We seem to have more questions this winter related to liming of soils. Spreading of lime when soils are frozen eliminates compaction issues, but could pose other challenges as we enter the 2010 cropping season. Potential for loss of any crop fertilizer (including lime) due to run off from frozen ground is a genuine concern on sloping soils, particularly those without any crop residue on the surface.

Application of lime in late summer or fall allows the neutralizing power of the product 6 or more months to bring up the soil pH. When lime is spread on frozen fields, the process of pH adjustment does not actually begin until warmer weather thaws the soil, thus permitting the lime particles to dissolve and enter the topsoil surface. If spring tillage is planned, the mixing of the soil distributes the lime in the top several inches.

In a no-tillage situation, applying large amounts of lime can result in fairly rapid and substantial increases in soil pH at shallow soil depths. Although the lime eventually moves deeper into the soil profile, and the pH at the soil surface equilibrates and decreases somewhat, the temporary increase in pH can have consequences for the persistence and activity of herbicides applied this spring. A number of herbicides can be more active as soil pH increases above 7, including atrazine, metribuzin, and chlorimuron. Increased activity can be a good thing relative to weed control, but can also increase the risk of crop injury where other factors are favorable for injury to occur.

Mark Loux, Ohio State University Extension weed specialist warns farmers that increased carryover risk at high pH is the more important issue. A primary caution is to possibly avoid use of chlorimuron-containing herbicides, (Canopy, Cloak, Valor XLT, Envive, Enlite) where lime was applied this winter and the pH at the soil surface is above 7. The first several months after herbicide application are important for herbicide degradation. Degradation of chlorimuron will be inhibited at the high pH that can result from liming, and lack of substantial degradation during these first few months increases the carryover risk.

Statements from herbicide labels regarding high soil pH include the following:

Isoxaflutole (Balance Flexx, Corvus, Prequel) labels indicate the high soil pH is one of the conditions that can increase risk of crop injury.

Hornet, Python, SureStart do not apply where soil pH is greater than 7.8 Metribuzin (corn) do not apply where soil pH is 7.0 or greater
Authority Assist within a rate range for a given soil type, use the lower rates where soil pH is greater than 7  Authority MTZ do not apply to soils with pH greater than 7.5 Metribuzin (soybeans) injury risk increases where soil pH is more than 7.5.

The 2010 Weed Control Guide for Ohio and Indiana is an excellent resource to help determine concerns you might note if liming has or will occur before spring planting, and no incorporation is planned. Two pages in the bulletin also provide recommendations on over 80 herbicides in respect to crop rotation restrictions. A number of those restrictions are directly related to pH levels.

Purchase a copy at any OSU Extension County office, call 614-292-1607 for a copy or check on line http://agcrops.osu.edu/weeds/documents/2010WeedControlGuide.pdf

The views and opinions expressed in this column are those of the author and not necessarily those of Farm World. Readers with questions or comments for Roger Bender may write to him in care of this publication.