DOI: 10.5061/dryad.gqnk98sqg
title: Contribution of wheat and maize to soil organic carbon in a wheat-maize cropping system: a field and laboratory study

description: Retention of crop biomass is widely recommended to improve soil organic
 carbon (SOC). However, the magnitude of contribution of aboveground
 residues and belowground roots from C3 and C4 crops to SOC is unclear.
 Data from a 10-year field experiment and a 60-day laboratory incubation
 were synthesized to identify the respective contribution of C3 (e.g.,
 wheat) and C4 (e.g., maize) residues and roots to SOC, as well as its
 underlying mechanisms under no-till (NT) using 13C labelling trace in
 wheat-maize rotations. The field experiment showed that residue retention
 significantly increased SOC accumulation, and SOC derived from wheat was
 126.0% higher than that from maize. Conversion to NT promoted SOC derived
 from wheat and thus accumulated 17.6% higher SOC stock compared with plow
 tillage (PT) under residue returning at 0-20 cm soil depth
 (P&lt;0.05). The data from laboratory incubation revealed the
 mechanisms that lower priming effects at 0-10 cm depth decreased total
 mineralization by 91.8% after inputs of wheat residues and roots compared
 with that of maize residues and roots, especially under NT compared with
 PT. Priming effects were negatively correlated with enzyme activities
 associated with the C recycle, SOC, and total nitrogen (TN) contents
 (P&lt;0.01). NT increased enzyme activities, SOC, and TN contents and
 thus reduced priming effects and improved residual C. Synthesis and
 applications. These results suggested that wheat may contribute more to
 SOC accumulation than maize, and carbon increment efficiency in farmland
 could be enhanced by considering the crucial roles of C3 crops in SOC
 accumulation. NT practice sustains the benefits of C3 crops to SOC
 sequestration in the upper soil depths.
description: <strong>2.1. Field
 experiment</strong> In 2008, a field experiment was conducted at the
 Wuqiao Experimental Station of China Agricultural University, located in
 Hebei Province (Longitude of 37°36´N, Latitude of 116°21´E). Two tillage
 (NT and PT) and two residue managements [residue returning (RR) and
 residue removal (R0)] were combined into four treatments: no-till with
 residue retention (NTR), no-till with residue removal (NT0), plow tillage
 with residue incorporation (PTR), and plow tillage with residue removal
 (PT0) using a randomized block design. Each treatment was replicated three
 times with a plot area of 225 m<sup>2</sup> (15×15 m). Details
 of farm operations for experiment are presented in Table S1. Basic soil
 properties prior to experiment are presented in Table S2. Irrigation and
 fertilizer use were based on the local farmers' practice (Kan et al.,
 2020c). Wheat and maize were grown following an annual rotation
 cycle. <strong>2.2. Laboratory
 incubation</strong> Soil sampled from the field experiment during
 the wheat (June 2018) and maize season (October 2018) were incubated for
 60 days in a growth chamber. Soil incubation was done at a temperature of
 25 °C and a soil moisture content of 70% of water holding capacity (WHC).
 Soil moisture was measured over time through gravimetric methods, and
 distilled water was added to maintain at 70% WHC level. Labelled
 aboveground residues (δ<sup>13</sup>C=873.42‰ and 112.40‰ for
 wheat and maize) of wheat and maize were uniformly mixed at 3 g
 kg<sup>−1</sup> (sampled from wheat season) and 4 g
 kg<sup>−1</sup> dry soil (sampled from maize season),
 corresponding to 8.4 and 11.2 Mg ha<sup>−1</sup>, respectively
 at 0–20 cm depth (bulk density: 1.4 g cm<sup>−3</sup>).
 Similarly, labelled belowground roots (δ13C=537.38‰ and 106.79‰ for wheat
 and maize) were mixed with soils following the same procedure as with the
 aboveground residues. Methods of residue and root labelling are presented
 in the Supporting Information. Soils without residues (or roots) addition
 were used as a control. Basic properties of wheat and maize residues are
 shown in Table 1. A CO<sub>2</sub> trap (NaOH) was used to
 absorb the CO<sub>2</sub>, and the released
 CO<sub>2</sub> was measured on 5, 10, 20, 40, and 60 days
 after incubation. Carbonates were extracted by
 BaCl<sub>2</sub>, where
 Na<sub>2</sub>CO<sub>3</sub> was transformed to
 BaCO3 for δ<sup>13</sup>C analyses. The
 BaCO<sub>3</sub> was used to measure 13C abundance by
 ANCA-IRMS. The residual NaOH was titrated by HCl using
 phenolphthalein.