The precise definition of rooting depth is difficult. Root development and nutrient uptake is also affected by the supply of water. Root proliferation at depth occurs when the upper zone dries out. The latter depends on the supply of osmotica and on water uptake. Nutrient uptake is affected by soil water content through mass flow and ion diffusion.
Diffusion coefficients increase almost linearly with water content.
Suitable water content gives reduced leaching, and less variable N-levels in the soil. Burns, I. G . Workshop Ecological Aspects Veg. 428, ISHS 1996. Rahn, C.R .