Evaluation of the Magnesium Soil Test Interpretation for Peanuts1

Abstract

Abstract Decreasing concentrations of extractable Mg in soils of peanut (Arachis hypogaea L.) production regions of North Carolina have resulted in increased Mg fertilizer recommendations. There is little soil or plant criteria, however, on which to base Mg deficiency. The objective of this study was to determine the yield and Mg status of peanuts relative to the level of soil Mg. Five counties were surveyed for leaf and soil data in 1989–90. Similar data were available from nine counties in 1970–72. A field experiment was also conducted in 1989–90 in an on-going lime and Mg study. Although the 1990 survey data suggested that phosphogypsum usage during the last decade may be reducing Mg levels in the surface soil, leaf Mg was almost invariably above 2.0 g kg-1 for both surveys, reflecting adequate amounts of soil Mg according to current plant analysis standards. In the field study, prior lime and Mg treatments resulted in soil Mg ranging from 0.02 to 0.25 cmolc L-1, but there was no yield response that could be related directly to Mg. Leaf Mg was positively correlated to surface soil Mg, and inclusion of subsoil Mg slightly improved this relationship. The data from these studies indicated that sufficient leaf Mg (above 2.0 g kg-1) was attained when surface soil Mg was as low as 0.06 cmolc L-1 or as low as 3 percent of the CEC. We feel these estimates of the soil Mg critical level for peanut production are high, as there was not a Mg deficiency with leaf Mg as low as 1.5 g kg-1 in the field study.