Effects of Freezing–Thawing Processes on Net Nitrogen Mineralization in Salinized Farmland Soil

Nitrogen is an indispensable and limiting element for plant microbial growth. To investigate the combined effects of salinity freezing–thawing (FT) processes on soil inorganic nitrogen (SIN) transformation in seasonally freezing salinized farmland, laboratory incubation experiments were conducted under five salt content (SSC) treatments (0.08%, 0.25%, 0.35%, 0.50%, 0.70%), four FT temperature (C (5 °C), (−5 + 5 (−10 (−15 °C)), two water (SWC) (40% 80% maximum holding capacity (WHC)). Ammonium (NH4+-N) nitrate (NO3−-N) monitored at first, second, fifth, eighth days. The increased relative NH4+-N by 13%, 39%, 77% with decreasing from −5 °C to −15 compared C °C) treatments, respectively. decreased NO3--N contents 4% 6% Under increment was higher low-SSC lower high-SSC treatments. relationship between NO3–-N SSC gradually changed a decrease increase (−15+5 SWC low-freezing (SSC × < −2.5%· while unfrozen variations SIN/Rmin (nitrogen mineralization rate) mostly affected NO3–-N/Rnit (net nitrification NH4+-N/Ra ammonification Overall, results suggested that enhanced inhibited NO3−-N formation, weakened formation induced temperature, this function salinity.