Influence of co-applying biochar, compost and inorganic nitrogen on growth, nutrient uptake and nitrates and riboflavin content of turnips.

Abstract

In the pursuit of sustainable vegetable farming methods, the effect of co-application of biochar, compost, and a reduced amount of inorganic nitrogen on growth and the quality of turnips was studied in a greenhouse pot experiment. The experiment was carried out with six fertilizer treatments: unfertilized soil (US), compost + biochar (C+B), compost + 0.5 g N pot-1 (C+0.5N), biochar + 0.5 g N pot-1 (C+0.5N), compost + biochar + 0.5 g N pot-1 (C+B+0.5N), and pre-plant mineral fertilizer + 1 g N pot-1 (PF+N). Municipal organic compost collected selectively (150 g pot-1), biochar (20 g pot-1), and pre-plant mineral fertilization were mixed with the top 10 cm of soil. Inorganic nitrogen, was applied weekly in equal amounts. All treatments increased the N, P and K uptake and dry weight of roots and shoots, compared to unfertilized soil. Plant dry weight increase in the treatments C+0.5N, PF+N, and C+B+0.5N relative to the unfertilized soil was 767.7, 734.9, and 687.4%. Adding biochar to C+0.5N reduced Ca and Mg plant (root and shoots) uptake but did not affect the biomass accumulation. The root, shoot, and total plant dry weight of plants grown with C+0.5N and C+B+0.5N were not significantly different from those grown in inorganic fertilization (PF+N) only. Turnips grown with C+0.5N and C+B+0.5N accumulated similar biomass to those with inorganic fertilization (PF+N), while also reducing nitrate content. The co-application of compost with a reduced amount of nitrogen, can potentially eliminate or reduce the need for inorganic N, K, P, Ca and Mg while maintaining yield and quality. This study indicated that the addition of biochar to compost and inorganic nitrogen did not affect biomass accumulation, but reduced shoot riboflavin and thiamine contents of turnips.