Modelling N and Dry Matter Partitioning between Leaf and Stem of Wheat under Varying N Supply

• Published in: Journal of agronomy and crop science (1986) 2016-12, Vol.202 (6), p.576-586
• Main Authors: Ratjen, A. M., Kage, H.
• Format: Article
• Language: English
• Subjects: crop/stress physiology; mineral deficiency stress; modelling; nitrogen deficiency; Triticum aestivum
• ISSN: 0931-2250; 1439-037X
• DOI: 10.1111/jac.12180

The fraction of dry matter and nitrogen (N) allocated to leaves is of high importance for wheat crop simulators, because it has an impact on N demand, evapotranspiration, light interception and light use efficiency. For the vegetative phase of wheat, a robust empiric description of the influence of N nutrition status (NNI) on this pattern is still pending. We investigated the influence of NNI on leaf: stem partitioning of wheat (Triticum aestivum L.), until end of leaf growth. The evaluation based on N rate experiments (0–320 kg N ha−1) from three subsequent seasons (2003/4 to 2005/6), with five modern bread wheat cultivars, carried out near Kiel (northern Germany). A previously published model was adapted for describing the influence of NNI on dry matter partitioning. Starting from the allometric leaf: stem relationship of situations with NNI ≥1, a correction term was used, to describe the partitioning under varying N supply. The correction term assumes a linear increase of the stem fraction, proportional to the difference between a NNI threshold and actual NNI. The allometric partitioning was found to shift towards stem fraction, if the NNI falls below 1.38. The slope of the relative increase was determined with 0.6. Both dimensionless parameters of the correction term were found to be highly significant. The second aim was to quantify how N status impacts the N allocation between shoot organs. Dry matter‐based N dilution curves were fitted for stem (plateau power) and leaf (plateau linear), for situations with sufficient N supply (NNI ≥1). The ‘expected’ shoot N demand was calculated as a function of observed dry matter and N dilution for both organs. The N deficit was defined as difference between expected and observed shoot N. Plotting stem against shoot N deficit reveals that 63 % of the shoot deficit was allocated to the stem (R2 = 0.98). Implications for crop modelling are discussed.