Agronomic response of sunflower subjected to biochar and arbuscular mycorrhizal fungi application under drought conditions

Abstract

There is growing interest in developing environment-friendly farming practices that can limit the impact of drought stress in agriculture. The main objective of this study was to investigate the e combined effects of biochar and arbuscular mycorrhizal fungi (AMF) on the agronomic responses of sunflower. Field experiments were conducted in the 2018 and 2019 growing seasons in semi-arid environments of Iran. The following treatments were adopted: i) three levels of biochar [0, 2.5 and 5 t ha–1 of biochar called Bl, Bm and Bh, respectively]; and ii) three irrigation levels (50, 30 and 10% of the maximum available water (MAW) called 50MAW, 30MAW and 10MAW, respectively)]; iii) two levels of AMF inoculation (with and without the addition of AMF called+AMF and–AMF, respectively). The experimental design was a random-ized complete block design. At flowering, the leaf area index (LAI) was generally higher in the plants subjected to Bh-+AMF (on average 4.95), even if the LAI values changed according to biochar application (Bh > Bm > Bl) and the level of irrigation (50MAW > 30MAW > 10MAW). At harvesting, sunflower seed yield was highest in+AMF and in Bh (on average 53.9 and 51.2 g plants–1, respectively). Sunflower plants subjected to Bh-+AMF showed the highest seed yield under all irrigation levels (79.4, 57.1 and 32.3 g plant–1 in 50MAW, 30MAW and 10MAW, respective-ly). The application of biochar combined with AMF resulted in an increase in agronomic responses compared to untreated plants (Bl-–AMF) such as root biomass (+15%), stem diameter (+12%), plant height (+5%) and head diameter (+15%). Seed protein was higher in+AMF than–AMF (on average 20.7 vs 17.2 g m–2, respectively) and in Bh and Bm compared with Bl (on average 19.4 vs 18.2 g m–2, respectively). The oil content of seeds was affected by biochar application and AMF inoculation, especially under 50MAW and 30MAW irrigation levels; conversely, no differences were observed under the 10MAW irrigation level. Sunflower yield characteristics were positively correlated to the net photosynthesis rate and negatively affected by hydrogen peroxide and malondialde-hyde content. The results showed that the adoption of biochar and AMF may represent as a successful strategy to balance crop productivity in a semi-arid environment. Although further research is required for a better understanding of the irrigation and fertilization schedule, these preliminary results could be extended to other crops which have similar requirements to sunflower.