Potato Nitrogen Response and Soil Microbial Activity as Affected by Fumigation

In North America, potato early dying is often controlled using soil fumigants. Fumigants confer benefits on plant health but also impact soil microbial activity, including nitrogen (N) cycling. The purpose of this study was to evaluate the effects of two soil fumigants, chloropicrin and metam sodium, on potato crop yield, N uptake, and N use efficiency (NUE), as well as soilborne pathogens, soil microbial respiration rates and soil concentrations of NH₄⁺-N and NO₃⁻-N. We established a field study with a split-plot randomized complete block design in 2016 and 2017, with whole plots divided among three fumigation treatments (no fumigant, chloropicrin, or metam sodium) and split into five subplots, each receiving a different total application rate of N (45, 135, 202, 269, or 336 kg·ha⁻¹ N). Both fumigants suppressed Verticillium dahliae propagule concentrations and foliar symptoms of potato early dying while increasing yield, final tuber set, N uptake, and NUE. Fumigation did not affect the agronomic optimum N rate, nor the response of marketable yield to N rate, but it did increase yield per unit N applied (partial factor productivity) by 16% and 35% over the non-fumigated controls in 2016 and 2017, respectively. Chloropicrin, but not metam sodium, reduced the prevalence of common scab symptoms in tubers. Both fumigants decreased microbial respiration rates before planting and at midseason. Fumigants reduced nitrification rates before planting and at midseason, with chloropicrin having a particularly strong effect before planting. While fumigation conferred benefits to yield and NUE, its effects on microbial community structure and function merit further study.