On the North China Plain, low soil organic carbon (SOC) content and a consistently dropping underground water level are seriously threatening food production security. To date, the interactive effect of fertilization types and irrigation regimes on surface and subsurface SOC contents has rarely been quantified. Here, we conducted a field study of three irrigation regimes with two fertilization types between 2009 and 2018. The three irrigation regimes included presowing irrigation (W0); presowing and jointing irrigation (W1); and presowing, jointing and anthesis irrigation (W2). The two fertilization types were mineral fertilizer only (CF) and mineral fertilizer plus composted chicken manure (CFM). Soil samples were collected from a depth of 0−100 cm in 20-cm increments to measure SOC and its composition, including labile pool I (LPI) (polysaccharides), labile pool Ⅱ (LPⅡ) (cellulose), and recalcitrant pool (RCP). Four SOC-related enzymes were determined, i.e., α-glucosidase, β-glucosidase, peroxidase and polyphenol oxidase. Stable carbon isotopic (¹³C) analysis was determined to distinguish the contributions of wheat- and maize-derived SOC in a wheat-maize rotation. The results showed that the 0−20-cm SOC content was highest in the W0 + CFM treatment. In the 0−20-cm layer, SOC decreased from W2 to W1 or W0 under CF, which is attributed to a reduction in the labile pool and maize-derived C and higher polyphenol oxidase. Conversely, under CFM, the 0−20-cm SOC content increased following decreased irrigation from W2 to W1 and from W1 to W0, mainly due to the increased LPⅡ and RCP. Compared with CF at W0 and W1, the 0−20-cm SOC content increased by 30.5 % and 21.8 % under CFM, respectively. Relative to the 0−20-cm soil layer, the SOC stock was larger in the 20−100-cm layer, which of the treatments had a variation manner similar to the 0−20-cm soil layer. Our results suggest that reduced irrigation regimes have significantly reduced the SOC stock and altered its composition in the 0−100-cm soil layer under CF and that CFM can increase the SOC stock in this layer when reducing the irrigation regime.

在华北平原，土壤有机碳含量低和地下水位持续下降严重威胁着粮食生产安全。迄今为止，很少量化施肥类型和灌溉方式对地表和地下SOC含量的相互作用。在这里，我们对2009年至2018年间三种施肥方式的三种灌溉方式进行了实地研究。播前和节水灌溉（W1）；以及播种，拔节和花药灌溉（W2）。两种肥料类型为仅矿物肥料（CF）和矿物肥料加鸡粪堆肥（CFM）。从0-100 cm的深度以20 cm的增量采集土壤样品，以测量SOC及其组成，包括不稳定的Ⅰ类（LPI）（多糖），不稳定的Ⅱ类（LPⅡ）（纤维素）和顽calc性（RCP）。确定了四种与SOC相关的酶，即α-葡萄糖苷酶，β-葡萄糖苷酶，过氧化物酶和多酚氧化酶。稳定的碳同位素（¹³C）确定分析以区分小麦和玉米轮作中小麦和玉米来源的SOC的贡献。结果表明，W0 + CFM处理的0-20 cm SOC含量最高。在0-20cm层，SOC在CF下从W2下降到W1或W0，这归因于不稳定库和玉米衍生的C的减少以及多酚氧化酶的增加。相反，在CFM下，从W2到W1和W1到W0的灌溉减少，0-20 cm SOC含量增加，这主要是由于LPⅡ和RCP的增加。与W0和W1处的CF相比，CFM下0-20cm SOC含量分别增加了30.5％和21.8％。相对于0-20 cm土层，SOC储量在20-100 cm层中更大，这两种处理方式的变化方式都类似于0-20 cm土层。