Issue link: http://read.uberflip.com/i/1159622
30 POTATO GROWER | SEPTEMBER 2019 New insights into outdated assumptions about metam sodium movement in soil Looking Deeper Diggin' In Diggin' In FUMIGATION | By Kyle Coleman Many potato growers are sub-optimizing results from their applications of metam sodium because of outdated assumptions regarding the importance of pre-application soil preparation and a lack of understanding about how the product travels through the soil. Team members at NovaSource, the crop protection business unit of Tessenderlo Kerley, Inc. (TKI), have recorded several noteworthy findings while conducting more than 20,000 post-metam sodium application soil sample readings with a photoionization detector (PID). Readings were taken in a variety of soil types at 20 locations in seven states from Washington to Florida during a period of more than two years from August 2016 through early 2019. The observations were not part of a formal scientific study. However, each of the 20 cooperators who allowed their fields to be sampled for the presence of metam sodium at different soil depths during the hours and days following application made changes to their product application methods upon seeing data collected in their fields. Key observations were based upon a renewed understanding of the limited mobility of metam sodium when applied in soil, including: • Its propensity to move just 6 inches above and below a single injection point; • Differences in soil preparation playing an important role in facilitating product movement; • Different application methods resulting in different movement patterns in the soil; • The importance of soil moisture in product movement and sealing the product; and • Precision placement of metam sodium being necessary to maximize effectiveness of suppressing weeds, disease and nematodes In order to perform at peak effectiveness, metam sodium needs to come in contact with the pest to control it. Effective depths are different for weeds, diseases and nematodes. Soil fumigants have unique properties that enable them to work at various depths. For decades, a common assumption has been that all fumigants move through the soil easily and equally. Methyl bromide has the ability to penetrate a hardpan, while metam sodium, with a far lower vapor pressure, does not. Observations recorded by NovaSource showed that metam sodium mobility is particularly weak in the 0-to-4-inch range when applied by shank, especially if the soil surface is dry. Even when chemigated, metam sodium had difficulty reaching depths greater than 4 inches. Further, regardless of application method, lateral movement was found to be limited, even in sand, and downward movement was also observed to be limited by hard or compacted soil. Cooperators working with NovaSource generated highly favorable results by experimenting with multiple methods of soil preparation. Metam sodium movement was maximized in soil that was moist, friable and mixed. Upon experimenting with different application methods, each of the cooperators confirmed the importance of moisture in the soil to facilitate movement and sealing of the product. Cooperators' experiments into developing different depths of shank applications also showed favorable results. For example, in 80 percent soil moisture, post-application metam sodium readings in shank-applied applications consistently increased as much as 25 percent when compared against 50 percent soil moisture. Pre-moisture acts as a foundation for setting up the entire fumigation process. Moist soil is observed to both facilitate product movement and help