Unraveling the forage productivity puzzle: Comparing fast and slow-growing grasses.

Functional traits are powerful tools for distinguishing between plants with different resource acquisition strategies. Fast-growing plants normally dominate resource-rich habitats and present trait values associated with high productivity, such as high specific leaf area (SLA), short leaf lifespan, and rapid leaf elongation rate (LER). In contrast, slow-growing species have a higher leaf weight ratio (LWR), leaf lifespan (LLS), and phyllochron, which are useful traits for survival in stressful and unfertile environments, but are normally thought to be incompatible with high productivity, even under fertile conditions. We tested the hypothesis that slow-growing forage grasses have demographic parameters (tiller population density and canopy density) that offset their slow individual traits, making them as productive as fast-growing species when grown in fertile soil. Species with contrasting growth strategies (Arrhenatherum elatius L. and Festuca arundinacea Schreb cv. Quantum II, fast and slow-growing species, respectively) were cultivated in 45 m2 field plots and subjected to the same cutting regime and nitrogen supply level. Functional traits and canopy attributes were continuously measured during 8 growing cycles after the establishment of the swards. A. elatius had higher SLA, LER, leaf senescence, and leaf appearance rates, whereas F. arundinacea had higher LLS and LWR values. Conversely, there were no differences in relative growth rate or forage accumulation. F. arundinacea was able to offset their plant functional traits, typically associated with slow-growing grasses, with some demographic parameter like higher tiller population density, allowing it to be as productive as the fast-growing A. elatius when both were grown in fertile soil. Therefore, we suggest cautionary use of traditional plant functional traits to explain and predict the annual productivity of slow-growing grasses.

Fatty acid profile in vertical strata of elephant grass subjected to intermittent stocking

ABSTRACT The milk and meat from animals with a pasture-based diet have higher proportions of CLA and C18:3 and lower omega-6:omega-3 ratios than products from animals with diets based on corn silage and concentrate. However, most of the published studies have evaluated fatty acid profiles in temperate climate grasses and the literature with tropical grasses is scarce. Thus, the aim of this study was to evaluate the morphological and fatty acid compositions in the vertical strata of elephant grass (Pennisetum purpureum Schum.) swards subjected to grazing heights (90 or 120 cm pre-grazing heights) and levels of defoliation (50% or 70% removal of the initial pre-grazing height). There were no interactions among pre-grazing height, the level of defoliation and grazing stratum. However, higher proportion of C18:3 (58% and 63%) was found in the 90-cm swards and in the half upper stratum. A higher proportion of C18:3 was associated with a higher leaf proportion and crude protein content. Thus, the upper stratum of sward or a grazing management scheme (e.g. first-last stocking) resulting in a higher proportion of leaves and crude protein both provide higher proportions of C18:3 to animals grazing in elephant grass swards.

Fatty acid profile in vertical strata of elephant grass subjected to intermittent stocking.

The milk and meat from animals with a pasture-based diet have higher proportions of CLA and C18:3 and lower omega-6:omega-3 ratios than products from animals with diets based on corn silage and concentrate. However, most of the published studies have evaluated fatty acid profiles in temperate climate grasses and the literature with tropical grasses is scarce. Thus, the aim of this study was to evaluate the morphological and fatty acid compositions in the vertical strata of elephant grass (Pennisetum purpureum Schum.) swards subjected to grazing heights (90 or 120 cm pre-grazing heights) and levels of defoliation (50% or 70% removal of the initial pre-grazing height). There were no interactions among pre-grazing height, the level of defoliation and grazing stratum. However, higher proportion of C18:3 (58% and 63%) was found in the 90-cm swards and in the half upper stratum. A higher proportion of C18:3 was associated with a higher leaf proportion and crude protein content. Thus, the upper stratum of sward or a grazing management scheme (e.g. first-last stocking) resulting in a higher proportion of leaves and crude protein both provide higher proportions of C18:3 to animals grazing in elephant grass swards.