Investigation of the effects of some agricultural fertilizers on entomopathogenic nematodes

Entomopathogenic nematodes (EPNs) are used in biological control because they can infect harmful insects living in the soil, can be mass produced and formulated, exhibit long-term efficacy and are harmless to non-target organisms. EPNs are obligate endoparasitic organisms that pass more than 90% of their life cycle in the insect pest. Within the soil, there are many factors that affect the vital activity and permanence of EPNs. Some agricultural activities such as fertilization, tillage and irrigation, can positively or negatively affect the activities of EPNs inhabiting the soil. Especially long-term and excessive use of the inorganic fertilizers originated from N, P and K lead to various environmental problems such as soil salinity and heavy metal accumulation. One of the best methods to improve the physical and chemical structure of soils is the addition of organic fertilizers. The possibility of a positive or negative interaction between fertilizers and EPNs that share the same environment is important for biological control. In this study, 2 different EPN strain (Steinernema feltiae TUR-S3, Heterorhabditis bacteriophora HBH) and 10 different fertilizers were used to determine the effect of fertilizers on EPNs. At least two different doses have been determined for each fertilizer, based on the form in which the fertilizers are applied to the field and the recommended amount per decare. In general, the organic fertilizer which contain humic and fulvic acids supported EPN's persistance, while some inorganic fertilizers (DAP, NP, NPK) used in the study increased the mortality rate of EPNs. It was also found that TUR-S3 is more resistant to inorganic fertilizers than HBH.