The stability mechanism for organic carbon of aggregate fractions in the irrigated desert soil based on the long-term fertilizer experiment of China

Abstract

Soil samples from the Hexi Corridor located in the arid regions of Northwestern China were collected from a 24–year–old field experiment. The distribution of organic carbon (OC) in the different size water stable aggregate (WSA) fractions and the stability mechanism of OC in WSA size fractions were studied. The results showed that long-term application of solo organic manures or in combination with inorganic N fertilizer significantly increased the OC concentrations of different size WSA fractions compared to the CK, while long-term application of solo N fertilizer had no significant effect. After fertilization for 24 years, the OC concentrations of 0.25–2 mm WSA fraction was significantly positively correlated with the percentages of this WSA fraction, while the OC concentrations of >2 mm, 0.053–0.25 mm and <0.053 mm were not significantly correlated with their corresponding percentages of WSA fractions (P > 0.05). In addition, the OC concentrations of loosely, stably and tightly bound humus in 0.25–2 mm WSA fraction were significantly higher than those in other size WSA fractions, which were also significantly correlated with the corresponding chemical components, e.g. different forms of calcium, in 0.25–2 mm WSA fraction (P < 0.05). It could be explained that affinities of OC to chemical components in 0.25–2 mm WSA fraction were stronger than those in other size WSA fractions. The results of NMR analysis also showed that the aromaticity and alkyl/O-alkyl ratio for the 0.25–2 mm WSA fractions were significantly lower than those for other size WSA fractions (P < 0.05). These results demonstrated that the 0.25–2 mm WSA fraction played an important role in stabilizing soil OC and protecting OC from degradation in the irrigated desert soil.