Effects of different organic manure sources and their combinations with chemical fertilization on soil nematode community structure in a paddy field of East China

A comparative study was conducted to investigate the effects of different fertilization modes on the soil nematode community structure in a paddy field with paddy rice and wheat rotation in Jintan County(31°39'41.8″ N,119°28'23.5″ E) of Jiangsu Province,East China.Six treatments were installed,i.e.,no fertilization(CK),100% chemical NPK fertilization(F),pig manure compost plus 50% chemical fertilization(PF),straw returning plus 100% chemical fertilization(SF),pig manure compost and straw returning plus 50% chemical fertilization(PSF),and application of commercial pig manure-inorganic complex fertilizer(PMF).The soil samples were collected from the field after the paddy rice harvested in autumn.The two continuous years study showed that the soil nematode community structure varied with fertilization treatments and years.The combined application of chemical fertilizers and organic manures increased the total number of soil nematodes,decreased the abundance of soil bacterivorous nematodes,and made the abundance of predator-and omnivore nematodes increased significantly.No significant differences were observed in the abundance of soil fungivorous nematodes among all the treatments.Chemical fertilization alone and the application of commercial pig manure-inorganic complex fertilizer had no obvious suppression effect on the soil phytophagous nematodes.The abundance of soil bacteriavorous nematodes under the combined application of chemical fertilizers and organic manures was relatively increased in the second year,as compared with that in the first year,while the abundance of soil phytophagous nematodes(Hirschmanniella) was relatively decreased in the second year.From the aspect of nematode ecological indices,the Margalef diversity index(H) under the combined application of chemical fertilizers and organic manures in the second year had an increasing trend,while the NCR index had less change.The Wasilewka index had a relative increase in the second year,while the plant-parasitic index had a relative decrease.It was suggested that the application of organic manure could increase the abundance of soil microbivorous nematodes,and made the soil environment tend to be healthy.