Abstract
Soil organic carbon (SOC) and nitrogen (N) fractions greatly affect soil health and quality. This study explored the effects of wheat straw incorporation on Chinese rice paddy fields with four treatments: (1) a control (CK), (2) a mineral NPK fertilizer (NPK), (3) the moderate wheat straw (3 t ha−1) plus NPK (MSNPK), and (4) the high wheat straw (6 t ha−1) plus NPK (HSNPK). In total, 0–5, 5–10, 10–20, and 20–30 cm soil depths were sampled from paddy soil in China. Compared with the CK, the HSNPK treatment (p < 0.05) increased the C fraction content (from 13.91 to 53.78%), mainly including SOC, microbial biomass C (MBC), water-soluble organic C (WSOC), and labile organic C (LOC) in the soil profile (0–30 cm), and it also (p < 0.05) increased the soil N fraction content (from 10.70 to 55.31%) such as the soil total N (TN) at 0–10 cm depth, microbial biomass N (MBN) at 0–20 cm depth, total water-soluble N (WSTN) at 0–5 and 20–30 cm depths, and total labile N (LTN) at 0–30 cm depth. The primary components of soil LOC and LTN are MBC and MBN. Various soil C and N fractions positively correlated with each other (p < 0.05). The HSNPK treatment promoted the soil MBC, WSOC, and LOC to SOC ratios, and also promoted MBN, WSTN, and LTN to soil TN ratios at a depth of 0–20 cm. To summarize, the application of HSNPK could maintain and improve rice paddy soil quality, which leads to increased rice grain yields.
Highlights
Soil organic carbon (SOC) plays a critical role in the global C cycle and dynamics [1]
Paddy fields serve as a primary source of greenhouse gases (e.g., CH4 and N2O) [2], and its labile C and nitrogen (N) stock changes might be linked to global greenhouse gas emissions
The SOC positively correlated with labile organic C (LOC), water-soluble organic C (WSOC), and microbial biomass C (MBC) (p < 0.01), and total N (TN) positively correlated with LTN, WSTN, and microbial biomass N (MBN) (p < 0.01). These findings suggested that after the crop straw residues were incorporated, the increase in the accumulation of SOC mostly came from the LOC, WSOC, and MBC
Summary
Soil organic carbon (SOC) plays a critical role in the global C cycle and dynamics [1]. Long-term addition of large amounts of C and N to farmland affects soil labile C and N [3]. Soil labile C and N are the most important parts of soil C and N stocks; they have far-reaching impacts on the soil C and N dynamics [4]. Soil organic matter alternations display slow degradation and are difficult to evaluate for short-term studies because of high background levels [5]. The content of labile organic matter is low because it is influenced by many factors (e.g., plants, microorganisms, and soil conditions), it has important meaning in soil quality changes and C/N cycling [3]. Because of the great difference in the physicochemical component and turnover times of various SOC fractions, there are great differences in the stability of soil C [6,7,8]
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