Long-term manure application enhances the stability of aggregates and aggregate-associated carbon by regulating soil physicochemical characteristics

The response to climate change through soil organic carbon sequestration has received increased interest. While soil organic carbon sequestration is related to the stability of aggregates and aggregate-associated carbon and varies among fertilization practices, little information is available on how fertilization practices impact the stability of aggregates and aggregate-associated carbon in alkaline soil. Using a 13-year field experiment with three replicate plots of four fertilization practices (only chemical fertilizer application, only manure application, 50% chemical fertilizer and 50% manure application, and 100% chemical fertilizer and 100% manure application) and one control treatment (nonfertilization), we investigated the correlations between 20 soil physicochemical factors and stability indices of aggregates and aggregate-associated carbon under the influence of long-term fertilization. Fertilization with manure not only significantly improved soil physicochemical characteristics, such as increasing conductivity, the cation exchange capacity, organic carbon, and the availability of nutrients and calcium/magnesium, but also enhanced mean weight diameter, geometric mean diameter and large aggregate- and microaggregate-associated carbon. Soil organic carbon was more abundant in large aggregates and microaggregates than in other fractions, and the carbonyl group bands in large aggregates were wider than those in other fractions. Mean weight diameter, geometric mean diameter and large aggregate- and microaggregate-associated carbon were positively correlated with the total amounts and availabilities of soil nutrients and free and exchangeable calcium/magnesium and were negatively correlated with soil pH, likely because fertilization with manure enhanced the stability of aggregates and aggregate-associated carbon by increasing the availability of soil nutrients and calcium/magnesium ions, while high pH limited the stability of aggregates and aggregate-associated carbon. Strategies aiming to improve alkaline soil and increase soil C stocks may thus focus on manure or fertilizer application with the ability to reduce soil acidity.

Automated summary

The study investigates the impact of different fertilization practices on soil aggregate stability and aggregate-associated carbon in alkaline soil. Results show that manure application improves soil physicochemical properties and enhances the stability of aggregates and aggregate-associated carbon, while high pH restricts their stability. Strategies to improve alkaline soil and increase soil carbon stocks may prioritize manure or fertilizer application to reduce soil acidity.