Developing a nitrogen fertilizer management model for wheat in calcareous soils using the critical nitrogen dilution curve
Ali M. Ali, Ahmed M. Saudi, Ashraf El‐Sadek, Bijay Sıngh
Abstract
Abstract The critical nitrogen (N) dilution curve, which expresses whole-plant critical N concentration as a function of shoot biomass, can be used as a N management diagnostic tool for cereals. The objectives of this research were to develop a critical N dilution curve for wheat grown in calcareous soils and to formulate a model for estimating N fertilizer requirement of wheat crop at different growth stages. Six N fertilization rates (0–250 kg N ha −1 ) were used to induce variability in plant growth throughout six site-years (three locations at West Delta of Egypt and two seasons [2020/21-2021/22]). Aboveground shoot biomass ( W ; Mg DM [dry matter] ha −1 ) and N concentration ( N c ; g kg −1 DM) were determined on five sampling dates during the growing season. A critical N dilution curve was developed as: $${N}_{\mathrm{c}}=50.141 {\mathrm{W}}^{-0.424}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>N</mml:mi><mml:mi>c</mml:mi></mml:msub><mml:mo>=</mml:mo><mml:mn>50.141</mml:mn><mml:msup><mml:mrow><mml:mi>W</mml:mi></mml:mrow><mml:mrow><mml:mo>-</mml:mo><mml:mn>0.424</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math> . The N c dilution curve was then used to develop a N fertilizer topdressing strategy. The study relied on N nutrition index inferred from the N c based on N uptake, and instead of relying on a single N recovery efficiency coefficient, a variable N recovery efficiency was developed. This approach increased the hypothetical N requirements at low N application rates while decreased requirements at high N application rates, implying that the N c dilution curve can be used successfully to estimate the rates of supplemental N application. The developed strategy will provide a solid basis for precisely managing N fertilizer, though challenge ahead at the farm level will be in determining the actual shoot biomass and N concentration.