Title: Tillering and accumulation dynamics in pastures of oat and ryegrass cultivated pure or intercropping

 

Abstract: In regions with subtropical climates the use of grasses intercropping, mainly oats and ryegrass is a common practice, but the advantages and disadvantages of the intercrop in relation the pure culture are little studied. The aim of this work was to evaluate the production and persistence of black oat and ryegrass swards grown pure or intercropping throughout the period of use. The three treatments were randomly distributed into a complete blocks design with four replicates. The pre-grazing sward heights were 23, 20 and 17 cm for the oat, intercrop and ryegrass treatments, respectively. The post-grazing sward heights were 40% lower than their initial heights. Morphogenesis was performed using the technique of marked tillers and dynamic and tiller population density (TPD) was determined with three 10-cmdiameter PVC rings per paddock. The treatments did not differ in the final length of intact leaf, being the October month with the lowest values (approximately 48% lower). The phyllochron was not affected by the form of cultivation, but the values were increasing with the advance of the growing season. The leaf elongation rate decreased over the months, with a mean value of 0.14 cm / perfilhos.graus-day for all treatments. The advance of the growing season resulted in increases stem elongation rates, with the species in the intercrop having smaller increments in the final months. In general, rates of senescence reduced with the advance of months, and the intercrop increased tissue death of ryegrass. The intercrop TPD remained constant until October, inverting the participation of species in August. Of the tillers existing on the last grazing cycle, approximately 0, 40 and 20% were first generation of the oats, ryegrass and intercrop, respectively. Thus, despite of ryegrass pure have the lowest rate of tillering, it have the same rate of population stability of the intercrop. The pure ryegrass had the highest average net accumulation rates by offering smaller forage losses by senescence. 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. For the species tested the developmental stage of sward has greater influence on the morphogenesis and structural characteristics than cultivation form. The morphological similarity of oats and ryegrass enables evaluated traits similar in both forms of cultivation. When intercropping the temperate climate grasses under rotational grazing, size/density compensation mechanisms occurred throughout the grazing cycles and in the plant communities the same form of the pure cultivation to maintain the leaf area index and production capacities of the pastures.

 

Keywords: Avena Strigosa Schreb cv. IAPAR-61, competition, Lolium multiflorum Lam. cv. Comum, morphogenesis, population dynamic, self thinning rule

 

Author: Paulo Gonçalves Duchini

Leader: André Fischer Sbrissia

Dissertation (Masters in Animal Science)

 

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Title: Frequency and severity of defoliation in pastures of Brachiaria humidicola submited to continuous stocking

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Abstract: The grazing efficieny is directly related to defoliations events occurring in individual leaves and tillers. Independent of grazing method (continuous stoking, rotational stocking and strip grazing) the patterns of defoliation is affected by stocking density that is closely associated with the growth rate of pastures. Thus the aim of this study was determine the leaf area index (LAI) and defoliation patterns in individual tiller characterized by the frequency and severity of defoliation and its implications on the efficiency of grazing in pastures Brachiaria humidicola cv. Comum under continuous stocking during the dry season of the year. The experiment was conducted at Embrapa Beef Cattle, 20°27’ S, 54°37’ W and 530 m altitude, Campo Grande, MS, in the period of April-October 2012. The treatments consisted of maintaining two management criterium of B. humidicola cv. Comum under continuous stocking characterized by a range of 10 – 15 and 20 – 25 cm of sward surface height. The experiment was conducted according a complete randomized block design with three replications. The experimental area of 4,5 ha was divided into six experimental units (paddocks) of 0,75 ha. The LAI of each treatment was obtained by the product of mean leaf area of each tiller by tiller population density. To evaluate the frequency and severity of defoliation 15 tillers were selected within each experimental unit whose frequency and duration of the evaluation cycle were dependent on the growth rate of pastures (frequency evaluation of three and four days and cycle of collection of 28 days for the months of april and may, and frequency of 10-day evaluation and collection cycle duration of weeks for the months june, july, august, september and october). The evaluation consisted of: LAI, frequency of defoliation of individual tillers and leaves, defoliation frequency by category of leaf, severity defoliation by leaf, severity of defoliation by category leaf and grazing efficiency. The LAI was similar between managements targets, despite the existence of contrasting heights. The stocking density did not differ significantly between height ranges, resulting in the similarity of the frequency of defoliation of individual tillers and leaves. Higher swards had a more severe defoliation of leaves. Regarding the time of year, generally the severity of defoliation was antagonist to defoliation frequency so that the period which occurred less frequently defoliation of leaves and tillers was observed more severe defoliation of them, resulting in higher grazing efficiency. Thus, in times of the year where the growth factors are limiting (water stress, reduction in luminosity and temperature), swards heights does not seem be a good predictor of frequency and severity of defoliation of individual tillers in pastures under continuous stocking.

 

Keywords: Tiller density; Height ranges of management; LAI

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Author: Tiago Miqueloto

Leader: André Fischer Sbrissia

Dissertation (Masters in Animal Science)

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Title:  Acúmulo de forragem e composição química em pastos de capim-quicuiu submetidos a estratégias de lotação intermitente

Acúmulo de forragem e composição química em pastos de capim-quicuiu submetidos a estratégias de lotação intermitente

 

Author: Deisy Andrade Padilha

Leader: André Fischer Sbrissia

Dissertation (Masters in Animal Science)

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