Teor de proteínas nos grãos em resposta à aplicação de nitrogênio em diferentes estádios de desenvolvimento da cevada Protein content in barley seeds affected by nitrogen application in different growth stages

O presente trabalho teve como objetivo avaliar o teor de proteínas em grãos de cevada em resposta à aplicação de N em estádios de desenvolvimento da cultura. Os experimentos foram conduzidos em Eldorado do Sul e Encruzilhada do Sul, no ano de 2000, e em Victor Graeff, nos anos de 2000 e 2001, em delineamento experimental em blocos casualizados com quatro repetições. Os estádios de aplicação de N foram na emergência das plântulas; na emissão da 2&ordf; ou 3&ordf; folha; da 4&ordf; ou 5&ordf; folha; 6&ordf; ou 7&ordf; folha; 8&ordf; ou 9&ordf; folha; e no emborrachamento. As doses de N foram de 30 ou 40kg ha-1 e 60 ou 80kg ha-1, para a menor e maior dose, respectivamente. As determinações realizadas foram teor de proteínas nos grãos e número de grãos metro-2. Para os experimentos realizados em 2000, a aplicação de nitrogênio até o início do alongamento dos entrenós (emissão da 7&ordf; folha) manteve o teor de proteínas no grão abaixo dos 12%, mesmo para a maior dose de N. Os teores de proteínas no grão em Victor Graeff, no ano de 2001, ficaram acima do limite máximo de 12% com a aplicação da maior dose de N já em estádios iniciais de desenvolvimento da cultura, devido ao maior teor de matéria orgânica no solo em relação aos outros locais.<br>This study was was aimed at evaluating the protein content in barley seeds affected by nitrogen application in different growth stages. Experiments were carried out in Eldorado do Sul and Encruzilhada do Sul, in 2000, and Victor Graeff, in 2000 and 2001, on a randomized blocks scheme with four repetitions. The growth stages of N application were in emergency of seedlings; emission of 2nd or 3rd leaf; 4th or 5th leaf; 6th or 7th leaf; 8th or 9th leaf; and in boot stage. The N rates were 30 or 40kg ha-1 and 60 or 80kg ha-1, for smallest and largest N rate, respectively. The protein content in barley seeds and the number of grains area-1 were determined. In the experiments carried out in 2000 the nitrogen application until the beginning of the internodes elongation maintained the seeds protein content below of 12%, inclusive in the largest N rate. The seeds protein content in Victor Graeff, 2001, surpassed the maximum limit of 12% with N applications in initial growth stages, decurrently of the higher soil organic matter content in relation to others experiments

Root anchorage and its significance for submerged plants in shallow lakes.

Submerged plants in shallow lakes are subject to pulling forces arising from waves, currents and grazing birds. Such forces can cause anchorage failure (mainly dislodgement of the root system) or breaking failure of the stems. Both lead to loss of fitness but uprooting is more damaging because many perennial species can replace broken shoot systems. We investigated 12 abundant species (Ceratophyllum demersum, Chara sp., Eleogiton fluitans, Elodea canadensis, Myriophyllum spicatum, Najas marina, Potamogeton natans, P. obtusifolius, P. pectinatus, P. pusillus, Utricularia vulgaris and Zannichellia palustris) in 28 shallow lakes in the UK and the Netherlands. We measured the anchorage and breaking strengths of individual plants of different sizes. Anchorage strength depends on the cohesive strength of the sediment and the size of the root system. The undrained shear-strength of sediments in shallow lakes varied more than 50-fold, but all were substantially weaker than terrestrial soils. Anchorage strength was modelled using the product of sediment cohesive strength and four measures of root-system size. A transformation of plan-form area (raising it to the power 2/3) that represented the hemispherical surface area of the root ball was consistently the best predictor of anchorage strength. Breaking strength was a linear function of stem cross-sectional area in all species. Breaking stresses were comparable with those of marine algae and non-lignified terrestrial plants. The results were used, in combination with plant allometric relationships, to predict the fates of four of the species when challenged with the largest waves likely to be encountered in a 10-year period, and the even greater forces exerted by grazing birds. We show that sediment strength and plant size determine whether plants break or uproot. A careful balance between investment in anchorage and in breakage resistance is needed to survive in the fluctuating physical environment of lakes. Pulling forces experienced by aquatic plants are distinct from the mainly bending forces on more rigid land plants. We provide the first theoretical and quantitative framework for understanding their effects. Anchorage failure associated with the soft sediments of eutrophic lakes is likely to be a factor in the loss of macrophyte communities and an important factor in their restoration