The management of some crops focuses on measuring overall leaf index per plant as an indicator of the fruit load the plant can support.
But this doesn’t seem correct. Leaves on new growth shoots and leaves associated with fruit do not contribute sugar to the fruit sinks equally.
In many crops, the majority of the sugars that are stored in the fruit or seed come directly from leaves that fruit is most closely associated with. These might be spur leaves, bract leaves or nodal leaves on different types of crops.
My present understanding is that as little as 35% to as much as 80+% of the sugars in the fruit or grain (or cotton fiber) is sourced from these closely associated leaves.
This means we need to pay closer attention to individual leaf size, rather than overall plant size and leaf index. The surface area and photosynthetic capacity of the leaves closely associated with fruit or seed will have the greatest impact on fruit size and quality.
This also offers an explanation why some of the highest yielding crops I have observed did not have a great deal of vegetative biomass. They were reproductive energy dominant and had limited vegetation, but individual leaves were very large in size, which resulted in an abundant sugar source for the fruit sink.
The practical application of this idea is that we have to make sure zinc (and other foundational nutrients) levels are in generous supply for those fruit associated leaves to produce supersized individual leaves before or during leaf bud development.
