Composted tobacco waste increases the yield and organoleptic quality of leaf mustard

Tobacco (Nicotiana tabacum) waste is produced in many countries and is phytotoxic due to the alkaloid content; in Vietnam the waste is usually burned causing air pollution. We composted tobacco waste with chicken manure in different proportions—1 t of waste ± accelerant (C₁ and C₂); 0.8 t of waste + 0.2 t of chicken manure ± accelerant (C₃ and C₄); and 0.7 t of waste + 0.3 t of chicken manure ± accelerant (C₅ and C₆)—for 30 d in covered heaps. Three mixtures containing the accelerant (C₂, C₄, and C₆) reached temperatures of ∼55 °C, that 5s, hot enough to suppress disease and weeds. Composting decreased the alkaloid content from ∼6,000 to ∼200 mg kg⁻¹, and C₄ with a C/N ratio of 19:1, was used in a field trial. The compost treatments (0, 10, 15, and 20 t ha⁻¹) were combined fertilizer with phosphorus (40 kg ha⁻¹), nitrogen (60 kg ha⁻¹) and potassium (90 kg ha⁻¹) for leaf mustard (Brassica integrifolia). The yield increased from ∼17 to ∼29 t ha⁻¹ with the amount of compost applied, and the nitrate concentration decreased concomitantly from ∼67 to ∼42 mg NO₃–N kg⁻¹ fresh weight, presumably due to ongoing composting (nitrogen drawdown). Organoleptic evaluation showed a preference for the crops grown with the compost amendments. Whether remains to be seen whether one-off compost applications >20 t ha⁻¹ and repeated, large applications provide additional, long-term production benefits, or if the benefits may be outweighed by the accumulation of persistent, phytotoxic alkaloids.