Purple Nonsulfur Bacteria Rhodopseudomonas palustris Improve Soil Phosphorus Availability and Yield of Lemon Balm (Melissa officinalis L.) in Alluvial Soils via Plant and Ratoon Seasons

Poorly nutritious soils limit the growth of crops. Moreover, lemon balm (Melissa officinalis L.) has never been applied with purple nonsulfur bacteria (PNSB). Therefore, this study was performed to (i) evaluate the phosphorus (P) providing capacity of PNSB and (ii) determine the effectiveness of the PNSB in ameliorating P uptake, growth, and yield of lemon balm in alluvial soils.

The experiment was designed in completely randomized blocks with nine treatments and three replications. The treatments from (1)-(4) were fertilizations of 100% P, 75% P, 50% P, and 25% according to the recommended fertilizer rate for lemon balm (RFRLB). The treatments (5-7) corresponded to the treatments (2-4), but they were combined with PNSB; the treatment (8) was applied with only PNSB, and the treatment (9) was applied without either chemical fertilization or PNSB.

The results showed that P fertilization combined with PNSB increased P_available by 14.1-24.2% as compared with the treatments with only chemical fertilization. Supplying both 75% P and PNSB improved lemon balm growth, such as the number of leaves per plant by 8.63%, the number of secondary branches by 7.69%, and essential oil content by 43.8% in season 1, and increased P uptake by 15.0-29.6% in both seasons.

A reduction of 25% P combined with PNSB maintained the yield of lemon balm like the 100% P fertilization in the two consecutive seasons because the PNSB solubilized unavailable P nutrient in the soil, leading to another P source rather than the chemical fertilizer.