Thirty-six soil samples collected from 24 sites were used to investigate the relationships between cation-ratio concepts and sufficiency level approaches in plant nutrition. Based on threshold values, about 25.0% of the soils had calcium:magnesium (Ca:Mg)-ratio fallen outside the favorable range, despite the sufficient levels of individual elements in soils, violating the base cation ratio concept. Similarly, 63.0% of soils had potassium:magnesium (K:Mg)-ratio falling in the unfavorable range for K uptake, though the individual element K was found to be above adequate in all sites/soils. In 29.0% of soils (Mg:K)-ratio is rated unfavorable for nutrients’ uptake, as directly related to sufficiency level concepts. Likewise, all soils had the % K:TEB (total exchangeable bases)-ratio falling within the suggested favorable range for most tropical crops, favoring the two concepts. With respect to Ca:TEB ratios, 79.0% of soils were considered unfavorable for Mg and/or K uptake, implying that the lower the base saturation, the more favorable the conditions for the aforementioned nutrients uptake and vice-versa. This is also against the base cations’ saturation ratio concept because all soils in those sites had low levels of Ca and Mg. In conclusion, therefore, from such contradictory information those generated the validity of the base cations’ ratio concept needs further detailed investigation.

Keywords: Potassium, calcium, magnesium, ratios, fertilizers, rhizosphere