Nutrient uptake, yield and taste of oilseed rape (Brassica napus L.) and soil chemical properties following amendment with uncomposted and composted tobacco waste and cattle manure

The inadequacy of the nutrient supply of most tropical and sub-tropical soils may be curbed through organic material recycling, thus reducing the need for mineral fertiliser use. To promote tobacco waste recycling in a smallholder food-cash crop production system, nutrient uptake, dry biomass yield and taste of oilseed rape (Brassica napus L.) and soil chemical properties were determined on a sandy loam soil under field conditions. The experiment was a randomised complete block design with three blocks and eight treatments, namely, control (no amendment), mineral fertiliser (121, 30.8, 24.6 kg/ha N, P and K, respectively), uncomposted tobacco leaf scrap (TSC) and compost of TSC and cattle manure (TSC-CM) at 5, 20 and 40 t/ha. N, P and K uptake and dry biomass yield of oilseed rape were higher (p<0.05) than control with 40 t/ha TSC-CM and mineral fertiliser application at 3 weeks after transplanting (WAT), while significant improvements with TSC were observed from 5 WAT. Mineral N, extractable P and exchangeable K were higher than control with TSC-CM at 20 t/ha and 40 t/ha at 3 WAT, and higher with TSC at 9 WAT. Soil organic carbon was more improved with TSC application than TSC-CM at 9 WAT. Organoleptic testing revealed an intensely bitter taste in oilseed rape with mineral fertiliser, 20 t/ha and 40 t/ha TSC at 3 WAT, although it diminished with time. A trade-off of nutrient uptake, yield, taste of oilseed rape and soil properties improvement is attainable with application of TSC-CM at 40 t/ha, while if composting is not feasible, TSC application at 20 t/ha is a viable alternative. Thus, judicious utilisation of tobacco waste offers a viable solution to the problem of low soil fertility on sandy soils and can reduce the need for mineral fertiliser use, while promising sustainable soil management. Significance: The study underlines the importance of recycling of organic materials as a viable, environmentally safe and low-cost soil fertility management practice. The study presents pragmatic practices that may be adopted so as to optimise the benefits of use of tobacco waste on food-cash crop smallholder farms, given the increasing popularity of such farming systems in Africa