Objective  Correlation between the root-knot nematode disease on cucumber plants and the fertility of soils at different depths was investigated in a greenhouse to optimize the disease control.

  Method  Soil fertility indicators including pH, available nitrogen, available potassium, total phosphorus, total nitrogen, and organic matters from surface to 30cm in depth during various cucumber growth stages were compared with occurrence of root-knot nematode disease on the plant for possible correlations.

  Result  The available nitrogen, available potassium, and total nitrogen in the upper-layer of the soil were higher than those in the middle- or lower-layer in 128 d, 188 d, and 218 d after planting, with a statistic significance at P_0.05 level. Significant correlations were found on the total phosphorus, available potassium, available nitrogen, and pH, but not on the total nitrogen, in the soils at different depths. The total phosphorus in soil significantly inversely correlated to the disease on the cucumber plants with a correlation coefficient of −0.842 for the upper-layer, −0.854 for the middle-layer, and −0.869 for the lower-layer. On the available nitrogen, an inversed correlation was found between that in the upper-layer and the disease on the plants with a coefficient of −0.562. No significant correlation existed between the disease and the available potassium and pH relating to the upper-layer soil.

  Conclusion  The total phosphorus and nitrogen in the soil highly correlated with the root-knot nematode disease and were considered relevant in preventing and controlling the disease on cucumbers.