Effect of Mulching and Biochar Addition on the Distribution and Emission Characteristics of N2o from Furrow-Ridge Tillage Soils

Mulching and biochar are increasingly used individually in agriculture, but little is known about their combined effects on N2O distribution and dispersion in ridge and furrow profiles. We conducted a 2-year field experiment in northern China to determine soil N2O concentrations using the in situ gas well technique and calculate N2O emissions from ridge and furrow profiles by the concentration gradient method. The results showed that mulch and biochar increased soil temperature and moisture content and altered the available nitrogen status, leading to a decrease in the relative abundance of nitrification genes in the furrow domain and an increase in the relative abundance of denitrification genes, with denitrification remaining the main source of N2O production. N2O concentrations in the soil profile increased significantly after fertilizer application, and N2O concentrations in the ridge area of the mulch treatment were much higher than in the furrow area, where vertical and horizontal diffusion occurred. The addition of biochar was effective in reducing N2O concentrations and had no effect on the distribution and diffusion pattern of N2O. Soil temperature and moisture, but not soil available nitrogen, explained the variation in soil N2O emissions during the non-fertilizer 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 a 1.9%, 26.3% and 27.4% decreases in N2O emissions per unit of yield, respectively. There was a significant interaction between mulching and biochar on N2O emissions per unit of yield. Biochar costs aside, RFRB is very promising for increasing alfalfa yields and reducing N2O emissions per unit of yield