Nematode communities and macronutrients in composts and compost-amended soils as affected by feedstock composition

Farm composts were produced from selected feedstocks and compared to one external farm compost and one green waste compost. Nematodes were omnipresent in the composts (on average 26 ind./g dry weight compost) and many taxa were common to all composts (i.e. Mononchoides composticola,
Diploscapter coronatus, Halicephalobus gingivalis, Ditylenchus sp., Diplogaster sp., Diplogastrellus sp. and Diplogasteritus sp.) and occurred in similar proportions. Composts with a somewhat different species composition or proportion also displayed differences in the abiotic parameters, suggesting that compost maturity and status may be reflected by the nematode community. Significant differences (ANOSIM, p = 0.001) in nematode community between the farm composts and the green waste compost were found. Nevertheless, despite largely different feedstock materials and proportions, and despite clear differences in chemical properties and stability of the composts, biologically very similar composts were produced. The 11 composts of different composition were further tested in an incubation experiment to investigate their short-term effect on the existent soil nematode community and on the soil chemical properties. Therefore, the nematode community together with several abiotic parameters (pH, EC, DM, OM, Ptot, C/N, and NO3/NH4) of the used composts and the soils before and 12 weeks after compost amendment, were analyzed. All compost amendments resulted in a significant pH increase in the soil (one-way ANOVA, p < 0.01), and differences in plant-available macronutrients in the soil between the applied composts were detected. The changes in soil chemical properties after compost addition were related to the compost type and could be linked to the properties of the used feedstock materials. After 12 weeks of incubation, the nematode numbers in the soil increased, except in soil amended with the green waste compost. In particular, the abundance of the fungal-feeding Ditylenchus increased significantly (one-way ANOVA, p < 0.03) in all soils amended with farm compost. This increase may well be purely caused by the addition of nematodes present in the compost.