Physiology and Management to Increase Crop Nitrogen Accumulation and Grain Yield.

The history of yield increase is closely aligned with providing more nitrogen to crops.  Yield is quantitatively linked to the amount nitrogen that is taken up by the crop and eventually deposited in growing seeds.  Since much of the nitrogen accumulated by the crop must be done during vegetative development when photosynthate is available to support uptake, storage of nitrogen in the vegetative plant has become a key bottleneck in increasing nitrogen accumulation and yield.  The uptake processes are tightly regulated by feedback to limit nitrogen uptake to the capacity of the plant to store the nitrogen.  Therefore, physiological improvement will require increased plant storage capacity, likely by increased amounts of storage proteins in stems.  If the seed fill period can be extended, slowed seed growth paired with some sustained nitrogen uptake during seed growth could potentially increase yields.  There are several consideration in crop management to increase nitrogen uptake and storage.  Vigorous early season growth and high plant densities will result in increased vegetative storage capacity for crop nitrogen storage.  It is important to have nitrogen available in the soil when the crop has the capacity for high uptake rates.  Key considerations are the timing of nitrogen fertilizer applications and achieving maximum nitrogen return from crop residue from the previous crop.  Finally, future management schemes will likely be needed to enhance the role of legumes to provide an economic and effective source of nitrogen to the over all cropping system.