Effects of long-term combined organic-inorganic fertilizer application on soil aggregates and organic carbon
To investigate the impact of long-term combined application of organic and inorganic fertilizers on soil aggregate stability and organic carbon content,a 14-year field experiment was conducted with four treatments:no fertilizer(CK),chemical fertilizer only(CF),chemical fertilizer plus farmyard manure(OF),and chemical fertilizer plus bio-organic fertilizer(BF).The study examined the effects of different fertilization practices on soil aggregate stability and organic carbon content.The results showed that:① Fertilization(CF&OF&BF)increased the proportion of>2,1-2,and<0.053 mm size fractions,and the combined organic-inorganic fertilization(OF&BF)further enhanced the proportion of larger aggregates(>0.25 mm),promoted the transformation of micro-aggregates into macro-aggregates.②Combined organic-inorganic fertilization(OF&BF)improved the structure of soil aggregates,stability indexes of water-stable macro-aggregates such as large aggregate content(>0.25 mm)and stability indicators such as mean weight diameter and geometric mean diameter,with the best performance observed in the bio-organic fertilizer(BF)treatment.③ Among all treatments,the contribution rate of organic carbon from macro-aggregates(>0.25 mm)exceeded 62.0%,with the combined organic-inorganic fertilization showing a contribution rate of over 65.9%.Macro-aggregates were the primary storage size class for organic carbon,with 0.5-1 and 0.053-0.25 mm being important size ranges affecting soil organic carbon.④ Long-term combined organic-inorganic fertilization(OF and BF)increased the total soil organic carbon content,with bio-organic fertilizer being more beneficial for enhancing soil organic carbon levels.⑤ Compared to no fertilizer(CK),the variability in the contribution rate of organic carbon from farmyard manure(OF)and bio-organic fertilizer(BF)decreased by 43.6%and 45.7%,respectively.The distribution of organic carbon in each particle size fraction of the soil was more coordinted,and the stability of aggregate was enhanced.The above results indicated that combined organic-inorganic fertilization was beneficial to the transformation of micro-aggregates into macro-aggregates,increased the proportion of soil macro-aggregates,and balanced the contribution of organic carbon nutrients among different aggregate size classes.The effect was more pronounced with the addition of bio-organic fertilizer,which could provide a basis for long-term fertilization management.
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