Chemical fertilizers are commonly used for controlled environment agriculture because they provide essential plant nutrient efficiently. However, rising fertilizer costs, global phosphorous shortage, and the negative impacts of producing and using chemical fertilizer are concerns for sustainable crop production. As sustainable alternatives to chemical fertilizers, there is a growing interest in using organic fertilizers with beneficial plant growth promoting microorganisms. The objectives of this research were to investigate how the application of plant growth promoting bacteria and arbuscular mycorrhizal fungi influences plant growth of lettuce (Lactuca sativa) and tomato (Solanum lycopersicum) seedlings in soilless media under organic fertilization. In the first study, the effects of Azosprillium brasilense and Rhizophagus intraradices inoculation on lettuce and tomato seedling growth were quantified under two different organic fertilizer types compared to under chemical fertilizer. The results showed that A. brasilense and R. intraradices had little to no effect on any growth parameter measured in either species regardless of fertilizer type. In the second study, an investigation of the co-inoculation of A. brasilense and R. intraradices or increasing the application frequency of A. brasilense or/and R. intraradices increased plant growth promoting effects in lettuce ‘Cherokee’ and ‘Rex’ grown under organic fertilization. An application frequency of every 2-days of the R. intraradices without or with A. brasilense increased shoot fresh weight in both lettuce cultivars by 51-58%, compared to un-inoculated control. In contrast, lettuce seedling growth were similar without or with applying R. intraradices weekly or A. brasilense regardless of frequency. Together, the results suggest that applying R. intraradices with a proper application frequency can enhance plant growth of lettuce under organic fertilization.

As the global population continues to increase, so does the need for agriculture resulting in increased fertilizer use. Nanofertilizers and biochar have been proposed as alternatives to fertilizers currently in use to reduce negative environmental impacts. In this study, the effects of various nanofertilizers and biochar on the soil microbial community were investigated. Soils treated with graphene nanoplatelet (GNP), graphene oxide (GO), reduced graphene oxide (rGO), graphite nano-additive (GNA) and biochar (BC) at concentrations of 5 mg/kg and 1000 mg/kg were sampled before and after a 28-day incubation period. Quantitative PCR assays were carried out against the following target genes: 16S rRNA, nirK, nirS, nifH, amoA and nosZ. Overall, all treatments experienced a decrease in 16S rRNA abundance after the incubation period with an average decrease of 48% however, all treatments were higher in abundance than the control. The abundances of nitrogen (N) cycling functional genes were evaluated in terms of relative abundance as a percentage of 16S rRNA. There was an increase across all treatments in nirK relative abundance over time and when compared to the control. The most notable differences in abundance were in rGO (high) as well as BC. Both nirS and nosZ exhibited an increase over time but decreased compared to the control. A decrease in relative abundances of nifH in BC as well as GO (low) and rGO (high) was observed. Lastly, there was an increase in amoA relative abundance across all treatments after the incubation period. However, all treatments were significantly lower than the control. The increase of denitrifying genes (nirK, nirS and nosZ) and nitrifying genes (amoA) suggests the potential increase in denitrification which can result in increased N loss into the atmosphere and the potential decrease of nitrification resulting in reduced N loss into waterways, respectively. At the time of writing, this study is one of the first to investigate and provide observations on the effects of nanofertilizers on nifH, which is responsible for N-fixation. The results presented here suggest that rGO and BC impart similar effects on the microbial community, whereas GNP had the most significant impact overall.