Hybrid maturity and plant population density to improve sunflower performance in Entre Rios, Argentina

Sunflower yield is sensitive to rain magnitude and distributions during the growing season. Adverse effects of drought or excess of water might be avoided or alleviated by using a specific sunflower hybrid and plant population density. This study was conducted to compare agronomic performance of early and late maturity sunflower hybrids growing at different plant population density (PPD). o Field experiments were carried out at Paraná (Entre Ríos, Argentina) during two growing seasons (2009-10 and 2010-11). Two sunflower hybrids, DOW MG60 (early maturity) and DOW MG2 (late maturity), were sown at three PPD (3, 6, and 9 plant m-2). Rain between crop emergency and first anthesis was 69% greater in 2009-10 than in 2010-11 (266 vs. 158 mm) accounting for greater leaf area index (p<0.0001). On the other hand, excess of rain and less radiation around flowering could be related to lower harvest index (HI) in 2009-10 (p= 0.0026). Grain yield was 48% greater in 2010-11 in respect to 2009-10 and, for both years, showed an optimal value when hybrids were grown at 6 plant m-2. Even though dry matter at flowering increased with hybrid maturity and PPD, comparable grain yield for hybrids and a grain yield reduction at high PPD (associated to lower HI; p<0.0004) highlight the role of both favorable post-flowering weather conditions and maintenance of functional canopy for sunflower yield determination. Hybrids responded in a different way to yearly weather conditions (year x hybrid interaction; p=0.0185). In spite of grain yield differences between hybrids (19% for 2009-10 and 10% for 2010-11), lack of significance does not allow to identify a specific combination between hybrid maturity and the weather condition of a specific year. Results suggest that exist an optimum PPD for sunflower growing at Entre Ríos and indicate that hybrid maturity do not alter sunflower agronomic performance. In order to increase yield potential, breeding should improve post-flowering partitioning and high PPD tolerance in late maturity hybrids.