Screening of genotypes of menthol mint Mentha arvensis for high yields of herbage and essential oil under late cropping conditions of the sub-tropical Indo-Gangetic plains

The essential oil yields and expression of related characters were compared for seven cultivar genotypes of menthol mint Mentha arvensis using two met hods of planting in the winter rabi - summer season (October to July) in a subtropical agroclimatic environment. The crops of all the cultivars were p lanted in the field by (1) sowing of suckers on 2 January and (2) transplan ting germinated pieces of sucker at different times between 17 March to 14 April. Staggering of transplanting time up to 7 April did not affect oil yi elds and the related plant growth properties of mint crops. The oil yields of the crops planted on 14 April were lower by about 30%. In the early suck er planted crops, the oil yields were about 30% higher than those obtained from the transplanted crops of 17 March to 7 April and about double that ob tained from crops transplanted on 14 April. The oil yields from the drops o f the superior genotype Kosi were equal to or higher than the corresponding means of all genotypes under both planting methods. The oil yield from the crops of Kosi genotype obtained by sucker sowing method was estimated as 3 33 kg hd(-1). The corresponding average yield from the crops of this genoty pe obtained by transplanting of germinated suckers between 17 March and 7 A pril was about 293 kg hd(-1) and that from the crop transplanted on 14 Apri l was 218 kg hd(-1). With the Kosi genotype, the latter two types of transp lanted mint crops gave oil yields lower only by about 12% and 33% compared with the long-duration sucker-sown crop. It is concluded that a crop of mus tard (brassica), Bengalgram (chickpea) or wheat sown between October and No vember and harvested between early March to middle of April could be taken before cropping of the Kosi genotype of M. arvensis by plantlet transplanti ng. These results demonstrate the potential of the following rotation of cr ops in the sub-tropical environments: from June/July/August to October/Nove mber (kharif cropping season), rice, maize, sorghum or pigeonpea; from Nove mber/December to February/March, mustard and Bengalgram or from November/De cember to April (rabi cropping season), wheat; from March/April to June/Jul y (zaid cropping season), transplanted menthol mint.