Watch for pH problems in older asparagus fields

Noticing some thin spots in your older asparagus fields? Check to make sure the pH hasn’t dropped in those spots.

Most commercial asparagus growers have their fields on a regular soil-testing program. Usually that is once every two years, but is sometimes yearly. Unfortunately, even when growers are regularly soil testing and following the soil test recommendations, pH problems can develop as fields age.

The wide spread use of the no-till system of production can speed development of pH problems in asparagus fields. Most nitrogen fertilizers are acid-forming by nature and in no-till systems where these materials are applied to the surface once or twice per season, acid layers can develop in the 2- to 3-inches below the surface (see Michigan State University Extension Bulletin E-471, “Lime for Michigan Soils”).

Another cause of rapid development of low pH spots in asparagus fields is the sandy texture of soils planted to the crop. The pH drops more quickly in sandier, lower organic matter soils (see MSU Extension Bulletin E-498S, “Sampling Soil for Fertilizer and Lime Recommendations: Frequency of Soil Sampling”). Where the texture varies within a field, look for pH problems to develop first on the sandiest spots.

Growers often notice that asparagus fern growing on these sandier spots is shorter and that there are fewer ferns per crown. Developing pH problems are often easiest to notice from a high-boy type of sprayer. If the person in charge of spraying is not also the person in charge of soil testing, it may make sense to have the soil testers ride the sprayer once during fern season to spot these problems. Flagging tape or GPS positioning units can be used to mark these problem spots, and separate samples should then be taken to check the pH of the problem spots.

Another, more expensive way, to identify these spots is to employ precision farming techniques where samples are taken on small grids, or in small zones, decreasing the chances of missing isolated pH problems. Once the low pH spots have been identified, separate lime applications can be made to these problem spots.

It is better to detect isolated pH problems early. Asparagus is a no-till crop in most of Michigan, and lime is applied to the surface and not incorporated after application. This means that to bring up pH after it has dropped will take longer because rainwater or irrigation must solubilize and move the lime into the soil, which is a slower process than when lime is incorporated.

For more information about soil pH and soil sampling, consult the following bulletins and articles.

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