These tomato plants are watered 30 minutes twice a day to maintain a constant water supply as measured by an irrometer. As nutrients are absorbed by the plant roots, they follow the upward flow of water to the leaves and fruit.
Aside from photosynthesis, the water is used in two very different metabolic processes; respiration (metabolism) and transpiration (cooling).
Older mature leaves and new developing leaves transpire at almost equal rates.
Newer leaves respire much more than older leaves since they are still developing and actively growing.
For this reason, the greatest flow of water is directed to the new growth. As long as the new growth is actively growing.
This also means the majority of nutrient flow is directed to the new growth.
Whenever the water supply is inconsistent or in adequate, respiration is greatly reduced, while transpiration continues in both mature and young leaves.
(Newer leaves have the greatest water requirement since they are both transpiring and respiring, they are the first to wilt.)
In an environment with restricted water, nutrients flow almost equally to both young and old leaves, following the transpiration stream.
When the plant is provided with adequate water and begins to recover, the mobile elements will move out of the older leaves and up to the new growth.
Less mobile elements such as calcium, and to a lesser extent magnesium, will remain in the older leaves and accumulate over the course of the growing season as in the example.
The nutrients which have accumulated in the older leaves are not metabolically active, and usually produce deficiencies of the same elements in the new growth.
“Providing a consistent high quality water supply is a shortcut to success.”
A consistent water supply is critical to enable proper nutrient flow in plant sap and ensure plant health and fruit quality.