Humic Acid Improves Greenhouse Tomato Quality and Bacterial Richness in Rhizosphere Soil

Humic acid (HA) has attracted increasing attention as a new type of organic fertilizer in horticultural production, such as greenhouse-planted cherry tomato. However, we need more information to evaluate the effects of HA on soil rhizosphere bacteria and tomato performance under greenhouse conditions. In this study, greenhouse-planted cherry tomato was observed with HA added at dosages of 1500, 3000, 4500, and 6000 kg·ha^-1, respectively. The other two organic fertilizers [farmyard manure (FM) and commercial organic fertilizer (COF)], were used as comparison with a dosage of 3000 kg·ha^-1. Illumina MiSeq sequencing was conducted for bacterial diversity analysis, and tomato quality analysis based on total soluble solids, titratable acid, and sugar-acid ratio was performed for different fertilizer treatments. The results revealed that HA application resulted in the best flavor, compared to CK without the organic fertilizer used and with the other two organic fertilizers. The Chaol estimator and Shannon index showed that fertilizer addition decreased microbial diversity but increased species richness. At a dosage of 3000 kg·ha^-1, the effects of different fertilizers were ranked as HA > FM > COF. Our findings offered suggestions to reasonably optimize cherry tomato organic fertilizer application.