Pioneer® Seeds Products

The critical relationship between water availability and grain fill


It is extremely important to understand the importance of water availability in corn during the grain fill period. When corn crops are still in the dough stage of development, 50% of its yield potential is yet to be determined. Once corn reaches the dent stage, some so-called “experts” are often heard confidently stating that there is no reason to worry about further crop stresses because “the crop is made”.

Actually, by the time a crop reaches full dent (every kernel dented), only about 60% of the crop has been “made” and there is still 40% of the potential yield “on the table” yet to be determined.

Even by the time a crop has reached the so-called “half milkline” stage of kernel development (only about 10 to 14 days from physiological maturity), sudden and complete death of the whole plant can result in significant yield losses.


Recognise that a crop of corn is not “made” until it has successfully reached physiological maturity. That is the final stage of kernel development determined by the presence of the thin, black layer at the tips of the kernels that prevents further movement of photosynthate into the grain.

There is a common misconception that kernel black layer fails to develop in crops killed by drought, frost, or other severe stresses. This is simply not true. Kernel black layer will always develop in corn grain. In fact, kernel black layer will develop sooner than expected on a calendar basis in severely stressed crops.

When we talk about crops “shutting down” in response to severe stress, this means that the photosynthetic “machinery” is failing and the whole grain filling process is slowly coming to a grinding halt.

Prove this to yourself by inspecting ears from droughty areas of a field with those from well-watered areas and you will see that kernel black layer develops sooner in the droughty areas. The same holds true for other severe stresses, such as extreme nitrogen deficiency.

The effects of inadequate rainfall throughout much of the grain filling period, have at times been amplified by the effects of excessively warm temperatures.

Crops growing in soils with naturally low water-holding capacities or soils with significant levels of root-restricting soil compaction are the first to show the symptoms of drought stress (leaf rolling, lower leaf death, whole plant death).

However, even crops growing in “good dirt” can be affected by the persistent lack of timely or adequate rainfall, and or excessive heat.

It is imperative that growers recognise that such severe photosynthetic stress during the grain filling period can result in plants “cannibalising” themselves to meet the carbohydrate “demands” of the developing grain. 

This is especially true when pollination and initial kernel set have been good; resulting in ears with high kernel numbers. Stored carbohydrate reserves in the lower stalk and leaf tissues are often remobilised to the developing ears in response to photosynthetic stress.

Two consequences of such carbohydrate remobilisation are the:

1. Physical weakening of the lower stalk and
2. Increased susceptibility to root and stalk rots

Such cannibalised or diseased plants are naturally more apt to break over or lodge in response to strong winds, potentially turning grain harvest into a frustrating and challenging operation.

Source: Nielsen, RL (Bob). 2013. Grain Fill Stages in Corn.


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