Azevém submetido à frequência de desfolha e níveis de adubação nitrogenada em solos de várzea

Abstract

Several studies are made in Rio Grande do Sul relative to livestock on annual ryegrass pasture (Lolium multiflorum Lam.) and this shows the importance of this sort of production system in the south of Brazil. However of this, the objective of this work is to evaluate the ryegrass subjected to a defoliation frequency and nitrogen fertilizers levels in the western border of Rio Grande do Sul. The trial wastaken in the experimental area of Universidade Federal do Pampa, in a Plinthaquox soil type. The study consisted in the evoluation of tetraploid ryegrass cultivate Barjumbo as the number of leaves per plant (NA), tillers density per m² (DA), number of leaves per plant (NF), height (ALT), air length (CPA), production of dry biomass (MS), culm/leaf ratio (REL), and leaf area (AF), with the utilization of 2 factors, being the main factor the frequency of defoliation in (0,1, 2 and 3 cuts) and the other factor: two levels of nitrogen fertilization: (100 and 200 kg de N ha-¹), in an experimental design completely randomized in a factorial arrangement 4 x 2, with three repetitions. The sowing happened on may 4th, 2011, putting in portions of 1,5 x 2 m, with the seed density corresponding to 1,5 kg ha-¹, after the pH coorection and phosphorus and potassium soil fertilizer. The nitrogen fertilizer was fragmented four times, being applied 1/3 of N, in urea way, in base and the rest (2/3) fragmented also in each 28 days. During the trial it was done evaluations to these variables: NA, DA, NF, ALT, CPA, and MS, and statistical analysis to REL, and AF. For the factor of frequency of defoliation, the development characteristics, only a variable ALT showed significant difference (P<0,05), and being the treatment without defoliation the best average. For the same characteristics the greatest amount of fertilizing (200 kg N ha-¹) made a positive effect only for variables NA and ALT, for the others the increase in the nitrogen amount don’t made effect. For the variables of production the cut factor (defoliation) showed difference in the variable MS and REL. For the fertilizer factor XI there was a significant difference only in REL, being extremely harmful the absorption of forage. It follows that is possible higher defoliation frequency to this cultivate, and nitrogen from 100 to 200 kg N ha-¹ is not recommended, because don’t bring any benefits to the main variables of development and production.