Characteristics of organic material inputs affect soil microbial <scp> NO <sub>3</sub> </scp> <sup>−</sup> immobilization rates calculated using different methods
Zhao‐Xiong Chen, Huimin Zhang, Xiaoshun Tu, Xin Sun, Jing Wang, Yi Cheng, Jinbo Zhang, Zu‐Cong Cai, Scott X. Chang
Abstract
Abstract Microbial immobilization of nitrate (NO 3 − ) is considered to be an important process in reducing NO 3 − accumulation and regulating nitrogen (N) retention capacity in soils. Accurately quantifying the rate of microbial NO 3 − immobilization is, therefore, necessary to predict its role in lowering NO 3 − accumulation in soils. We compared microbial NO 3 − immobilization rates using a 15 NO 3 − labelling technique in three different ways: (a) 15 N pool dilution, (b) organic 15 N recovery and (c) microbial biomass 15 N recovery, in a nitrate‐rich upland soil with and without amendment with organic materials with differing carbon‐to‐nitrogen ratios (C/N). The three methods generated similar NO 3 − immobilization rates, except when the soil was amended with easily decomposable organic materials (glucose and sucrose). We also developed a microbial NO 3 − immobilization‐specific quality index that incorporates the C/N ratio, lignin, cellulose and hemicellulose contents and pH for slowly decomposing organic materials (plant residues). This study provides direct empirical evidence that the results of different methods for calculating soil microbial NO 3 − immobilization rates are affected by the characteristics of organic materials added to the soil. Highlights Three methods for estimating microbial NO 3 − immobilization were compared The methods generated similar NO 3 − immobilization rates when amended with plant residues Higher NO 3 − immobilization when measured with 15 N dilution with readily available C input A microbial NO 3 − immobilization‐specific index for plant residues was developed