Contents lists available at ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma Balancing nutrient stoichiometry facilitates the fate of wheat residue‑carbon in physically defined soil organic matter fractions Yunying Fang a, ⁎ ,1 , Bhupinder Pal Singh a,b,1 , Annette Cowie c , Weiqi Wang d , Meragal Henaka Arachchi a , Hailong Wang e,f , Ehsan Tavakkoli g,h a NSW Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Menangle, NSW 2568, Australia b School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia c NSW Department of Primary Industries, Trevenna Rd, Armidale, NSW 2351, Australia d Key Laboratory of Humid Subtropical Eco-geographical Process, Ministry of Education, Fujian Normal University, Fuzhou, Fujian 350007, China e School of Environment and Chemical Engineering, Foshan University, Foshan, Guangdong 528000, China f School of Environmental and Resource Sciences, Zhejiang A&F University, Hangzhou, Zhejiang 311300, China g NSW Department of Primary Industries, Wagga Wagga Agricultural Institute, Wagga Wagga, NSW 2650, Australia h Graham Centre for Agricultural Innovation, Charles Sturt University, Wagga Wagga, NSW 2650, Australia ARTICLE INFO Handling Editor: David Laird Keywords: 13 C isotope Soil organic matter Crop stubble residue Density fractionation Particle size fractionation Organo-mineral interaction ABSTRACT Preserving and enhancing soil organic carbon (SOC) stocks is one of the major objectives for sustainable agri- culture. The exogenous nutrient supply along with returning crop residues, i.e., integrated residue-nutrient management, may increase carbon (C) cycling and residue-derived microbial biomass, and therefore to affect SOC stocks. However, there is a lack of knowledge about how the integrated residue-nutrient management, that balances the resource nutrient stoichiometry, facilitates the fate (or partitioning) of residue-C in physically defined SOC fractions. Hence, through a laboratory study, we quantified the fate of wheat residue (δ 13 C-en- riched, 494‰) into sequentially separated physical SOC fractions, under the interaction of different residue rates (6.7 and 20.0 g kg -1 soil) and nutrient inputs (nil, low and high supplies of nitrogen, phosphorus, and sulfur) in two contrasting soils (Luvisol and Vertisol). The results showed that after 245 days, 42.7–54.2% of the newly- added residue- 13 C remained in organic matter (OM) fractions in the soils, with 22.1–40.8% in the light fraction [LF; defined as free particulate organic matter (f-POM)] and 13.9–19.5% in the heavy fraction [HF; defined as aggregate- & mineral-protected OM, which included silt-clay OM and occluded POM (o-POM)]. Following the sequential separation of HF, 8.3–15.3% of residue- 13 C was distributed to silt-clay OM and 4.2–6.1% to o-POM after 245 days. The high-residue rate (cf. low-residue) increased the amount of residue-C in SOC fractions. Narrowing the C-nutrient stoichiometric ratio in the residue treated soils via the exogenous nutrient input af- fected the proportional distribution of residue-C in SOC fractions at the high-residue rate only. With the high- residue rate in both soils, nutrient input (cf. no-nutrient) at both rates increased “new” residue-derived stable C formation in the HF by 17% or silt-clay associated OM by 27%, while decreased the distribution of residue- 13 C in the f-POM (LF) by 26% or o-POM by 18%. In the current study, soil type also affected the incorporation of residue-C in the organo-mineral fractions, i.e., 20% higher residue-C was incorporated in the silt-clay OM in the Vertisol than Luvisol. This study improved our knowledge on the distribution of residue-C in SOC fractions in response to integrated residue-nutrient management, which could be used to refine conceptual and mechanistic models for predicting changes in SOC storage. 1. Introduction Globally, there is a great interest in improving soil properties and functionality through agricultural management practices, including the combined input of crop residue and nutrients, known as “integrated residue–nutrient management” (Han et al., 2016; Tian et al., 2015). A study by Mitchell et al. (2018) has shown that increasing plant residue inputs in a soil increased residue-derived soil organic matter (SOM) formation and stabilization, such as gains in particulate organic matter (POM) and mineral-associated SOM fractions. Moreover, the exogenous https://doi.org/10.1016/j.geoderma.2019.113883 Received 18 April 2019; Received in revised form 20 July 2019; Accepted 22 July 2019 ⁎ Corresponding author. E-mail address: yunying.fang@dpi.nsw.gov.au (Y. Fang). 1 Both authors contributed equally to this work. Geoderma 354 (2019) 113883 0016-7061/ © 2019 Elsevier B.V. All rights reserved. T