Soil nitrogen dynamics drive regional variation in nitrogen use efficiency in rice: A multi‐scale study

Abstract

Northeast and East China account for ~36% of the Chinese rice cultivation area, yet considerable spatial disparities in nitrogen use efficiency (NUE) exist between these regions. The underlying causes remain poorly understood. Herein, we conducted a case study in two sample sites from two regions, Wuchang and Changshu, using multi‐scale evidence chains spanning macro‐ and micro‐ processes to identify the determinants of spatial NUE variability. Field studies showed higher NUE (partial factor productivity, PFP, and agronomic efficiency, AE) but lower ammonia volatilisation in Wuchang paddy soil. By separating edaphic factors from climatic conditions, soil replacement pot studies between Wuchang and Changshu revealed that both apparent (AE and recovery efficiency, RE) and 15N‐traced NUE were higher, whereas 15N fertilizer losses were lower in Wuchang‐soil than Changshu‐soil irrespective of site, suggesting soil type contributed to differences in soil N retention capacity and NUE of the soils. Process‐scale results showed that greater rates of gross N mineralizsation (13‐fold higher), gross nitrification (93% higher), and denitrification (52% higher) in Changshu‐soil compared to Wuchang‐soil corresponded to functional gene relative abundance, signifying larger reactive N losses and reduced soil N retention capacity. Microbial community analysis suggested that the differential N transformations were caused by differences in ammonia‐oxidizing archaea (AOA) family nitrososphaeraceae and Nitrospira‐like nitrite‐oxidizing bacteria (NOB). This highlights the importance of specific efficiency‐enhanced strategies tailored to the edaphic characteristics of cropping regions, such as increasing soil N retention capacity using enhanced‐efficiency fertilizer in East China, while implementing conservation management strategies in Northeast China. Highlights Field‐scale studies revealed higher NUE and lower NH3 volatilisation in Wuchang site. Soil replacement pot studies showed higher NUE in Wuchang‐soil regardless of sites. Process‐scale results unravelled high N losses and low soil N retention in Changshu‐soil. Varying NUE partially correlated with Nitrososphaeraceae AOA and Nitrospira‐like NOB.

Agronomic performance and remote sensing assessment of organic and mineral fertilization in rice fields

“…Soil nitrate-N levels before applying any amendment vary annually due to their sensitivity to rainfall and environmental conditions ( Liang et al., 1991 ; Zhao et al., 2023 ). During the period from sowing to flooding, nitrate N undergoes denitrification and quickly releases as N 2 and N 2 O following flooding ( Ponnamperuma, 1972 ; Li et al., 2018 ).…”