Potato Grower

WWW.POTATOGROWER.COM 31 metam sodium than in non-fumigated control plots. The use of either fumigant also increased the amount of yield produced per pound of nitrogen applied. All of these differences reflect the differences between treatments in tuber yield (biomass) described in the previous paragraph. They were not due to differences in tuber nitrogen concentration or the amount of nitrogen present in the vines just before vine kill. Not a Magic Bullet While chloropicrin and metam sodium both provided benefits in terms of disease control, yield, and nitrogen use efficiency, their effect on microbial activity outside of pathogens was generally negative. Based on CO 2 emissions from the soil, which are strongly related to microbial activity, both fumigants suppressed overall microbial activity before planting and at midseason. The effect was no longer detectable after harvest. In the pre- planting sample, metam sodium's effect was especially strong. Plots treated with either fumigant had higher soil ammonium concentrations than the non-fumigated control plots at planting and midseason. This indicates that soil microbes did not convert ammonium to nitrate efficiently under fumigation; this effect was especially strong when chloropicrin was the fumigant. So, in addition to suppressing microbial activity generally, fumigation slowed the rate of nitrogen cycling in the soil. What Actually Works? Our results show that, while soil fumigation with metam sodium or chloropicrin is beneficial to the potato crop in the short term, a side effect is a decrease in soil microbial activity and altered nitrogen cycling. How this affects soil health is uncertain, and it will take a longer-term study to find out—one looking more closely at soil health and the microbial community. It is also important to consider other avenues for controlling soil-borne pathogens, especially if chemical fumigants are found to be detrimental to soil health in the long term. Are there other viable options for growers to control soil-borne pathogens? Could fumigation be used less frequently or in combination with inoculation of beneficial microbes? Maintaining soil health is essential to the long-term survival of a farming operation, but strategies to promote soil health must not be so costly that they compromise the farm's viability in the short term. To address these issues, we are collaborating with researchers across the country in a multi-state investigation into how soil health is affected by management decisions in potato cropping systems, whether methods for improving soil health work well in these systems, and how planting and incorporating biofumigant cover crops such as mustard compare with chemical fumigation in promoting yield and suppressing disease. This Specialty Crop Research Initiative- and USDA/ NIFA-funded project is in its fourth year, and the year when we will get at fewest preliminary answers to these questions. Enhancing soil health is a slow and complex process, particularly with a challenging crop like potatoes. Therefore, this study will need to be extended beyond 2022 to learn whether effective strategies continue to improve soil health while controlling soil-borne pathogens over multiple rotations and years. This research was supported with funding from the Minnesota Area II Potato Council, Minnesota Agricultural Fertilizer Research & Education Council, and TriEst Ag Group, Inc. Results were published in the American Journal of Potato Research September 2021. Study authors include James Crants, Carl Rosen and Linda Kinkel at the University of Minnesota; José Pablo Dundore-Arias at California State University, Monterey Bay; and Andy Robinson and Neil Gudmestad at North Dakota State University. PG

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