Abstract
Cropland soil organic carbon (SOC) is undergoing substantial alterations due to both environmental and anthropogenic changes. Although numerous case studies have been conducted, there remains a lack of quantification of the consequences of such environmental and anthropogenic changes on the SOC sequestration across global agricultural systems. Here, we conducted a global meta-analysis of SOC changes under different fertilizer managements, namely unbalanced application of chemical fertilizers (UCF), balanced application of chemical fertilizers (CF), chemical fertilizers with straw application (CFS), and chemical fertilizers with manure application (CFM). We show that topsoil organic carbon (C) increased by 0.9 (0.7–1.0, 95% confidence interval (CI)) g kg−1 (10.0%, relative change, hereafter the same), 1.7 (1.2–2.3) g kg−1 (15.4%), 2.0 (1.9–2.2) g kg−1 (19.5%) and 3.5 (3.2–3.8) g kg−1 (36.2%) under UCF, CF, CFS and CFM, respectively. The C sequestration durations were estimated as 28–73 years under CFS and 26–117 years under CFM but with high variability across climatic regions. At least 2.0 Mg ha−1 yr−1 C input is needed to maintain the SOC in ~85% cases. We highlight a great C sequestration potential of applying CF, and adopting CFS and CFM is highly important for either improving or maintaining current SOC stocks across all agro–ecosystems.
Highlights
Compared with the mean ΔSOC using the last year of observations (3.5 g kg−1, Fig. 2a), the result obtained using multiple-year observations was 4.2 g kg−1 under chemical fertilizers with manure application (CFM) (Fig. S3a), while Maillard and Angers[15] estimated the ΔSOC was 1.0–4.1 g kg−1 under CFM
The cool temperate zone accumulated more C (Fig. 3a) due largely to the associated longer fertilization duration – 26 yr, compared with 12 and 16 yr for tropical and warm temperate regions, respectively. This was supported by evidences from Maillard and Angers[15] and Tian et al.[31], both confirming that cool temperate accumulated more C than tropical
The relative changes under the four treatments were generally lowest in cool temperate and highest in tropical regions (Fig. 3b), which might be caused by different initial soil organic carbon (SOC) conditions (i.e., 15.8, 11.6 and 7.8 g kg−1 in cool temperate, warm temperate and tropical regions, respectively)
Summary
Manure application and stubble retention are among the most predominant management practices driving SOC changes because they directly add C into soil[14,15]. With the expansion of conservation tillage[21] and organic farming[22], the residue incorporation and manure application rates are certain to increase in the areas where such RMPs are adopted, promoting soil C sequestration[23,24]. Complete crop residue removal for fodder and fuel is a norm in South Asia and Africa[1], making soils in these areas lack of organic matter input and liable to be C sources. Our objectives were to 1) quantify the SOC changes under different fertilizer managements and 2) identify and quantify the factors (i.e., environmental and management conditions) with the most influence on SOC changes
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