Towards sustainable production of peppermint (Mentha piperita L.) through integrated use of vermicompost and cowpea green manuring with synthetic nitrogen fertilization

A field experiment with peppermint (Mentha piperita L.) was conducted in a sandy loam (Typic ustifluvent) soil during 2007 and 2008 at Lucknow, India. Ten treatments consisting of control (no synthetic or organic nitrogen fertilization), synthetic nitrogen fertilization (SN) 75, 150 and 225 kg ha(-1) alone, vermicompost (VC) 3 t + 37.5 kg SN ha(-1), VC 6 t + 75 kg SN ha(-1) and VC 9 t + 112.5 kg SN ha(-1) and intercropping of one, two and three rows of cowpea for green manuring in combination with 50, 100 and 150 kg SN ha(-1), respectively, were evaluated in a randomized block design. Integrated use of VC 9 t with 112.5 kg SN ha(-1) produced maximum essential oil (94.3 kg ha(-1)), increased the herb and essential oil yields by 104 and 89%, respectively, over control and reduced SN use by 50%, without affecting the quality of essential oil. Application of VC and intercropping of cowpea for green manuring significantly improved the organic carbon, available N, P and K content in soil over SN alone. To get sustainable production of peppermint, application of VC 9 t ha(-1) along with 112.5 kg N ha(-1) through synthetic fertilizer is recommended for light textured sandy loam soils.