Last year 53% of the samples sent to the Penn State Ag Analytical Services Lab were below optimum in pH and 27% were below pH 6.0. As part of a successful crop management plan, liming programs should be given the same priority as our fertilization and pesticide programs.
A common question is when is the best time to lime? The bottom line is that anytime the soil conditions are appropriate for the spreading equipment and the crop does not limit spreading, is okay. However, there are some helpful considerations for when to apply limestone. First, lime on a regular basis. If soils are regularly limed so that the pH never gets too low, then the timing of maintenance liming is not very critical. Thus, regular liming provides maximum flexibility to lime when you have time and the conditions are right. In our soils liming every 3-4 years will usually meet this goal. This also fits with our normal soil testing frequency.
Second, plan ahead. Even very high quality limestone takes some time to react and correct the acidity in the soil. Applying limestone at least 6 months ahead of when the desired pH is needed, is a good guideline. This is especially important if the soil pH is very low. For example, if a new alfalfa seeding is planned liming should be considered the year before seeding or at least the fall before seeding.
Finally, consider the soil conditions. The main concern here is compaction from heavy lime trucks. For timing a limestone application within the year, the ideal would be to apply limestone on a dry soil. Another alternative is to apply limestone on a frozen soil to minimize compaction. There are no problems with applying limestone on a frozen soil as long as the limestone stays where it is applied. The main thing here is not to apply limestone on a frozen soil where it might be directly washed off of the field by winter rains or snow melt. This would be sloping fields, especially with little or no cover. Actually, if limestone is applied to a frozen soil or on a dry soil in the fall, there will likely be some shallow incorporation due to freezing and thawing action throughout the winter. This can be helpful in no-till or perennial crops where there will be no tillage to mix the limestone with the soil.
One word of caution is that sometimes there can be tire track damage to alfalfa stands from lime trucks even on frozen hay fields. Another issue is that, just like fertilizer and pesticides, limestone must be spread evenly to be effective. This can be a problem for field dumped limestone that might be spread by farmers. First, manure spreaders generally are not very good at uniformly spreading limestone. Also, if these piles freeze, the limestone can be very lumpy resulting in non-uniform application and uneven pH across the field. The bottom line is that liming must be a priority in crop management, and anytime is a good time to lime, including winter, as long as you pay attention to a few important details.