Utilization of inoculum of AM fungi produced on-farm increases the yield of Solanum lycopersicum: A summary of 7 years of field trials on a conventional vegetable farm with high soil phosphorus

•Three to seven cultivars of tomato were grown yearly and inoculated with AM fungi.•Mycorrhizal growth dependence after the greenhouse growth phase was 12.5%.•Overall mean mycorrhizal yield response was significant at 6.02%.

Adding arbuscular mycorrhizal [AM] fungus inoculum to potting media enables vegetable farmers to better take advantage of the AM symbiosis. On-farm production of AM fungus inoculum is a viable alternative to commercially-available inocula. We conducted a seven year experiment at a conventional vegetable farm in southeastern Pennsylvania with high soil available P typical of the Mid-Atlantic region of the USA (210 mg kg−1 soil). Seedlings of three to seven cultivars of Solanum lycopersicum L. were inoculated in the greenhouse phase of production with a mixed species inoculum of AM fungi produced on-farm. Performance of the inoculation treatment was evaluated based on growth response in the greenhouse and fruit production in the field compared to uninoculated controls. Colonization levels were typically only 1-10% of root length at the time of outplanting. The mean mycorrhizal growth dependency based upon shoot growth at the time of outplanting was significant at 12.5 ± 3.55% (α= 0.05). In addition, the mean mycorrhizal yield response over the seven year experiment was significant at 6.02 ± 1.92% (α= 0.05). Routine use of AM fungus inoculum produced on-farm provided a modest but significant increase in yield of tomato fruit with minimal change in farm management even in a high P soil.