Journal
BIOLOGY AND FERTILITY OF SOILS
Volume 54, Issue 4, Pages 495-507Publisher
SPRINGER
DOI: 10.1007/s00374-018-1276-7
Keywords
N-15; N transformations; Nitrogen retention; Saturated soils
Categories
Funding
- National Natural Science Foundation of China [41771330, 41401339, 41330744, 31270556]
- Natural Science Foundation of Fujian Province [2014J01145]
- Foundation of Fujian Academic of Agricultural Sciences [AB2017-2, YC2015-6]
- Priority Academic Program Development of Jiangsu Higher Education Institutions
- UK Biotechnology and Biological Sciences Research Council
- BBSRC [BB/N013468/1] Funding Source: UKRI
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The connection between moisture and nitrogen (N) transformation in soils is key to understanding N losses, particularly nitrate (NO3-) losses, and also provides a theoretical framework for appropriate water management in agricultural systems. Thus, we designed this study to provide a process-based background for management decision. We collected soil samples from the long-term field experiment in subtropical China, which was designed to examine tobacco and rice rotations under a subtropical monsoon climate. The field experiment was established in 2008 with four treatments: (1) no fertilization as control; (2) N, phosphorus (P), and potassium (K) fertilizers applied at recommended rates; (3) N fertilizers applied at rates 50% higher than the recommended amounts and P and K fertilizers applied at recommended rates; and (4) N, P, and K fertilizers applied at recommended rates with straw incorporated (NPKS). Soil samples were collected during the unsaturated tobacco-cropping season and saturated rice-cropping season and were incubated at 60% water holding capacity and under saturated conditions, respectively. Two N-15 tracing treatments ((NH4NO3)-N-15 and NH4 (NO3)-N-15) and a numerical modeling method were used to quantify N transformations and gross N dynamics. Autotrophic nitrification was stimulated by N fertilizer both under unsaturated and saturated conditions. The rate of NO3- consumption (via immobilization and denitrification) increased under the NPKS treatment under saturated conditions. Secondly, the rates of processes associated with ammonium (NH4+) cycling, including mineralization of organic N, NH4+ immobilization, and dissimilatory NO3- reduction to NH4+, were all increased under saturated conditions relative to unsaturated conditions, except for autotrophic nitrification. Consequently, NO3--N and NH4+-N concentrations were significantly lower under saturated conditions relative to unsaturated conditions, which resulted in reduced risks of N losses via runoff or leaching. Our results suggest that under saturated conditions, there is a soil N conservation mechanism which alleviates the potential risk of N losses by runoff or leaching.
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