Influence of Natural Essential Oils and Synthetic Nitrification Inhibitors on Crop Yield and Nitrogen Use Efficiency in Mint (Mentha arvensis L.)-Mustard (Brassica juncea L.) Cropping Sequence

Field investigations were carried out at the Central Institute of Medicinal and Aromatic Plants (CIMAP), Lucknow (UP.) during 1997–98 to study the relative efficiency of different natural urease/nitrification inhibitors in Japanese mint (Mentha arvensis cv. Hy 77) and their residual influence on the succeeding crop of mustard (Brassica juncea cv. Varona). Results indicated that urea coated with different natural essential oils was significantly superior to uncoated urea at both the rates of fertilizer nitrogen treatments. Mint herb, essential oil yield and nitrogen uptake were significantly higher with the coated urea over the uncoated urea. Treatments were more effective at 100 kg N ha⁻¹ rate of fertilizer application; the response to sources of N was in the order: Mentha spicata oil coated urea > Artemisia annua oil coated urea > dicyandiamide (DCD) coated urea > uncoated urea. However, trend was different at 200 kg N ha⁻¹; it was in the order A. annua oil coated urea > M. spicata oil coated urea > DCD coated urea > uncoated urea. The results indicated that these coated fertilizers applied to mint were able to yield higher as compared to ordinary urea under mint-mustard rotation. Pre-mustard soil analysis revealed that these natural coating materials enhanced the organic C and available nitrogen in soil. Seed and stover yield, nitrogen uptake and apparent nitrogen recovery in mustard were higher with the residual effect of coated urea than uncoated urea.