Potassium dynamics in root-zone and non root-zone in yellow cinnamon soil with paddy-upland rotation

Potassium dynamics in the root-zone and the non root-zone in yellow cinnamon soil with a rapeseed-rice rotation system was studied through a rhizobox device to provide evidence for research on soil K supplying mechanism and reasonable control of rhizosphere nutrition. The results show that soil water soluble K and exchangeable K in the root-zone are reduced at early stage of rapeseed growth under the rapeseed-rice rotation. Along with rapeseed growth and K uptake, soil non-exchangeable K in the root-zone also decreased significantly. Soil water soluble K in the inner (0-20 mm), middle (20-40 mm) and outer (40-60 mm) parts of the non root-zone are moved forward to the root-zone. Soil exchangeable K and non-exchangeable K are transformed to water soluble K and decreased gradually. In the early stage of rice growth, water-log cultivating practice promotes the diffusion of soil water soluble K from the non root-zone to the root-zone and transition of exchangeable K to water soluble K. Along with the growth of rice and more K uptake, soil non-exchangeable K in each part is decreased significantly, while soil water soluble K and exchangeable K are not decreased. These results indicate that K uptake by crops is mainly contributed by the root-zone, and K in the non root-zone can be moved to the root zone gradually depending on the distance. Within the rotation system, soil non-exchangeable K is the main potassium source, followed by soil exchangeable K and water soluble K.