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Figure 1 Soil aggregate stability in terms of mean weight diameter (MWD) and geometric mean diameter (GMD) in a typical red soil under long-term fertilizations. Different letters in columns indicate significant differences (p < 0.05) between treatments. CK: un-fertilized control; NPK: mineral fertilization; NPKM: mineral + manure fertilization. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.) Irrespective of the studied treatments, macro-aggregates of >250 pm size showed the highest OC contents (3.65-8.63 g kg~1), while the lowest was for micro-aggregates of <53 pm (1.71-2.49 g kg!) (Table 1). OC contents for macro-aggregates of >250 jm were 3.65, 5.44 and 8.63 g Ckg / under control, NPK application and NPKM treatment, respectively. Similarly, for 250-53 ym meso-aggregates, OC contents were 2.27, 3.13 and 3.60 g kg! under control, NPK application and NPKM treatment, respectively. Likewise, for micro-aggregates of <53 um OC contents were 1.71, 2.29 and 2.49 gkg! under CK, NPK and NPKM treatments. In other words, the application of NPK and NPKM resulted in 49 and 136% increases of OC contents in macro-aggregates of >250 pm, 37.8 and 59% increase in 250-53 jm meso-aggregates, and 34 and 46% increase <53 pm micro-aggregates, as compared to control (CK). Moreover, consistent with the SOC stock in bulk soil, the appli- cation of NPK and NPKM resulted in increased SOC stock in all aggre- gates (Fig. 3b—d). An increase of 47 and 101% was observed in SOC stock in macro-aggregates of >250 ym size under application of NPK and NPKM respectively, compared to control. SOC content was increased by 30 and 103% in 250-53 pm size meso-aggregates, due to the application of NPK and NPKM, respectively, compared to CK. Regarding micro- aggregates (<53 ym), the application of NPK and NPKM caused 30 Long-term organic and mineral fertilization led to significant varia- tions in total OC and TN contents, which were in the order CK< NPK< NPKM. Compared to CK, inorganic NPK fertilization significantly (P < 0.05) (Table S3, Supplementary materials) increased SOC and TN in bulk soil (Table 1). However, the highest contents of OC and TN were observed under inorganic plus manure application (NPKM). The appli- cation of NPK and NPKM resulted in 45.45 and 97.86% increase in OC contents, as compared to CK. Similarly, consistent with the findings observed for OC, NPK, and NPKM fertilization increased TN contents up to 60 and 141.81%, as compared to CK. Total SOC had a strong positive relation with aggregate associated carbon contents (Fig. 2a and b, c). The stocks of SOC and TN were considerably higher under fertilization
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