hinder the passage of light to the base of the canopy and impair the appearance of new tillers and consequent pasture recovery after re-establishment of favourable environmental conditions (hot and wet weather) for growth (Sbrissia et al. 2010; Da Silva et al. 2013). In this regard, Marandu palisade grass is characterised by high tiller turnover at the end of spring and the beginning of summer in tropical climates (Giacomini et al. 2009; Sbrissia et al. 2010). Tiller population dynamics determine the mechanistic processes of forage production and changes in the morphological composition of the forage produced (Matthew et al. 2000). Within this context, important studies are those that aim at identifying management strategies that reconcile with the natural cycles of plants, favouring plant growth and production (Da Silva et al. 2015b). Marandu palisade grass is the most widely used grass in Brazil, occupying ~60 Mha of the 194 Mha utilised for pasture Journal compilation Ó CSIRO 2020 www.publish.csiro.au/journals/cp CSIRO PUBLISHING Crop & Pasture Science https://doi.org/10.1071/CP19156