Nutrient transport towards root surface can be accomplished by mass flow or by mass flow and diffusion, depending on the activity of the nutrient in the soil solution, and on the nutrient demand of the plant. The objective of this greenhouse experiment was to verify the contribution of the mechanisms of mass flow and diffusion for supplying potassium, calcium and magnesium to rice plants. Samples of a clayey Oxysol were treated with Na2CO3, K2CO3, CaCO3 and MgCO3 as amendments. Seventy-five days after planting, the amounts of dry matter, potassium, calcium and magnesium accumulated were determined. Soil solution concentration of these nutrients was also analyzed and used with the amount of transpired water to calculate mass flow. Diffusion was calculated by subtracting mass flow contribution from total nutrient plant accumulation. Potassium was transported predominantly by diffusion, except where K2CO3 was used, which yielded high soil solution K concentration and supplied enough potassium to the plants through mass flow. Calcium and magnesium were transported by mass flow. It is concluded that diffusion of potassium was the main mechanism of potassium transport but mass flow might solely supply plant demand when the concentration of potassium in the soil solution is very high.
cationic macronutrients; transport; Oryza sativa