Tiller size/density compensation in temperate climate grasses grown in monoculture or in intercropping systems under intermittent grazing

Oat and ryegrass intercropping in pastures is widely used in regions with subtropical climates. The aim of this study was to evaluate the tiller size/density compensation mechanisms in monoculture and intercropping swards of black oats (Avena strigosa Schreb cv. IAPAR 61) and annual ryegrass (Lolium multiflorum Lam. cv common) under intermittent grazing. Treatments (black oat, annual ryegrass and their mixture) were assigned according to a complete randomized block design with four replicates. Ryegrass, oat and intercropped pastures were grazed when the swards reached a height of 17, 25 and 23cm, respectively, and with a level of defoliation of 40%. The aerial biomass was determined with a rising plate meter, and the tiller population density (TPD) was estimated by counting tillers in three 10cmdiameter PVC rings per paddock. The mass per tiller was estimated based on the aerial biomass and the TPD of each paddock. Total herbage production did not differ among treatments, with values around 7400kg DM ha(-1). TPD decreased and mass per tiller increased linearly in the monoculture treatments. Tiller size/density compensation was observed in the three plant communities (treatments) according to the self-thinning rule. In addition, no relationships were found when each species was analysed individually in the intercrop treatment. The results suggest that species in grass mixed swards adjust their population to keep a relatively constant leaf area index (LAI) over the grazing seasons, and that would help pastures to stabilize herbage production.