Effect of mulching and biochar addition on the distribution and emission characteristics of N 2 O from furrow-ridge tillage soils.

Mulching and biochar are increasingly used individually in agriculture, but little is known about their combined effects on N ₂ O distribution and dispersion in ridge and furrow profiles. We conducted a 2-year field experiment in northern China to determine soil N ₂ O concentrations using the in situ gas well technique and calculate N ₂ O fluxes from ridge and furrow profiles by the concentration gradient method. The results showed that mulch and biochar increased soil temperature and moisture and altered the mineral nitrogen status, leading to a decrease in the relative abundance of nitrification genes in the furrow area and an increase in the relative abundance of denitrification genes, with denitrification remaining as the main source of N ₂ O production. N ₂ O concentrations in the soil profile increased significantly after fertiliser application, and N ₂ O concentrations in the ridge area of the mulch treatment were much higher than those in the furrow area, where vertical and horizontal diffusion occurred. Biochar addition was effective in reducing N ₂ O concentrations but had no effect on the N ₂ O distribution and diffusion pattern. Soil temperature and moisture, but not soil mineral nitrogen, explained the variation in soil N ₂ O fluxes during the non-fertiliser application period. Compared to furrow-ridge planting (RF), furrow-ridge mulch planting (RFFM), furrow-ridge planting with biochar (RBRF) and furrow-ridge mulch planting with biochar (RFRB) resulted in 9.2%, 11.8% and 20.8% increases in yield per unit area and 1.9%, 26.3% and 27.4% decreases in N ₂ O fluxes per unit of yield, respectively. The interaction between mulching and biochar significantly affected the N ₂ O fluxes per unit of yield. Biochar costs aside, RFRB is very promising for increasing alfalfa yields and reducing N ₂ O fluxes per unit of yield.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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