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The corn-soybean rotation dominates the farm enterprises in southern and southwestern Minnesota.  In much of the region these crops are grown on soils that were formed from calcareous glacial till as a parent material.  In the past, the pH of the surface soil (0 to 6 inches) was neutral or calcareous.  With repeated application of nitrogen fertilizers for corn production, the pH of these surface soils has dropped to the range of 5.5 to 6.0.  The standard recommendation would be to apply lime to these soils for soybean production.  Because of the calcareous subsoil, however, the effect of liming these soils has been questioned.  Therefore, trials have been conducted at three locations (Southern Research and Outreach Center, Jackson County, Faribault County) to evaluate the effectiveness of liming these soils for soybean production.  The results of this research are discussed separately in the following sections.

Southern Research and Outreach Center

This study was initiated in August of 1998 on a Nicollet clay loam.  Initial soil samples were collected to a depth of 48 inches and pH was measured (see Table 1).   Although acid in the depths of 0 to 6 and 6 to 12 inches, the pH rose rapidly below 12 inches.

Table 1.  Initial soil pH values at the site used for the lime study at the Southern Research and Outreach Center.

Both dolomitic (calcium + magnesium carbonate) and calcitic (calcium carbonate only) liming materials were applied.  These materials were incorporated in August.   The lime applications with incorporation were repeated in October of 2000.   Annual applications of gypsum and calcium chloride were included in this study.   Soil pH was measured in mid-summer in 2000 and 2001.  Soybean yields were measured in 1999-2001.  Soybean yields as affected by treatment used are summarized in Table 2.  Soil pH values are listed in Table 3.


Table 2.  Soybean yield (1999 through 2001 average) as affected by two liming materials and neutral salts applied at various rates.

*All treatments except for the two marked annual were applied on 9/98 and repeated on 10/00.

There was not a wide range in yields and soybean production was not affected by either the material applied or the rate of application when all treatments are considered.  When comparing the rates of dolomitic lime, however, the 1.7 bu. per acre increase from use of this source was statistically significant, but would not have been economically profitable with current prices.  In other words, the soybeans did not respond positively to the use of lime at this site.

There has been some suggestion that the use of gypsum may increase yield of crops grown on these soils.  Gypsum and calcium chloride have no direct effect on soil pH.  Use of these two materials did not increase soybean yield.  Gypsum can also be used to supply sulfur, if needed.  Since there was no increase in yield when this product was used, added sulfur was apparently not needed for soybean production. 

Table 3.  Soil pH at a depth of 0 to 6 inches as affected by the application of 2 liming materials and neutral salts.

*All treatments except for the two marked annual were applied on 9/98 and repeated on 10/10.

The pH measurements in 2000 show the impact of a single lime application in 1998.   The values for 2001 reflect the effect of two applications.  When the use of dolomitic lime is considered, pH increased as rate of application increased and this would be expected.  The low rates of calcitic lime did not produce a substantial rise in pH.   When these two sources are compared, one is not superior to the other in changing soil pH. There is, however, a substantial difference in the cost of the two materials.   Use of low rates of both dolomitic and calcitic lime had no measurable effect on soil pH.

Soil pH was the same as the control when both calcium chloride and gypsum were used.   These materials are classified as "neutral salts" and, therefore, should not be expected to change soil pH.

Trials in Jackson and Faribault Counties

The impact of lime on soybean production was also studied in the fields of cooperating soybean producers.  For the study in Jackson County, finely ground lime was applied in early spring of 1999 and incorporated with a field cultivator.  The finely ground limestone was used so that neutralization of the acidity could occur rapidly.

Finely ground limestone materials were applied in the fall of 2000 at the Faribault County site and incorporated with a field cultivator the following spring.

Soil samples were collected to a depth of 60 inches prior to planting and the results are summarized below.

As was the case at the site at the Southern Research and Outreach Center, soil pH increased with depth.  Below 12 inches, the pH  rises to near  neutral then increases substantially with depth.

Calcitic lime was applied at two rates and one rate of dolomitic lime was used.  The calcitic lime had 1613 lb. of Effective Neutralizing Power (ENP) per ton while the analysis of the dolomitic lime showed 1631 lb. (ENP) per ton.  These values are very close.  Therefore, one ton per acre of calcitic lime should produce the same results as one ton per acre of the dolomitic material.

The measured yields are listed in Table 4.  In both fields, application of both liming materials had no effect on soybean yield. 


Table 4.  Soybean yield as affected by lime source and rate of application.

There are differences in yields shown in the table.  These differences, however are not statistically significant.  Considering the cost of lime, either much larger increases in yield or continued long-term responses would be required to pay for the lime.

A consideration of the results from both studies leads to the conclusion that application of lime is not a profitable management practice for soybeans grown on soils that were formed from calcareous glacial till.  It is important to recognize, however, that many Minnesota soils were formed from parent material that is not glacial till.  The subsoil for this soil is frequently acid.  Lime should be an important component of the management package for soybean production on these soils which have acid subsoils.