Organic amendment effects on aggregate-associated organic C, microbial biomass C and glomalin in agricultural soils

To evaluate the effects of organic amendments on soil aggregate stability and aggregation-associated soil characteristics, a study was initiated in agricultural soils after 4 years of organic amendments. Soil samples were collected from the plow layer (0–20 cm) and plow pan (20–40 cm) under three cornfield management scenarios: 1) conventional cropping (CK, corn straw removal and no organic manure application), 2) straw retention (SR, incorporation of 9000 kg ha− 1 chopped corn stalk), and 3) manure application (MA, 15,000 kg ha− 1 of chicken manure input). The soil samples were fractionated into three aggregate sizes, i.e., < 0.25 mm (microaggregates), 0.25–1 mm (small macroaggregates), and > 1 mm (macroaggregates). The results showed that organic amendments increased the proportion of macroaggregate and mean weight diameter (MWD), especially in the plow layer. The macroaggregates accounted for 43.87% and 49.96% of the total soil weight in the SR and MA. The distribution patterns of soil organic C (SOC), microbial biomass C (MBC), total glomalin-related soil protein (TG) and easily extracted glomalin-related soil protein (EEG) within aggregate sizes were affected by organic treatments. In the plow layer, the SOC in MA increased by 35.5% in macroaggregates compared with CK, and significant differences in MBC, TG and EEG in macroaggregates were also found among organic amendments. MWD was positively correlated with SOC, MBC, TG and EEG. Organic amendment, either through crop residues or manure application, enhanced soil aggregate stability through the positive effects on soil binding agents including SOC, MBC and glomalin-related soil protein. The links among binding agents or between binding agents and aggregate stability were aggregate scale-dependent.