Title: Nitrogen Nutrition Index in perennial winter pastures grown as monocultures or intercropped.

 

Abstract: Nitrogen (N) participates in several metabolic processes in the plant and is directly related to the accumulation of dry matter of the pasture, thus reflecting increases in the overall productivity of the system. In this sense, the Ncritical (lower concentration of N for a given species to perform its maximum growth potential) in multispecies pastures may change depending on the species that compose it. The objective of this work was to evaluate the NNI (Nitrogen Nutrition Index) in three perennial winter grasses (oatgrass - Arrhenatherum elatius, cocksfoot - Dactylis glomerata - and tall fescue - Festuca arundinacea) cultivated as monocultures or intercropped throughout the four seasons of the year. The experimental area was located in Lages, SC, containing 12 paddocks of 45 m2 each where the four treatments (the three pure cultivated species and the mixture) were distributed through a completely randomized design with three replicates. The cut height at each treatment was determined by the time the swards intercept 95% of the incident light during the vegetative stage of the pastures, being lowered by 50% of this height. Fertilization was carried out with the equivalent of 50 kg / N / ha every 40 days, totaling 450 kg of N / ha / year. The forage mass was determined in pre-cut, and thus evaluated the N contents in the forage mass and the N contents in the 10 cm of the upper part of the canopy for the species pure and individually for each species in the consortium. The Ncritical was estimated by the equation: Ncritical = 4,8 x W0,32, where W is the mass of forage above the level of the soil. A second experiment was carried out with the objective of evaluating the effect of the management adopted on the N dilution curve, in which two methods were performed to determine the N dilution curve, one performed with the management adopted in the experiment (starting from a residual height of 10 cm) and another with the management proposed by the literature starting from the ground level. Statistical analyzes were performed using the MIXED procedure of the SAS statistical program (version 9.02) with 5% significance. Regression analyzes were performed using the SigmaPlot(R) statistical package. In general, the NNI actually observed did not reach the critical values (Experiment I), however, when corrected (disregarded the percentage of dead material in the sample) NNIs were satisfactory for all species at all times. Throughout the manuscript inferences are discussed on the ways to evaluate the INN in perennial pastures under lenient grazing, due to the changes in the dilution of nitrogen, due to the high percentage of dead material at the beginning of pasture growth. The height control was important in the coexistence of the species in the consortium, since it allowed the entrance of luminosity, decisive factor in the absorption of N.

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Keywords: Species mixture; nitrogen content; nutrition status; dilution curve.

 

Author: Luana Fidelis Américo

Leader: André Fischer Sbrissia

Dissertation (Masters in Animal Science)

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Title: Tillering demography and population stability of Capim-caninha in natural pastures submitted to different heights.  

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Abstract: Since the establishment of livestock farming in the southern Brasil, the main component of the herbivorous diet are the native pastures. However, the low productivity and economic profitability of these areas makes the producer opt to invest in other agricultural products that stand out in the current market. In order to be able to increase gains in a sustainable way, a greater technical knowledge is required, regarding the response patterns and growth physiology of the predominant species in natural pasture. Thus, the objective of this work was to evaluate the stability of the tiller population of the predominant species (Andropogon lateralis Nees – capim caninha) in a native pasture submitted to management strategies. The experiment was conducted in an area belonging to the Agricultural Research and Rural Extension Company of Santa Catarina (EPAGRI / Lages) with four treatments and four replicates in 16 paddocks of 875 m² each in a randomized complete block design. The treatments consisted of four pre- grazing heights (12, 20, 28 and 36 cm - targets based on capim-caninha), which were lowered in the same proportion of defoliation of 40% of the initial height. With the use of the technique of marked tillers, the dynamics of appearance and death of tillers were evaluated over 18 months. Data were submitted to analysis of variance (P <0.05), using SAS statistical program. The results indicated that the use of different management heights in the native pasture does not affect the stability of the tiller population of the predominant species (Andropogon lateralis) and that, regardless of the management used, the persistence pathway of that species is mainly based on maintenance of high tillering survival rates.

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Keywords: Native pastures; Stability, Management, Tillering.

 

Author: Luis Henrique Paim Della Giustina Junior

Leader: André Fischer Sbrissia

Dissertation (Master in Plant Production)