For continuously stocked pastures, net forage accumulation is thought to be relatively unaffected across a rather large range of canopy‐based management targets. It is not known whether this is also characteristic of intermittently stocked canopies, and if so, the underlying mechanisms have not been well delineated. We hypothesized that initiation of grazing when canopy heights are shorter than heights corresponding to the critical leaf area index, associated with a moderate intensity of defoliation, do not reduce forage accumulation in pastures under intermittent stocking. Therefore, kikuyugrass (Pennisetum clandestinum Hochst. Ex Chiov) pastures were grazed at four pregrazing heights (10, 15, 20, and 25 cm) with the same proportion of defoliation (50% reduction in pregrazing height; i.e., postgrazing heights of 5, 7.5, 10, and 12.5 cm, respectively) from December 2011 to May 2013. As the canopy height increased, there was an inverse relationship between tiller weight and number; however, heavier tillers presented greater rates of leaf elongation. Pastures grazed at 15 to 25 cm had the same forage accumulation. The same homeostatic mechanisms that keep a constant forage accumulation in different heights when pastures are subjected to continuous stocking also allowed for a similar forage accumulation in pastures under intermittent stocking at different grazing heights.

Grass species can be classified into different functional types based on their growth strategies, and contrasting persistence strategies are observed in different grass species. Excluding seedling recruitments, changes in populations of grasses are basically a trade-off between natality and mortality of tillers. We hypothesised that the persistence pathway of perennial grasses is linked to their growth strategy, regardless whether they are growing as monoculture or as a mixture. Species with contrasting growth strategies (Arrhenatherum elatius L., Dactylis glomerata L., and Festuca arundinacea Schreb.) were cultivated as monocultures and as a mixture and their tiller natality and mortality were evaluated for two years after swards establishment. All pastures maintained their population size during the experimental period, although decreases in tiller densities occurred during the warmer season. Arrhenatherum elatius had the highest tiller mortality and natality whereas the F. arundinacea had the lowest ones. Arrhenatherum elatius had many tillers appearing in all seasons but their tillers were short-lived. Conversely, F. arundinacea and D. glomerata developed numerous tillers during autumn and winter and their tillers survived, on average, almost six and three times longer than those of A. elatius, respectively. There were no differences in tillering dynamics among populations grown in monocultures or in the mixture. Regardless of whether they were cultivated in monocultures or as a mixture, the persistence pathway of perennial grasses is linked with their growth strategies with exploitative species presenting a high tiller turnover throughout the year whereas the persistence of more conservative species is based on a high tiller survival.

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 23 cm, 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 10 cm diameter 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 7400 kg 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.

It is well reported in the scientific literature that pastures can have similar net forage accumulation when managed with contrasting structures. However, we hypothesized that the dynamics of forage accumulation in grazed swards is linked to seasonal‐environmental conditions. Marandu palisadegrass (Brachiaria brizantha [Hochst. ex A. Rich.] was used as the forage species model. The experimental treatments were four grazing heights (10, 20, 30 and 40 cm) allocated to experimental units according to a randomized complete block design with four replicates and evaluated throughout four contrasting environmental seasons (summer, autumn, winter–early spring and late spring). Under rainy and warm periods, greater net forage accumulation was observed in pastures maintained taller; on the contrary, during the mild and dry periods, net forage accumulation rate reduced as grazing height increased. Such patterns of responses were related to compensations between tiller population density and tissues flows during summer and late spring and the reduced capacity of taller canopies to compensate lower population with greater growth rates during autumn and winter–early spring. Grazed swards changed their patterns of forage growth as they transitioned from favourable to more abiotic stressful conditions, suggesting that seasonal adjustments in grazing intensities are necessary in order to maximize forage production.

This study evaluated the leaf area index (LAI) recovery mechanisms and forage accumulation rates on the regrowth of different grass species subjected to different defoliation intensities. For that purpose, plots of Pennisetum clandestinum (kikuyugrass), Lolium multiflorum (annual ryegrass), and Avena strigosa (black oats) were defoliated from 20 to 80 % of their initial heights (25, 20, and 25 cm, respectively). At different increments in height, forage samples were collected to ground level and used to estimate tiller population density (TPD), leaf area per tiller (L A), and forage mass. From these data, we calculated the leaf area index (LAI), average leaf area index (aLAI), and average and instantaneous forage accumulation rate (FAR and IFAR, respectively). Data were plotted over time (days) to describe LAI recovery and forage accumulation rates. As the defoliation intensity increased, greater canopy heights were needed for pastures to achieve their maximum forage accumulation rates, which required longer regrowth intervals. The need for high tiller recruitment after defoliation, which delayed canopy LAI recovery, seemed to be one of the main cause. Thus, grazing management strategies that involve costly tiller recruitment could decrease both overall forage production and sward persistence over time. However, the plant ability to recover LAI after successive intense defoliations seems to be species-dependent and related to their phenotypic plasticity.

