Title: Establishment of silage maize over perennial winter pastures and its impact on forage production and pasture diversity

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Abstract: This study evaluated the impact of corn overseeding for silage production in established perennial cool-season pastures (Zea mays L.) on pasture production and diversity in the Cfb climate region of Southern Brazil. Three treatments were implemented over a 12- month grazing experiment: Corn Overseeding in Perennial Pasture (C), Seasonal Deferment (D), and Year-Round Grazing (YRG). The study was conducted on a >7-yearold pasture predominantly composed of tall fescue (Festuca arundinacea Schreb.), orchardgrass (Dactylis glomerata L.), and clover (Trifolium spp.). The Corn Integration treatment yielded the highest annual biomass production (13,360.68 kg DM/ha), effectively addressing the summer forage deficit. However, this intensive production model also resulted in a significant grazing gap, similar to the Deferment treatment, highlighting a need for strategic management to ensure year-round forage availability. The plant diversity dynamics assessed using Hill numbers (q=0, q=1, q=2) revealed complex response patterns. The Corn treatment showed a significant recovery in plant diversity, achieving higher final Hill numbers (q=0: 5.0±0.3; q=1: 3.6±0.2; q=2: 3.2±0.1) compared to Year-Round Grazing (q=0: 4.2±0.2; q=1: 3.0±0.2; q=2: 2.65±0.1) and Deferment (q=0: 3.7±0.2; q=1: 2.7±0.1; q=2: 2.4±0.1). In contrast, the Seasonal Deferment treatment showed the lowest final diversity, likely because of competitive exclusion during the rest period. These results suggest that the disturbance from the corn cycle may have activated the soil seed bank, promoting an increase in plant diversity, which aligns with the Intermediate Disturbance Hypothesis. However, the long-term sustainability of this effect requires further investigation to understand the full impact on the pasture ecosystem. Corn integration in pastures has the potential to enhance biomass and diversity, but it requires careful management to mitigate the associated grazing gap and to ensure the long-term ecological balance of the pasture system.

 

Keywords: Integrated crop-livestock systems, plant diversity, soil seed bank, intermediate disturbance hypothesis

 

Author: Igor Rodrigues Waltrick

Leader: André Fischer Sbrissia

Dissertation (Masters in Animal Science)

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Title: Understanding the coexistence and productive dynamics of Cenchrus clandestinus and Cynodon spp. cultivated in association

 

Abstract: More diverse pasture ecosystems have shown to be a promising alternative to monocultures commonly used in livestock systems. The main production modulators in such pastures are grazing management and nitrogen fertilization, which are responsible for modifying the patterns of individual and community responses of plants. Thus, the objective of this study was to identify whether fertilization strategies and doses alter the functional patterns of plants and promote different contributions to forage accumulation in pastures composed mainly of Cynodon spp. and Cenchrus clandestinus. The pasture was formed by the species Arachis pintoi, Cenchus clandestinus, Cynodon spp., Lotus corniculatus L. and Trifolium repens L., superseded with Lolium multiflorum L. in the cool season. Experiment 1 followed a randomized block design with a 2x3 factorial arrangement, with three replicates per treatment. During the warm season, three nitrogen rates (50, 150 and 250 kg N. ha-1 ) and two pregrazing heights (23 and 17 cm, post-grazing) were used, and in the cool season, rates of 50 kg N. ha-1 and management of 20 cm (pre-grazing, with the same grazing severity) were used, with analysis of roots of the species of interest being performed. Experiment 2 followed a randomized complete block design in a 2x2 factorial arrangement with four replicates per treatment. The factors were: (1) fertilization carried out in the cool season, where doses of 50 and 150 kg of N were distributed and (2) nitrogen fertilization in the warm season, in which doses of 100 and 200 kg of N were used over the doses already mentioned, obtaining the following treatments: Low-Winter-Low-Summer (LWLS; 50 + 100 kg of N.ha-1 ), LowWinter-High-Summer (LWHS; 50 + 200 kg of N.ha-1 ), High-Winter-Low-Summer (HWLS; 150 + 100 N.ha-1 ) and High-Winter-High-Summer (HWHS; 150 + 200 kg of N.ha-1 ), totaling applications of 150, 250 and 350 kg N. ha-1 . year-1 . All experimental units were managed with a pre-grazing height of 20 cm, with 40% defoliation severity. Tiller population density was obtained from representative pasture samples and counting of individuals of each species. The tissue flow dynamics of C. clandestinus and Cynodon spp. was performed on 20 tillers (ten of each species) per experimental unit. Forage accumulation was calculated from the daily leaf expansion rate per tiller x tiller population density x g.cm-1 (conversion factor). Data were subjected to analysis of variance by the InfoStat statistical package, using the MIXED procedure and the means tested by the Fisher LSD test with 5% significance. There was no difference in forage accumulation between treatments, but different nitrogen fertilization strategies modulated the productive dynamics of the pasture, affecting the relative contribution of each species. C. clandestinus contributed more significantly in environments with greater fertilization in the cold season, this response being linked to its lower basal temperature. Thus, it was observed that differences between these species allowed their coexistence and effective contribution to forage accumulation, which was modulated by the fertilization strategies used.

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Keywords: Tifton 85. Kikuyu grass. Nitrogen fertilization strategies. Forage accumulation

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Author: Fernanda Cristina Schütz Gislon

Leader: André Fischer Sbrissia

Dissertation (Masters in Animal Science)

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