Growth and production of ornamental sunflower grown in the field in response to application of humic acids

The humic acid fraction of organic matter has a stimulating effect on the growth and development of ornamental plants. This study investigated the response in growth and yield of field-grown ornamental sunflower (Helianthus annuus L.) to the seed treatment with humic acids. The experiment was arranged in a randomized block design with three replications. Sunflower seeds were soaked in solutions of 0, 10, 20, 30, and 40mmol [L.sup.-1] C in the form of humic acids and then sown in the flower beds. At harvest, the flower stems were collected to determine the variables: stem height, stem diameter, fresh stem weight, number of leaves per stem, leaf fresh weight per stem, leaf dry matter per stem, number of flower stalks, and diameter of the floral receptacle. Data were subjected to regression analysis. The results showed increases in all variables in response to the application of humic acids, except in number of leaves per stem, which remained unchanged. The greatest increases usually resulted from concentrations from 15 to 20mmol [L.sup.-1] C in the form of humic acid. It was concluded that the seed treatment with humic acid at the indicated concentrations increases the number and commercial quality of flower stalks of field-grown ornamental sunflower.Os acidos humicos, fracao da materia organica, apresentam efeitos estimulantes no crescimento e desenvolvimento de plantas ornamentais. O presente trabalho objetivou estudar o crescimento eproducao de girassol ornamental (Helianthus annuus L.) em resposta a aplicacao de acidos humicos em cultivo em campo. O delineamento estatistico foi o de blocos casualizados com tres repeticoes. As sementes foram imersas nas solucoes de 0, 10, 20, 30 e 40mmol [L.sup.-1] de C na forma de acidos humicos e, posteriormente, semeadas em canteiros a campo. No momento da colheita, as hastes florais foram coletadas para medicao das variaveis: altura da haste, diametro da haste, materia fresca da haste, numero de folhas por haste, materia fresca foliar por haste, materia seca foliar por haste, numero de hastes florais e diametro do receptaculo floral. Os dados foram submetidos a analise de regressao. Os resultados mostraram incrementos em todas as variaveis analisadas, em resposta a aplicacao de acidos humicos, com excecao do numero de folhas por haste, que nao sofreu alteracao. Os maiores incrementos foram, em geral, proporcionados em concentracoes entre 15 a 20mmol [L.sup.-1] de C na forma de acidos humicos. Conclui-se que o uso dos acidos humicos nas concentracoes indicadas aumenta o numero e a qualidade comercial das hastes florais de girassol ornamental cultivado em campo