Growth of Megathyrsus maximus cv. Mombaca as affected by grazing strategies and environmental seasonality. II. Dynamics of herbage accumulation

Author(s)

Carnevalli, Roberta Aparecida ^[1] ; Congio, Guilhermo Francklin de Souza ^{[2, 3]} ; Sbrissia, Andre Fischer ^[4] ; da Silva, Sila Carneiro ^[2]

Affiliation

^[1] Embrapa Dairy Cattle, Brazilian Agr Res Corp, Ave Eugenio do Nascimento 610 Aeroporto, BR-36038330 Juiz De Fora, MG - Brazil

^[2] Univ Sao Paulo, Luiz de Queiroz Coll Agr, Dept Anim Sci, Ave Padua Dias 11, BR-13418900 Piracicaba, SP - Brazil

^[3] Agrosavia, Colombian Corp Agr Res, Km 14 Via Mosquera Bogota, Mosquera 250047, Cundinamarca - Colombia

^[4] Santa Catarina State Univ, Dept Anim Prod & Food Sci, Ave Luiz de Camoes 2090, BR-88520000 Lages, SC - Brazil

• Document type: Journal article
• Source: CROP & PASTURE SCIENCE; v. 72, n. 1 JAN 2021.
• Web of Science Citations: 1

Abstract

For tropical forage grasses, leaves are the main morphological component accumulated at the beginning of regrowth, and as leaf area index increases, plants change their growth pattern, allocating more resources to stem elongation as a means of optimising light capture. We hypothesised that, for Mombaca guineagrass, stem elongation and leaf senescence rate play a major role in determining net herbage accumulation rate (NHAR) and that senescence would be the key factor driving the reduction in NHAR when regrowth is interrupted beyond the critical leaf area index, that is, when canopy light interception (LI) exceeds 95%. Treatments corresponded to all combinations of two levels of pre-grazing canopy LI during regrowth (LI95% and LIMax) and two post-grazing heights (30 and 50 cm), and were allocated to experimental units according to a randomised complete block design with four replications. Measurements were performed throughout contrasting climatic conditions during four seasons from January 2001 to February 2002. Overall, spring and the two summers were the seasons when rates of leaf appearance, leaf elongation and leaf growth rate were higher, and leaf lifespan was smaller; the inverse occurred during autumn-winter. Despite the lack of statistically significant differences in NHAR between LI treatments during some seasons of the year, the ratio of leaf growth rate to NHAR was consistently higher for LI95% than LIMax. The pre-grazing target of LI95% was also efficient for decreasing stem elongation and leaf senescence rate. Increased senescence on individual tillers was the key driver generating modifications in the patterns of variation in NHAR beyond the critical leaf area index, suggesting that there is no advantage in extending the regrowth period when the main objective is to maximise leaf growth rate or NHAR. (AU)