Title: Forage accumulation and population stability in mixed pastures composed of Cenchrus clandestinus and Lolium arundinaceum

 

Abstract: The use of different species to create a diverse pastoral environment has gained attention because of the productive, economic, and ecological benefits provided. Grasses play an important role as constituents of this diversity because of their greater productive capacity and greater forage accumulation. In temperate climates, mixed cultivation of species from tropical and temperate climates is possible; however, management acts as a modulator of the ontogenic processes of pasture growth and persistence. The objective of this study was to determine a management strategy for mixed pastures formed by Cenchrus clandestinus and Lolium arundinaceum that allows increases in annual forage production and guarantees population stability of the species in the mixture. An experimental protocol was conducted in a 2 × 2 factorial arrangement, with three replications, where factor A represents the management heights:15 and 20 cm in pre-grazing (defoliation severity of 40%), and factor B indicates the presence or absence of a single management of pasture to 6 cm in mid-spring. The pasture was composed of L. arundinaceum (a temperate climate species) and C. clandestinus (a tropical climate species) established in 2014. From November 2017 to November 2020, samples were collected in tables for each grazing cycle. metal plates of 0.24 m² of area to estimate the botanical constituents of the pasture and measured the pre- and post-grazing mass using the Rising Plate Meter to estimate forage accumulation, with its own calibration. The emerged and surviving tillers were identified and counted monthly in two PVC rings with a radius of 10 cm, allocated to each experimental unit. The data were grouped into growth periods and subjected to the F test, with means estimated by SAS LSMEANS and tested using the Tukey test at 5% significance. There was no effect of year on forage accumulation; however, height and spring management had an effect. Pastures managed at 20 cm or those subjected to severe defoliation in the spring have a greater annual accumulation of forage. L. arundinaceum and C. clandestinus are complementary in their demographic patterns and coexist harmoniously over time. Managing pastures at 20 cm in pre-grazing associated with spring management favors the early return of C. clandestinus in spring and increases the nitrogen nutrition index of L. arundinaceum in summer by replacing old tillers with new tillers and increasing the DPP of L. arundinaceum in winter. Our results suggest that the combination of the perennial species L. arundinaceum and C. clandestinus in pastoral environments is possible and viable. However, one must opt for pre-grazing pasture management at a height of 20 cm, using strategic spring management that combines a greater balance in population patterns and greater productivity. Pastures managed at 15 cm favor the occurrence of invasive plants and allow for less forage accumulation, as they enter at a management height lower than the management flexibility of L. arundinaceum.

 

Keywords: grazing management; plants coexistence; tall fescue; kikuyu grass.

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Author: Fábio Luís Winter

Leader: André Fischer Sbrissia

Thesis (Doctors in Animal Science)

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Title: Herbage production and vegetation dynamics of multispecies pastures managed at two pre-grazing canopy heights and three nitrogen fertilization rates

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Abstract: The establishment of pastoral environments with functionally distinct plants has been considered an important tool for the sustainable intensification of productive systems. However, the challenge of these systems is the preservation of species diversity over time. The objective of this work was to determine management strategies that combine species diversity and forage production in a multispecific pasture composed by grasses and legumes and to identify whether the management adopted during the warm season promotes an effect on vegetation dynamics in the pasture growth in subsequent cool season. For this, an experimental area was formed with the species Arachis pintoi, Cenchrus clandestinus, Cynodon spp., Lotus corniculatus L. and Trifolium repens L., and sown Lolium multiflorum L. in the cool season. The experiment design was a complete randomized block design, assigned in a 2x3 factorial arrangement with three replications per treatment. The treatments were two pregrazing heights, 17 and 23 cm, associated with three rates of nitrogen fertilization, 50, 150 and 250 kg of N ha-1. This management was adopted during the warm season of 2020, 2021 and 2022 (November to April), while in the cool season of the same years (May to October), the management was the same for all treatments, with pre-grazing height of 20 cm associated with a single fertilization with 50 kg of N ha-1. The stocking method in both seasons was intermittent with the target post-grazing height corresponding to 60% of the pre-grazing height. There was no effect of management height on forage production in the warm season, while rates of 150 and 250 kg of N ha-1 increased forage production, but decreased species diversity, mainly of legumes, compared to the 50 kg of N ha-1 rates. The species Cenchrus clandestinus and Cynodon spp. corresponded to around 85% the canopy during the warm season and coexisted in similar proportions regardless of management. In the cool season, forage production was similar regardless of the N rate applied in summer, while species diversity was lower when pastures were managed with heights of 17 cm in summer, with a significant reduction in the percentage of Lotus corniculatus L. in the mixture. Our findings suggest that in mixed pastures composed by grasses and legumes, a supply of N in the summer that maintain the grasses in a nitrogen nutrition status from 0.8 to 1.0 reduces species diversity in the canopy and does not affect forage production in the following cool season. In addition, managing a mixture at a height close to the upper limit of management height corresponding to the critical LAI is an alternative to attenuate the loss of species diversity, without compromising forage production.

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Keywords: ecosystem services, functional diversity, multifunctionality, multispecific pastures, plants coexistence.

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Author: Daniel Augusto Barreta

Leader: André Fischer Sbrissia

Thesis (Doctors in Animal Science)