Root penetration of the soil is the result of:
- Plant characteristics (e.g., grass
roots less deeply than white cabbage).
- Soil properties (pore size distribution,
surface crusting, soil compaction affect gas exchange
and/or soil mechanical resistance, and consequently the root's ability to penetrate to greater
depths).
Weather conditions (soil water content as a result of precipitation and/or soil temperatures
influence root growth).
For nutrient uptake and availability, the following are significant:
- Rooting depth (depth of root penetration):
This determines the maximum total soil volume that
can potentially be exploited. This is why, for the Nmin soil test, samples are taken to different
depths for different crops.
- Root length density (degree of root
penetration in a given soil volume): This determines to what
extent a given soil volume can be depleted of nutrients. For mobile nutrients, a few cm of root
per cubic centimeter of soil are sufficient for complete depletion, while for immobile nutrients,
complete depletion is hardly possible.
- Root activity (root age, oxygen demand,
etc.) in the soil layer.
From these few factors alone, a multitude of possible scenarios promoting or hindering
nutrient
transformation processes and nutrient uptake can be derived. In my opinion, a quantitative
understanding of these interactions can only be achieved by:
- Quantifying the individual processes,
- Combining the various processes according
to their interdependencies, and
- Utilizing mathematical modeling to
estimate the effects.
