The effect on soil nitrogen mineralization resulting from biochar and straw regulation in seasonally frozen agricultural ecosystem

Abstract To thoroughly explore the effects of different regulation measures on soil nitrogen cycling in seasonally frozen areas, four treatments, natural control (BL), biochar addition (BA), straw addition (SA) and combined of biochar and straw (CBS), were established on the Songnen Plain of Northeast China. Variations in soil moisture, temperature and urease activity were analyzed. In addition, the mineralization rate was calculated based on the changes of soil inorganic nitrogen content. Furthermore, the response functions of the soil nitrogen mineralization rate were constructed, and the response mechanism for the effect of different regulation patterns on soil nitrogen was determined. It showed that during the freezing period, straw mulch effectively inhibited the loss of soil water and heat, and hindered the reduction in soil urease activity; the average soil urease activity under the SA treatment increased by 0.390, 0.272, and 0.157 mg⋅(g−1·d−1) relative to those under the BL, BA, and CBS treatments, respectively. During the thawing period, the combined of bio char and straw had better heat preservation and water conservation, which greatly enhanced the activity of soil urease. The regulation of biochar and straw significantly affected the soil nitrogen mineralization rate its relationship with influencing factors. During the freezing period, the inorganic nitrogen content was the highest under the SA treatment. During the thawing period, the combined of biochar and straw enhanced the accumulation of soil nitrogen, and the response of the nitrogen mineralization rate to soil water, heat, and urease activity was strongest. In addition, the regulation abilities of biochar and straw decreased with increasing soil depth. These research results have important significance for understanding nitrogen transformations and efficiently guiding agricultural cleaner production.