Lemon balm and kidney bean intercropping: the potential for incorporating AMF for sustainable agricultural production

This study investigated the effects of different cropping patterns and arbuscular mycorrhizal fungi (AMF) inoculation on the productivity of kidney bean and the essence quantity and quality of lemon balm. The cropping patterns included kidney bean monoculture (KBm), lemon balm monoculture (LBm), and additive intercropping ratios of 100% lemon balm + 15% kidney bean (LB/15 KB), 100% lemon balm + 30% kidney bean (LB/30 KB), 100% lemon balm + 45% kidney bean (LB/45 KB), 100% lemon balm + 60% kidney bean (LB/60 KB), with or without AMF inoculation. Monoculture produced the highest dry matter yield of lemon balm [139.1 g m^–2 (first harvest) and 121.0 g m^–2 (second harvest)] and seed yield of kidney bean (1315 kg ha^–1). AMF inoculation increased the dry matter yields of lemon balm by 9.6% and 10.9% (first and second harvests, respectively) and seed yield of kidney bean by 41.8%. The LB/45 KB intercropping ratio produced the highest essence content of lemon balm [0.17% (first harvest) and 0.16% (second harvest)], which did not significantly differ from those in LB/30 KB. Interestingly, AMF inoculation enhanced essence productivity by 33.3% in the first harvest and 21.4% in the second harvest. For both harvests, the GC–MS analyses identified 19 constituents in the lemon balm essence, with the major constituents being citronella, geranial, neral, trans-caryophyllene, and caryophyllene oxide. The LB/45 KB with AMF treatment produced the highest citronella content in both harvests. Concentrations of N, P, and K in most of intercropping patterns increased over the monocultures. We conclude that intercropping with AMF inoculation could be an agroecological strategy for improving the essence content, yield, and quality of lemon balm.