Multi-species pastures have been viewed as a means to increase forage production relative to monocultures through enhanced three-dimensional occupation of the canopy, which will intercept and use the incident radiation more efficiently. For this to occur, increased production of photosynthetically active tissues such as leaves is required. We tested the hypothesis that intercropping of black oats (Avena strigosa Schum.) and annual ryegrass (Lolium multiflorum Lam.) can increase total and leaf forage production compared with their monocultures. Monocultures and mixed pastures of black oat and annual ryegrass were established, and their tiller morphogenetic and structural traits, as well as components of herbage production, were measured throughout the usage period of the pastures. There was no difference between treatments for total growth rate (77.1 kg dry matter (DM) ha–1 day–1), but annual ryegrass pastures presented the greatest stem growth rate (38.1 kg DM ha–1 day–1). Taking into account only the vegetative phase, the intercropped pasture produced 20% more leaf than the monocultures. There were no differences between species, either in monoculture or intercropped, for phyllochron, final leaf length, leaf elongation duration and leaf elongation rate. The most important modification in morphogenetic variables due to the inter-specific competition was an increase in senescence rate of annual ryegrass leaves. The average specific green leaf weight in the intercropping pastures corresponded to 84.6% and 137.5% of those values observed for black oat and annual ryegrass pastures, respectively. On the other hand, the intercropping pastures presented 43.5% more tillers than the black oat pastures and 17.8% fewer tillers than the annual ryegrass pastures. It is suggested that intercropping black oat and annual ryegrass does not change tiller ontogenetic processes and that the association of their different size and shape in intercropped pastures could increase pasture leaf production over their monocultures.

Annual temperate grasses go through abrupt changes in morphological composition during the growing season, which can affect ingestive behavior of grazing cattle. However, few studies have examined the effects of gradual structural changes in annual temperate pastures on the herbage intake rate during the growing season. We hypothesized that lenient grazing (removal of 40% of the initial pre‐grazing height) maintains short‐term intake rate (STIR) of grazing cattle over the entire growing season, even with decreased leaf/stem ratios. The studied pastures contained Avena strigosa, Lolium multiflorum and a mixture of the two species. Short‐term intake rate was measured using the double weighing technique, evaluating both bite rate and bite mass. The percentage of stem + pseudostem and leaf lamina lengths in the herbage mass were measured. Relationships between sward structure and animal ingestive behavior were also examined. As the pasture growing season progressed, the STIR of heifers grazing annual temperate grass swards was affected more by the time required to take a bite than by bite mass. Moreover, the sward structure also changed after each grazing cycle, reducing the pre‐grazing leaf/stem ratio. However, reductions in the pre‐grazing leaf lamina mass (up to 37% of the sward herbage mass) and/or in the leaf lamina length (up to 52% of the extended tiller height) did not affect the STIR of grazing heifers, since the animals maintained their bite mass and time per bite. In summary, with a grazing down target of 40% of the pre‐grazing height, reductions in STIR of heifers grazing annual temperate grasses occurred when the pre‐grazing leaf lamina percentage was <37% of the sward herbage mass and/or <52% of the extended tiller height. These results suggested that to avoid STIR reductions during the last grazing cycles, managements to stimulate tillering and delay stem + pseudostem elongation are necessary and should be investigated.

SUMMARYMixing species with different tillering peaks may enhance pasture stability, but intercropping may also alter the plants’ tillering patterns. This study aimed to evaluate tillering dynamics in black oat (Avena strigosa Schreb.) and annual ryegrass (Lolium multiflorum Lam.) pastures grown as monocultures or intercropped. Three following treatments are established: black oat and annual ryegrass pastures grown as monocultures and an intercrop composed of these two species. Tillering dynamics were measured for black oat and annual ryegrass populations separately. When intercropped, tiller birth rates of black oat decreased (20.0 vs. 28.9 tillers 100 tillers−1) and those of annual ryegrass increased (30.5 vs. 14.3 tillers 100 tillers−1), compared to their monocultures. Tiller death rates for annual ryegrass did not differ between monoculture and intercropping (23.9 tillers 100 tillers−1), but black oat presented higher mortality in monocultures (48.8 vs. 36.4 tillers 100 tillers−1). The black oat monoculture had the lowest population stability index (0.80), whereas annual ryegrass in monoculture and intercropped pastures exhibited greater values (on average, 0.92). Our results indicated that black oat and annual ryegrass present distinct tillering dynamics whether grown as monoculture or intercropped, and suggest that intercropping species with elevated death rates (black oat) with later species (annual ryegrass) could be an important tool for maintaining pasture stability throughout the growing season.