-In general, lodging has been controlled by restricting nitrogen fertilizer application and/or using short cultivars. Growth retardants can also be used to solve this problem.The objective of this study was to evaluate the effect of rates and application times of three growth retardants on Pioneiro wheat cultivar. The trial was carried out in Viçosa-MG, from May to September 2005, in a factorial and hierarchical scheme, in a randomized block design with four replications and a control treatment. The treatments consisted of 500, 1,000 and 1,500 g ha -1 of chlormequat; 62.5, 125 and 187.5 g ha -1 of trinexapacethyl and 40, 80 and 120 g ha -1 of paclobutrazol applied at growth stages 6 or 8, growth stage used on the scale of Feeks and Large, and a control treatment without growth retardant application. Only trinexapac-ethyl and chlormequat were efficient in reducing plant height; the effect of chlormequat and paclobutrazol on plant height was independent of the application time, but the trinexapac-ethyl at growth stage 8 produced shorter plant height than at stage 6. Increasing growth retardant rates produced shorter plant heights; chlormequat and paclobutrazol did not affect grain yield. However, the highest trinexapac-ethyl rates reduced wheat yield.

RESUMOObjetivou-se avaliar o efeito de doses e formas de aplicação de nitrogênio sobre o desempenho e produção de duas cultivares de trigo. O experimento, conduzido em Viçosa-MG, de maio a setembro de 2005, foi instalado segundo um esquema fatorial 2x2x5 no delineamento de blocos casualizados, com quatro repetições. Os tratamentos avaliados consistiram da combinação das cultivares de trigo, BRS 210 e Pioneiro, duas formas de aplicação de adubo nitrogenado (dose total aplicada por ocasião da semeadura ou 20 kg ha -1 na semeadura e o restante em cobertura no início da fase de perfilhamento) e cinco doses de nitrogênio (40, 60, 80, 100 e 120 kg ha -1 ) tendo como fonte o sulfato de amônio. A cultivar Pioneiro apresentou maior potencial produtivo que a cultivar BRS 210, mas foi menos resistente ao acamamento. O parcelamento da adubação nitrogenada proporcionou maior acamamento e não trouxe benefícios à produtividade dos grãos. As doses de N promoveram resposta quadrática da produtividade dos grãos, com ponto de máxima estimado na dose de 96,8 kg ha -1 e, aumento linear do acamamento de plantas da cultivar Pioneiro. Termos para indexação:Triticum aestivum, adubação nitrogenada, acamamento, produtividade. ABSTRACTThe objective of this work was to evaluate the effect of doses and methods of nitrogen application on the development and yield of two wheat cultivars. The experiment was conducted in Viçosa-MG, from May to September 2005, and it was arranged in a 2x2x5 factorial, randomized block design with four repetitions. The treatments consisted of the combination of the two wheat cultivars, BRS 210 and Pioneiro, two nitrogen application methods (total dose applied at seed sowing or 20 kg ha -1 at sowing and the remaining as topdressing in the beginning of tillage) and five N doses (40, 60, 80, 100 and 120 kg ha -1 ) with ammonium sulfate as N source. Cultivar Pioneiro showed higher yield potential than cultivar BRS 210, but it was less resistance to lodging. Splitting nitrogen fertilization increased lodging and brought no benefit to grain yield. Grain yield response to N doses was quadratic, reaching maximum at 96.8 kg ha -1 , and linear increase in lodging of cultivar Pioneiro plants.

RESUMO. Objetivou-se com este trabalho avaliar o efeito de doses e épocas de aplicação de três reguladores de crescimento na elongação do colmo de plantas de trigo. O experimento, conduzido em Viçosa, Estado de Minas Gerais, de maio a setembro de 2005, foi instalado com tratamentos em esquema fatorial e hierárquico com uma testemunha, no delineamento em blocos casualizados com quatro repetições. Os tratamentos foram 500; 1.000 e 1.500 g ha -1 de clormequat; 62,5; 125,0 e 187,5 g ha -1 de trinexapac-etil e 40; 80 e 120 g ha -1 de paclobutrazol, aplicados no estádio 6 ou 8 da escala Feeks e Large, e uma testemunha. O comprimento do colmo com trinexapac-etil foi menor do que com o clormequat, que, por sua vez, foi menor do que com o paclobutrazol. A aplicação de reguladores na época 1 promoveu maior redução dos entrenós basais, enquanto a aplicação na época 2 proporcionou maior influência no pedúnculo. O aumento das doses de clormequat e trinexapac-etil promoveu redução do comprimento do colmo e das partes que o formam. O aumento das doses de paclobutrazol promoveu respostas pouco expressivas no colmo e seus componentes. Palavras-chave:Triticum aestivum L., clormequat, trinexapac-etil, paclobutrazol. ABSTRACT. Effect of growth regulators on wheat stem elongation.The objective of this work was to evaluate the effect of doses and times of application of three growth regulators on wheat stem elongation. The experiments were conducted in Viçosa, Minas Gerais State, from May to September 2005, in a factorial and hierarchical randomized block design with four repetitions and a control treatment. Treatments consisted of 500, 1000 and 1500 g ha -1 of chlormequat; 62.5, 125.0 and 187.5 g ha -1 of trinexapac-ethyl and 40, 80 and 120 g ha -1 of paclobutrazol, applied either at the 6 or 8 stage of the Feeks and Large scale, with a control. Stem length with trinexapac-ethyl was smaller than with chlormequat, which was in its turn smaller than with paclobutrazol. Application of growth regulators at stage 1 produced shorter basal internodes, whereas the stage 2 application caused greater reduction in the peduncle. The increase in chlormequat and trinexapac-ethyl doses reduced length of stem and its parts. The increase in paclobutrazol doses had very small effects on wheat growth and its parts.

Urea is one of the most used nitrogen fertilizers worldwide.