The Range of the Critical Nitrogen Dilution Curve for Maize (Zea mays L.) Can Be Extended Until Silage Maturity

The concept of critical N concentration (Ncrit) assumes at any time a minimum shoot N concentration necessary for maximum biomass production. For maize ( Zea mays L.), Ncrit has of now been confirmed only from emergence to silking plus 25 d. These results were based on mineral N fertilization. In the present study, we verified that the validity of the concept can be extended to silage maturity and that it is not only applicable to mineral but also to organic N fertilizer. Our investigation included a 3‐yr N fertilization experiment comprising four mineral N fertilization rates (0, 50, 100, and 150 kg N ha −1 ) and three slurry treatments (0, 20, and 40 m 3 ha −1 ), respectively. A quadratic‐plateau model was used to determine Ncrit values. An analysis of covariance indicated that the Ncrit‐to‐biomass relationship was extendible to the postsilking stages. The Ncrit [g N kg −1 dry matter (DM)] was then successfully described by a mononomial function of biomass W (t DM ha −1 ): Ncrit = 34.12· W −0.391 We suggest restricting the model to growth stages with biomass exceeding a threshold of 1 t ha −1 Model validation against an independent data set comprising different hybrids and soil conditions indicated a satisfactory separation of N‐limiting and non‐N‐limiting growth. The Ncrit concept thus seems to provide an efficient tool for assessing the N status of forage maize for mineral and organic N fertilizers and for a broad range of hybrids, climates, and soil conditions.