The three principal nutrient uptake pathways as reported by Barber (1995) are generally described as:
1. Root Interception – roots grow in a nutrient location
2. Mass Flow – nutrient moves with the soil water to the plant
3. Diffusion – nutrient movement is from higher to lower concentrations
The relative contribution for each nutrient uptake pathway for corn is shown in Table 1.
Table 1 Nutrient Uptake by Corn Roots__________________________
_________% of Nutrient Uptake by Method_______
Nutrient Root Interception Mass Flow Diffusion
Nitrogen 1 79 20
Phosphorus 3 5 93
Potassium 2 18 80
Most of the macronutrient nutrients move to the roots by either mass flow or diffusion. For P&K, most of the nutrients move to the roots by diffusion.
The data in Table 2 compares the time it takes for P&K to move 1 cm. in two different soils in Indiana (Silborbush & Barber, 1983).
Table 2 Travel Times for P & K Movement in a Soil__________________________
Time to Travel 1 cm. K Diffusion Rate, Expressed as a
P K Multiple of the P Diffusion Rate
times as fast as P
Raub Silt Loam 3.45 0.42 8.1
Chalmers Silt Loam 1.89 0.41 4.6______________