Yield structure and pre-anthesis carbohydrate status of wheat

Abstract

In the 1977-78 and 1978-79 seasons, three field experiments were conducted on a deep moisture retentive soil to investigate the responses of wheat yield to various seeding rates, rates and times of N application, and irrigation during grain-filling. Increasing seeding rate from 250 (normal) to 500 seeds/m² increased spike population which was associated with low concentration of Total Nonstructural Carbohydrates (TNC) within the plants during the time of pre-anthesis and accompanied by a reduction in the number of grains per spike, but it did not affect the weight per grain and the grain N concentration. Thus higher than normal seeding rate did not significantly affect grain and N yield. Application of N equally divided between tillering and the spikelet development stage increased grain yield in the first season mainly because its positive effect on spike population. However, in the second season grain yield was decreased in response to early N application because of a reduced grain set and grain weight but late applied N did not influence yield. The seasonal variations in responses of grain yield to N application were apparently related to differences in the levels of TNC within the plants during reproductive development. Grain N concentration was increased with applied N but the relationships between grain yield and grain N concentration varied depending on changes in plant growth. Irrigation during grain-filling tended to improve grain weight and to remove the negative correlation between grain yield and grain N concentration. The results are discussed in relation to the importance of the status of TNC within the plants during the ten weeks before anthesis and wheat development and yield.