Date Published: February 7, 2017
Publisher: Public Library of Science
Author(s): Yuling Zhang, Wenjing Xu, Pengpeng Duan, Yaohui Cong, Tingting An, Na Yu, Hongtao Zou, Xiuli Dang, Jing An, Qingfeng Fan, Yulong Zhang, Ben Bond-Lamberty.
Understanding the nitrogen (N) mineralization process and applying appropriate model simulation are key factors in evaluating N mineralization. However, there are few studies of the N mineralization characteristics of paddy soils in Mollisols area of Northeast China.
The soils were sampled from the counties of Qingan and Huachuan, which were located in Mollisols area of Northeast China. The sample soil was incubated under waterlogged at 30°C in a controlled temperature cabinet for 161 days (a 2: 1 water: soil ratio was maintained during incubation). Three models, i.e. the single first-order kinetics model, the double first-order kinetics model and the mixed first-order and zero-order kinetics model were used to simulate the cumulative mineralised N (NH4+-N and TSN) in the laboratory and waterlogged incubation.
During 161 days of waterlogged incubation, the average cumulative total soluble N (TSN), ammonium N (NH4+-N), and soluble organic N (SON) was 122.2 mg kg-1, 85.9 mg kg-1, and 36.3 mg kg-1, respectively. Cumulative NH4+-N was significantly (P < 0.05) positively correlated with organic carbon (OC), total N (TN), pH, and exchangeable calcium (Ca), and cumulative TSN was significantly (P < 0.05) positively correlated with OC, TN, and exchangeable Ca, but was not significantly (P > 0.05) correlated with C/N ratio, cation exchange capacity (CEC), extractable iron (Fe), clay, and sand. When the cumulative NH4+-N and TSN were simulated, the single first-order kinetics model provided the least accurate simulation. The parameter of the double first-order kinetics model also did not represent the actual data well, but the mixed first-order and zero-order kinetics model provided the most accurate simulation, as demonstrated by the estimated standard error, F statistic values, parameter accuracy, and fitting effect.
Overall, the results showed that SON was involved with N mineralization process, and the mixed first-order and zero-order kinetics model accurately simulates the N mineralization process of paddy soil in Mollisols area of Northeast China under waterlogged incubation.
Nitrogen (N) mineralization is not only a foundational step in soil organic N transformation, but it is also one of the most important processes in soil N cycling. More than 50% of N that is absorbed during rice growth is from the soil, regardless of whether or not N fertilizer has been applied [1, 2]. In fact, approximately 50%–80% of N is absorbed from the soil by high-yield rice . During the N mineralization process, soil organic N is mineralised into inorganic N primarily in the forms of ammonium N (NH4+-N) and nitrate N (NO3−-N), or is transformed into an intermediate transitional fraction as soluble organic N (SON), which is then mineralised into inorganic N. Therefore, SON could be an available N source for plants. Historically, most studies on paddy soil N mineralization have focussed on soluble inorganic N and little attention has been paid to SON in leachates [3–6]. Therefore, a more accurate simulation of the N mineralization process in paddy soil is important to guide strategies for the rational application of fertilizer in rice production.
The study was approved by the government of Qingan and Huachuan counties, which are located in Mollisols area of Northeast China. All experimental procedures were conducted in Shenyang Agricultural Univeristy.
This study resulted in two major conclusions that will be valuable in developing effective N fertilization strategies to increase productivity of paddy soil. Firstly, during the period of waterlogged incubation of paddy soil in Mollisols area of Northeast China, mineralization NH4+-N was significantly (P < 0.05) positively correlated with OC, TN, pH, and exchangeable Ca, and mineralization TSN was significantly (P < 0.05) positively correlated with OC, TN, and exchangeable Ca, but was not significantly (P > 0.05) correlated with C/N ratio, CEC, extractable Fe, clay, and sand. The ratio of cumulative SON to NH4+-N or TSN was 54.0% and 32.5%, respectively, and TSN showed a stronger linear correlation with OC or TN when considering SON. Therefore, SON should be considered during evaluations of N mineralization.