The influence of soil compaction and conservation tillage on sunflower's (Helianthus annuus L.) below ground system

Soil compaction represents an important issue in the actual context of agricultural system sustainability. Research on the various developments of root systems under tillage has been explored for many crops, whether for the biomass area or the underground, but very little concerns Sunflower (Helianthus annuus L.). The objectives of the study were to understand the impact of soil tillage and of the induced mechanically compacted soil on: i) sunflower's root system architecture, ii) biomass area iii) production. Two complementary experiments were realized in the south of France (France's main sunflower production area). In both experiments, increased resistance of the soil to penetration was observed, characterizing soil compaction. Under compacted soil, major changes in the sunflower's root architecture occurred (-55% of root length, -67% of root surface, and -42% of root diameter) and root system exploration was negatively impacted (assessed through the use of semivariogram). This resulted in a decrease of deep root exploration and in an increased lateral growth. Modifications of leaf surface, biomass, yield, and kernel components were also reported. Those modifications were the consequences of soil compaction, and suggest a compensatory effect under such constraint.