Effects of intercropping and drought on soil aggregation and associated organic carbon and nitrogen

Drought has significant effects on soil physicochemical properties and thereby crop productivity. Intercropping is a traditional agricultural practice with a good ecological effect and can improve soil structure. However, the effects of intercropping on soil aggregate distribution and associated organic carbon (OC) and nitrogen (N) compared with monoculture under drought remains unclear. Therefore, a two-year controlled rainfall field (i.e., 30-40 days of 100% rainfall reduction during crop growth) was carried out to examine the effects of intercropping and short-term drought on soil aggregate stability and associated OC and N in Northeast China. Results showed that soil OC and N were predominant in macroaggregates (2-0.25 mm), accounting for 39%-51% of SOC, 36%-51% of N at 0-10 cm depth, and 44%-67% of SOC, 43%-66% of N at 10-20 cm depth. After 2 years of a rainfall reduction treatment, large macroaggregates (>2 mm) increased by 84.7% at 0-10 cm and the aggregate stability improved. There was no difference in the mass of aggregates between monoculture and intercropping, but short-term drought increased >0.25 mm aggregates and stability in intercropping soil at 0-10 cm depth. Moreover, drought significantly increased bulk soil OC in 10-20 cm but decreased the OC and N concentrations in large macroaggregates and silt + clay fractions (<0.053 mm) in 0-10 cm. Compared with the monoculture, intercropping enhanced OC and N concentrations in aggregates, and decreased soil C/N ratio. Therefore, these findings provide insights into how intercropping and short-term drought interactively influence soil aggregation, and C and N processes.