ABSTRACT: Sunflower crops are grown in different regions worldwide. However, the stress caused by water excess in the soil impairs this crop growth and yield. The aim of the present study was to determine the response of sunflower plants to long periods of water excess during initial development stages. Water excess treatments were applied at the initial development of these plants at the sowing day, three days after sowing, at plant emergence, and at V2 and V4 stages. The treatments had different duration periods (0, 48, 96, 144, 192, and 240 hours) and were applied at three sowing dates. The current experiment is factorial and was carried out according to a completely random design. Two plant pots, treated under greenhouse conditions, made up the experimental units. Plant emergence, leaf area, plant height, shoot dry mass, maximum root length, main root length and root dry mass were herein assessed. Water excess is more harmful to sunflower plants during the sowing-emergence period. It substantially reduces emergence, plant density, shoot and root growth, even after 48-hour stress. Moreover, water excess leads to the formation of adventitious and secondary roots.

O girassol (Helianthus annuus L.) é uma cultura oleaginosa que pode ser cultivada em diferentes regiões e épocas de semeadura, porém nem todas as regiões e épocas de semeadura são apropriadas para o desenvolvimento da cultura. O objetivo deste trabalho foi determinar as características de crescimento e produtividade do girassol em sete datas de semeadura, em Santa Maria, de 2007 até 2012. Cinco experimentos foram conduzidos em um delineamento fatorial inteiramente casualizado com quatro repetições. O fator "A" foram datas de semeadura mensais do início de agosto até fevereiro e o fator "D" foram dois híbridos de girassol. Diâmetro de capítulo, índice de área foliar máximo, altura máxima de ??plantas, massa de mil aquênios, e produtividade foram determinados. Em anos normais ou de La Niña a maior produtividade é obtida nas semeaduras de setembro, enquanto que em anos de El Niño, o crescimento e a produtividade da cultura em semeaduras precoces são afetadas negativamente, devido à elevada precipitação pluvial, excesso hídrico no solo e doenças.

Sunflower (Helianthus annuus L.) is an oilseed crop that can be grown in different regions and sowing dates, but not all regions and sowing dates are appropriate for the crop development. The aim of this study was to determine yield and growth characteristics of sunflower on seven sowing dates, in Santa Maria, from 2007 to 2012. Five experiments were carried out in a completely randomized factorial design with four replications. The factor "A" was monthly sowing dates from the beginning of August to February and the factor "D" was two sunflower hybrids. Capitulum diameter, maximum leaf area index, maximum height of plants, weight of thousand achenes and yield were determined. In normal or La Niña years the highest yield is reached in September sowing dates, while in El Niño years, the crop growth and yield in early sowings are affected negatively, due to heavy rainfall, soil water excess and plant diseases.

Objetivou-se com este trabalho a obtenção de modelos para a estimativa do saldo de radiação (Q*) a partir da radiação solar global incidente (Rg) sobre dosseis de plantas de girassol. Os experimentos foram conduzidos na área experimental da Universidade Federal de Santa Maria, nos anos de 2007, 2008 e 2009. O Q* foi medido com saldos radiômetros instalados acima das plantas e a Rg em estações meteorológicas automáticas. Para fins de cálculo foram efetuadas as somas diárias de Q* e de Rg, obtendo-se a relação entre Q* e Rg para cada dia. Obtiveram-se, então, modelos com elevado coeficiente de determinação e baixo RQME no teste entre valores medidos e estimados de um banco de dados independente, indicando precisão na estimativa do saldo de radiação em dosseis de girassol, independendo da época de cultivo no ano. A função linear geral obtida com dados de diferentes épocas de cultivo foi: Q* = 0,5285 Rg (R² = 0,95), que no teste apresentou RQME = 1,04 MJ m-2 d-1. Conclui-se que o saldo de radiação (Q*) pode ser estimado utilizando-se a radiação solar global medida em estações automáticas, com precisão suficiente para os diferentes fins na agrometeorologia do girassol.

This study aimed to develop models for estimating the net radiation (Q *) from the incident solar radiation (Rg) on canopies of sunflower plants. The experiments were conducted at the Plant Science Department of the Federal University of Santa Maria in 2007, 2008 and 2009 years. Q* was measured by net radiometers above the plants and Rg by automatic weather stations. For purposes of calculation, daily sums of Q* and Rg were performed, obtaining the relationship between Q* and Rg for each day. Models with high coefficient of determination and low RQME were obtained in test between measured and estimated values from an independent database, indicating precision to estimate net radiation in sunflower canopies, regardless of cultivation time in year. The general linear function with data obtained from different times of cultivation was: Q* = 0.5285 Rg (R² = 0.95), that the test showed RQME = 1.04 MJ m-2 d-1. It was concluded that net radiation (Q*) can be estimated using solar radiation measured by an automatic stations with sufficient accuracy for different purposes in sunflower agrometeorology.