CH4 fluxes and diffusion within soil profiles subjected to different fertilizer regimes on China's Loess Plateau

To better understand the effects of fertilizer on soil methane (CH4) diffusion and consumption in semi-arid region, we investigated the subsurface CH4 concentrations at seven depths in the mineral soil and analysed the CH4 fluxes between soil horizons at the Changwu Agro-Ecological Station on China's Loess Plateau. The results showed that dryland soil was a weak net CH4 sink. The CH4 concentration and diffusion decreased with increasing depth to a depth of 50 cm, and then remained low from 50 to 100 cm. Much of the soil CH4 diffusion and transformation occurred in the top 20 cm, but maximum CH4 production occurred at a depth of 7 cm, and maximum CH4 consumption occurred at a depth of 15 cm. Soil moisture could significantly inhibit gas diffusion and accelerate the biochemical transformation of CH4. In high-yield production system, the application of nitrogen fertilizer promoted CH4 diffusion, especially in the surface soil, but did not affect the transformation of CH4; thus, organic matter promoted CH4 diffusion and stimulated CH4 transformation, especially for CH4 consumption at a depth of 15 cm. Overall, the integrated application of manure and nitrogen fertilizer can not only have optimum yield, but also successfully play a very low risk of CH4 emission.