Effect of fertiliser type and mycorrhizal inoculation on growth and development of sunflower (Helianthus annuus L.)

Biological farming practices using bio-inoculants and renewable organic supplements are being increasingly adopted by primary producers although little is known about their benefits compared to conventional fertiliser practices. Two trials were conducted on sunflower (Helianthus annuus L., 'Dwarf Sunsation') to compare the influence and interaction of arbuscular mycorrhizal fungi (AMF) inoculation with organic and conventional synthetic fertilisers on plant growth and development. Commercially produced AMF was applied as a spore application with liquid organic fertiliser (Quadshot®) applied at 0 and 20 L ha-1 in Trial 1; and 0, 20 L ha-1 and 40 L ha-1 in Trial 2, or liquid synthetic (inorganic) fertiliser (SF) applied at 0 or 100% concentration (Hoagland's solution regular strength with low P). Results showed limited interaction between AMF and fertiliser type. Sunflower plants inoculated with AMF and synthetic fertiliser had greater plant height and stem diameter in Trial 1 and leaf chlorophyll content at various assessment times in both trials. The presence of mycorrhizal hyphae and arbuscules increased in sunflower plants grown with AMF inoculation and organic fertiliser. There was a strong treatment influence of AMF inoculation on plant height in Trial 2, and number of nodes, flower head diameter, AMF colonisation and AMF structures in both trials. In addition, SF increased the leaf chlorophyll content, number of nodes and flower head diameter in both trials, and flower number in Trial 2. The organic fertiliser had negligible influence on sunflower productivity but improved leaf nutrient status. Standard concentration of SF improved sunflower productivity, and slightly improved leaf nutrient status compared to organic fertiliser. This study has demonstrated that while there were beneficial effects of AMF on plant growth, the use of organic fertiliser at the rates applied in this study did not benefit growth in the short term.