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Growth and Composition of Grain Sorghum with Limited Nitrogen

CIMMYT, Apdo. Postal 6-641, Col. Juarez, Deleg. Cuauhtemoc, Mexico 0660
Dep. of Agronomy and Range Sci., Univ. of California, Davis, CA 95616

^* Corresponding author.

A study of N fertilization of grain sorghum [Sorghum bicolor (L.) Moench] was conducted in two fields on a Typic Xerorthent with contrasting patterns of N availability, to extend our understanding of how the partitioning of N to vegetative parts and to structural biomass influences grain yield and N-use efficiency. The study was supported by detailed analyses of N and dry matter distribution, and proximal analyses of biochemical composition. Nitrogen accumulation differed greatly, but the patterns of N partitioning and the structural carbohydrate content of vegetative parts at equivalent developmental stages were little affected. Changes in dry weight partitioning among vegetative parts were primarily a result of the parts' differential abilities to store nonstructural compounds. In contrast, the structural carbohydrate content of panicles was affected by N availability. Low N supply resulted in leaves with a smaller N content, and lower light conversion efficiency was observed. In addition, those canopies were not able to supply as much N to panicle growth. Roughly two-thirds of the observed effects of N deficiency on grain yield were due to structural limitations to growth; the remaining effects were associated with reduced conversion efficiency per unit leaf area.

Key Words: Sorghum bicolor (L.) Moench • Nitrogen utilization efficiency • Nitrogen mobilization • Light utilization efficiency

Received for publication February 23, 1987.