Soil and crop response to variable-rate liming for two Michigan fields

Soil pH is known to vary spatially, making variable-rate lime application a ttractive where soil acidity occurs. This study examined the efficacy of va riable-rate lime applications based on grid sampling at various scales on s oil pH and the yield of corn (Zea mays L.) and soybean [Glycine mar L. (Mer r.)] during 3 yr, Lime was applied in two fields according to five lime man agement strategies:lime requirement (LR) estimated from maps interpolated f rom soil samples obtained from 30.5-, 61-, and 91.5-m grids; LR determined for the plot; and no lime. The LR interpolations consistently underestimate d and were not correlated with LR measured on each plot. Granulated lime, u sed to insure uniform lime application, was slow to react in the field and a lab incubation verified that it reacted much slower than agricultural lim e. Changes in pH occurred in the surface 10 cm, reflecting the depth of Lim e incorporation by chisel plowing. Corn yield did not respond to liming in 1995 and 1996. Soybean yield in 1997 increased due to liming at the Durand field, which had a lower range of soil pH values. Normalized soybean yields at both fields Followed the same linear-plateau response to pH, with soybe an yields declining below a threshold pH of about 5.9. While there is need for improvements in grid sampling design, variable lime applications under all of the grid sampling scales increased soil pH above the threshold pH fo r soybean in these fields, resulting in an improvement compared with whole field management.