Emergência e crescimento inicial de plantas de girassol sob excesso hídrico

Abstract

The sunflower cultivation has great potential for success in different edaphoclimatic regions. However, the stress occurrence, including the water excess on soil is detrimental to the crop development and production. The aim of this study was to determine the initial development stages wherein water excess and its duration affect longer negatively the emergence and early growth of sunflower plants. The experiments were carried out in the experimental area of Departamento de Fitotecnia of UFSM, during the second half of 2011. Three experiments were carried out under greenhouse and a field experiment. The experiments under greenhouse were carried out in pots, with treatments based on the application of water excess at different stages of development (at sowing date, three days after sowing, emergency date, V2 and V4 stage) combined with different durations (0, 48, 96, 144, 192 and 240 hours), in a completely randomized design, bifactorial. We determined the following variables: percentage and speed of emergency after emergency stabilization; dry mass of shoots and roots, leaf area, plant height, leaf number, maximum length of roots and main length root, and some growth index, determined after the end of application the last treatment of water excess. The field experiment was carried out in a completely randomized design, consisting of weekly sowing made between 28/07/2011 and 27/11/2011, which occurred in different conditions of excess water, soil temperature and soil moisture. Soil temperature was monitored by Pt-100 sensors, while excess water and soil moisture were determined by sequential water balance, which were correlated with the percentage of emergence, speed emergence and number of days of the phase sowing-emergency. It was found that the water excess is more detrimental for sunflower in phase sowing-emergence, because it affects negatively the emergence and consequently the plants density, reducing the growth of shoots and roots significantly, even after just 48 hours under water excess. Applied after emergence, the water excess causes significant reduction of shoot growth, while in the soil occurs development of adventitious and secondary roots. Both water excess as water deficit is detrimental to the field emergency, because soil moisture between 80 and 85% of the soil storage capacity and soil temperature of 21.5 °C are the best conditions to sunflower emergence.