Effects of fertilizer, nematicide, and tillage on plant–parasitic nematodes and yield in corn and soybean

Soybean cyst nematode (SCN, Heterodera glycines) is the most damaging pathogen of soybean [Glycine max (L.) Merr.] in the United States and plant–parasitic nematodes such as Pratylenchus (lesion nematode) and Helicotylenchus (spiral nematode) commonly infect corn (Zea mays L.). There are few management options for these nematodes, so understanding how common agronomic practices affect these nematodes is critical. Therefore, a series of 2-yr experiments were conducted in corn and soybean production. Long-term conventional tillage (CT) and minimum tillage (MT) treatments were in place at the study site. Fertilizer and granular nematicide—for assessing crop damage by nematodes—treatments were applied: (i) untreated control, (ii) NPK, (iii) NPKS, (iv) liquid swine manure, (v) nematicide without fertilizer, and (vi) NPKS with nematicide. Lesion nematode and SCN densities were greater in MT than CT during portions of the study, but tillage did not affect spiral nematodes. Corn yield was 8% greater in CT than MT in the first phase of the rotation, but tillage did not significantly affect soybean yield. None of the fertilizers— manure, NPK, or NPKS—reduced plant–parasitic nematode densities compared to control. Manure consistently increased corn and soybean yields. The NPK and NPKS were beneficial for corn, but inconsistent for soybean yields. There was some evidence that soybean yield response to fertilizers was greater in more stressed environments, such as with more SCN pressure. Because nematicide efficacy was inconsistent, it was not possible to make a definitive measurement of crop damage by plant–parasitic nematodes in this study.