In rice-based rainfed lowland ecosystems in Northeast Luzon, Philippines, intensive cropping systems with rice in the wet season and a cash crop in the dry season are commonly adopted. The introduction of a nitrogen (N) catch crop during the dry-to-wet transition period is expected to reduce N pollution of the groundwater which is resulted from excessive N application for cash crop cultivation. In this study, the root distribution of N catch crops and the performance of succeeding rice in terms

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... of root growth and N use efficiency were investigated. Among the N catch crops tested, root length density at the 0•'20 cm surface was relatively higher in maize than in indigo and indigo+mungbean intercropping. Below 20 and down to 70 cm depth, all the three crops showed an almost uniform root length density along the depth, reflecting the high capacity to trap leaching NO3 from the deep soil layer as N catch crops. In succeeding rice planted in the wet season, root growth was stimulated in the surface and subsoil by previous planting of catch crops, indigo and maize, compared with rice planted after fallow. Root-shoot ratio increased after catch crop cultivation compared with chemical N supply after the fallow. N use efficiency for grain production was also improved in the treatment with the catch crops compared with that in the treatment with chemical N supply. The results indicate the importance of underground root interaction between rice and other component crops in this ecosystem.