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Basic Cation Saturation Ratios as a Basis for Fertilizing and Liming Agronomic Crops. II. Field Studies¹

A field experiment was conducted over a period of six cropping years to determine the relative merits of basic cation saturation ratio (BCSR) and of sufficiency level of available nutrients (SLAN) as bases for a p plying lime (Ca and Mg) and fertilizer K for crops. The study involved an acid Loudonville silt loam soil (Ulfic Hapludalf, fine-loamy, mixed, mesic) which had been adjusted to 3 pH (Ca), 3 Mg, and 2 K levels, in all combinations. The sequentially grown crops were: corn (Zea mays L.), corn, soybeans (Glycine max L. Merr.), wheat (Triticum aestivum L.), alfalfa (Medicago sativa L.), and alfalfa. The treatment variables for pH were: 5.0, 6.0, and 6.5; for percent Mg saturation of soil CEC were: 4, 6, and 10; and for percent K saturation of CEC were 2.4 and 4.3. Both yields and crop compositions were measured. The treatment variables resulted in an average soil Ca/Mg ratio range of 2.3 to 26.8 and an average soil Mg/K ratio range of 0.6 to 3.6. Direct correlation or association of crop yields with basic cation saturation ratios (BCSR) were quite low. Also, the treatments producing the five highest yields for each crop gave rather wide ranges in both Ca/Mg and Mg/K ratios which were to a large extent also common to those ratios associated with the five lowest yielding treatments. Thus, finding no evidence to support the validity of the BCSR concept as a basis for providing maximum crop yield conditions, the direct response of the crops to the basic nutrient cations (SLAN) concept was examined. Although yield responses to increased levels of the cations were not obtained in all cases, the results obtained were reasonable; and compositions of Ca, Mg, and K were in almost all cases increased as the levels of the respective cations were increased. The results strongly suggest that for maximum crop yields, emphasis should be placed on providing sufficient, but nonexcessive levels of each basic cation rather than attempting to attain a favorable BCSR which evidently does not exist.

Key Words: Sufficiency level of available nutrients • Soil test ratios for calcium, magnesium, and potassium • Crop responses

² Professor, research associate, assistant professor, and Emeritus professor (G.B. Triplett, 114 Kirkside, Starkville, MS 39759), respectively.

Received for publication September 7, 1982.