Abstract: We examined the effects of N application rate and cropping pattern on the distribution of soil aggregateassociated K in a 6-year field experiment of maize monocropping, potato monocropping and intercropping of maize and potato under two nitrogen (N) application rates (low N and high N). Soil aggregates were classified using wet sieving method, and the contents of total potassium (K), exchangeable K and nonexchangeable K in each aggregate were measured. The results showed that soil aggregates were mainly composed of mediumsized aggregates (0.25-2 mm). The allocated K in mediumsized aggregates accounted for 60.6%-65.0% of soil total K reserves. The cropping pattern and N application rate significantly affected the content and reserve of aggregateassociated non-exchangeable K, but did not affect that of total K and exchangeable K. Under high N application level, intercropping significantly increased the reserves of total K and nonexchangeable K by 57.6% and 73.6% for large-sized aggregates (>2 mm), and 21.1% and 41.5% for medium-sized aggregates (0.25-2 mm), respectively, compared with the weighted average of monocropping. Intercropping increased the K uptake by maize, but reduced that of potato. Except for the potato monocropping, the proportion of exchangeable K and nonexchangeable K in aggregates (>0.25 mm) was significantly positively correlated with crop K uptake in monocropping (except for potato monocropping) and intercropping systems. In conclusion, intercropping and N application could increase the non-exchangeable K and total K reserves of larger-sized aggregates in soil, with positive consequences on the preservation and sustainable supply of soil K.

Key words: intercropping, nitrogen application rate, potassium form, aggregate.