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Shading Effects on Dry Matter and Nitrogen Partitioning, Kernel Number, and Yield of Maize

Monsanto Agric. Co., 700 Chesterfield Village Parkway, Chesterfield, MO 63198
Dep. of Agronomy, Univ. of Illinois, Urbana, IL 61801
USDA-ARS, North Central Soil Conservation Res. Lab., Morris, MN 56267
ARS-NPS, BARC-West, Beltsville, MD 20795

^* Corresponding author.

Assimilate supply to the developing ear of maize (Zea mays L.) is an important determinant of grain yield. The objective of the current study was to determine the relative limitations of photosynthate and reduced N supply to the ear for determination of yield components, kernel number and kernel weight. Field-grown maize plants on Dupo silt loam (Coarse-silty over clayey, mixed, nonacid, mesic Aquic Udifluvents) were shaded during either vegetative growth, flowering, or grain fill. Control plants were not shaded. Photosynthesis was measured on plots from 9 d before flowering to grain maturity, and plants were sampled at intervals during this period for measurement of dry weight and reduced N content of plant parts of the aboveground vegetation (stover) and ear. When plants were shade during flowering, photosynthesis decreased during this period and kernel abortion increased relative to controls. However, N concentration was higher in aborting kernels than in nonaborting kernels through late flowering and early grain fill. The supply of reduced N to the ear during flowering was not a limiting factor for determination of kernel number. During grain fill, remobilization of N and dry matter from the stover of controls accounted for 46.5 and 4.7% of ear N and dry weight at maturity, respectively. Availability of newly reduced N was apparently more limiting than availability of current photosynthate for kernel dry weight accumulation. It is proposed that supply of newly reduced N to the ear may be limited by the amount of photosynthate partitioned for nitrate uptake and reduction during grain fill.

Received for publication September 25, 1987.

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