The vertical distribution of the dominant genera of plant nematodes at the depth of 0-150 cm of an aquic brown soil were studied for four land use patterns, i.e., paddy field, maize field, fallow field and woodland in the Shenyang Experimental Station of Ecology, Chinese Academy of Sciences in November of 2003. The results showed that the numbers of some dominant genera under different land uses decreased with the increase of soil depth. Helicotylenchus was most dominant genus under each land use type. Genera of Filenchus, Psilenchus and Tylenchus in paddy field occurred at the depth of 0-20 cm; while Paratylenchus in fallow field and woodland, as well as Pratylenchus in maize field presented in the deeper soil layers (0-80 cm). Significant correlations between the numbers of dominant genera of plant nematodes and soil chemical properties were found in this study. The number of Helicotylenchus under different land uses was positively correlated with C/N ratio, total C, total N, total P, alkai-N, and Olsen-P. The numbers of Filenchus and Paratylenchus in paddy field, Pratylenchus in maize field and Paratylenchus in fallow field were negatively correlated with soil pH, and positively correlated with total C, total N and alkai-N. This study results showed that it is essential to sample at a certain depth according to the vertical distribution information of different genera of plant nematodes in adequately assessing the population size of plant nematodes.
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