This research aimed to use saturation kinetic models to evaluate plant responses to fertilization, and possible interactions among nutrients in the efficiency of nutrient use in crop production. Data of soybean (Glycine max), wheat (Triticum aestivum), cotton (Gossipium hirsutum), and bean (Phaseolus vulgaris) responses to nitrogen, phosphorus or potassium fertilization showed hyperbolic curves and followed a Michaelis-Menten relationship. The data were evaluated by Lineweaver-Burk data transformation in order to obtaining the kinetic constants kmax (theoretical maximum performance) and ks (amount of nutrient needed to reach half theoretical maximum performance). The effect of a second factor (limestone, nitrogen or phosphorus) in changing the kmax and ks of the first nutrient under evaluation were also analyzed. A second nutrient increases the efficiency of the first nutrient under evaluation, by increasing kmax without or with increase in ks, or by decreasing ks. In both situations, the highest efficiency of use of nutrient happens at low-level fertilization. Although maximum crop productivity is always desirable, it demands elevated levels of nutrients, but the efficiency of nutrient use decreases drastically as the level of the nutrient increases, especially when ks is low. In addition, elevated levels of fertilizers in agriculture leads to exhaustion of nonrenewable natural resources and environmental pollution, such as water contamination with nitrate, soil acidification and emissions of CO2 and N2O to atmosphere, with deleterious effects on global warming.