Cowpea (Vigna unguiculata L. Walp.) as a green manure to improve the productivity of a menthol mint (Mentha arvensis L.) intercropping system

Afield experiment was conducted at Central Institute of Medicinal and aromatic Plants (CIMAP), Lucknow, India in a sandy loam soil (entisol) during 2004 and 2005. Cowpea (Vigna unguiculata L Walp.) was intercropped with transplanted menthol mint (Mentha arvensis L.) for green manuring (GM) and for fodder plus green manuring (F+GM) with four levels of urea N (0, 30, 60, 90 kg N ha(-1)). In GM,cowpea was incorporated in the soil 30 days after sowing (DAS), while in F+GM 50% (alternate) cow pea plants were used for fodder at 30 DAS and 50% were incorporated in soil at 35 DAS. No significant differences were found between GM and F+GM with respect to herb and oil yield of menthol mint and succeeding palmarosa crop and nitrogen economy. Fresh biomass yield of menthol mint increased by 23.4% and essential oil yield by 25.2% by cowpea green manure(mean of GM and F+GM)as compared to without GM across all N levels. The contribution of green manure, as a nitrogen source, was equivalent to 30 kg N ha-1 when no fertilizer nitrogen was applied in menthol mint. The residual effect of cowpea GM was studied in a succeeding crop of fast growing essential oil yielding palmarosa (Cymbopopogon martinii (Roxb.)Wats. var motia Burk.) over two harvests (July and December). Averaged across N levels green manure resulted in an increase of 18.5% in the fresh biomass and 17.7% in essential oil yield of palmarosa over no green manuring. (C) 2009 Elsevier B.V. All rights reserved.