Determining the role of plant-parasitic nematodes in the corn–soybean crop rotation yield effect using nematicide application: II. Soybean

Corn (Zea mays L.)—soybean [Glycine max (L.) Merr.] crop rotationis well-known to increase yields of both crops and is called the rotation effect. This study was conducted to determine the role of plant-parasitic nematodes—particularly soybean cyst nematode(SCN, Heterodera glycines), —in the rotation effect for soybean. Research was conducted at a site in Waseca, MN, that was established in 1982 to study corn–soybean rotation. Included in the study were treatments in 1 to 5 yr of SCN-susceptible soybean monoculture following 5 yr of corn, continuous SCN-susceptible soybean monoculture, and continuous soybean with SCN-resistant cultivars since 2010. Granular nematicides have been applied to half of each plot since 2010 to minimize nematode populations across crop sequences as a way to determine the role of nematodes in the rotation effect. Because nematicide was similarly effective in each crop sequence, it was not effective for determining if SCN damage varied by crop sequence. Soybean cyst nematode populations increased (P ≤ 0.05) in soybean monoculture and were negatively correlated with soybean yield (P ≤ 0.05). Pratylenchus (lesion nematode) populations decreased significantly in soybean monoculture particularly when comparing first and second year in soybean (P ≤ 0.05). Helicotylenchus (spiral nematode) and Xiphinema (dagger nematode) populations were significantly decreased in continuous soybean compared to most sequences in 5 or fewer years of monoculture (P ≤ 0.05). Trends in nematode populations suggest SCN may have had a role in the rotation effect for soybean yield, but that Pratylenchus, Helicotylenchus, and Xiphinema did not.