Abstract: A fully 2×4 factorial experiment was conducted with four levels of nitrogen fertilization amendments, i.e. decreasing the nitrogen amendments from a routine amount 300 kg N·hm^-2 to 10%, 20% and 40% of the routine amount, respectively, with conventionally continuously flooded irrigation or controlled non-continuously flooded irrigation. Across all the eight treatments, there were 16 families and 28 genera of soil nematodes, belonging to 7 families and 12 genera of bacterivores, 3 families and 4 genera of fungivores, 3 families and 5 genera of plant-parasites, and 3 families and 7 genera of omnivore-predators, respectively. Among all the nematodes, the genus Filenchus was dominant with a relative abundance of 35.4%-47.9%. Regarding the nematode trophic groups, the fungivores accounted for the highest proportion of soil nematodes, followed by bacterivores as the second, and then the plant-parasites, and the omnivore/predators at the minimum. The total nematodes under the conventionally flooded irrigation were slightly higher than under the controlled non-continuously flooded irrigation. When reducing the nitrogen amendment to 80% of the routine application rate (i.e. 240 kg N·hm^-2), the total number of nematodes increased significantly, but no further changes were found when even less nitrogen was amended.

Key words: total nitrogen, available nitrogen, simulated grazing, biological soil crusts, microbial biomass nitrogen.