Abstract
To better understand the characteristics of soil organic matter (SOM) in the North China Plain, we evaluate the large scale variations of soil organic carbon (SOC), total nitrogen (TN), carbon to nitrogen (C:N) ratio and stable carbon isotopic compositions (δ13C) in SOC over 0–100 cm. To assess the influence of the Yellow River, 31 sites are selected from the wheat-maize double cropping system, and grouped into two: 10 sites near and 21 sites far from the river. Our data show that mean soil C:N ratio is low (7.6–9.9) across the region, and not affected by the Yellow River. However, SOC and TN are significantly (P < 0.05) lower in subsoil near the Yellow River (2.0 and 0.2–0.3 g kg−1 for SOC and TN) than far away (3.1 and 0.4 g kg−1); δ13C is significantly more negative below 60 cm near the river (−23.3 to −22.6‰) than far away (−21.8 to −21.4‰). We estimate that the contributions of wheat and maize to SOC are 61.3–68.1% and 31.9–38.8%, respectively. Our analyses indicate that the overall low levels of SOC in the North China Plain may be associated with the low soil C:N ratio and less clay content. The hydrological processes may also partly be responsible, particularly for those near the Yellow River.
Highlights
Land is an essential nature resource for sustainable agriculture
The natural 13C abundance (δ13C) in soil organic carbon (SOC) is another characteristic of organic matter, which is largely related to sources of organic carbon, and affected by decomposition[20,21]
River than far away (P < 0.05), but average electric conductivity (EC), total dissolved solids (TDS), water-soluble Ca2+ and Mg2+ contents are significantly higher in the topsoil near the river than far away (P < 0.05, Table 1)
Summary
Land is an essential nature resource for sustainable agriculture. Maintaining good soil quality is important for high grain production. The North China Plain has a long history of intensive cropping, and is an important grain production base in China. This region counts 57% of the nation’s wheat-grow land and provides 66% of the nation’s wheat productivity[6]. Given the fact of relatively larger land with lower soil fertility ( lower rates of production) in the northwest China, maize yield in the North China Plain would be much above average. Based on these analyses, one may expect that soil fertility SOM or SOC in the North China Plain should be above average of China. Limited studies have employed this approach to quantify the contributions of wheat and maize to SOC in the northern China[26,27]
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