Development of a critical nitrogen dilution curve of Siberian wildrye for seed production

The critical nitrogen dilution curve (CNDC) is usually used as an efficient method to diagnose nitrogen (N) status of crop plants. However, there is no successfully developed CNDC for forage species seed production. The objectives of this study were to develop an appropriate CNDC in seed production and to manage nitrogen application accurately in seed fields of Siberian wildrye (Elymus sibiricus L.). Two experiments were carried out with N application treatments (0-225 kg N ha−1) in two successive growing seasons (2014 and 2015) at Yuershan Farm in Hebei Province, China. Shoot biomass (t ha−1), nitrogen concentration (percentage of dry matter), and seed yield (kg ha−1) were measured to calculate critical N concentration, development and validation of the CDNC. The CNDC for Siberian wildrye seed production was developed with the equation Nc = 3.00 W−0.32 (determination coefficient 0.97), based on shoot biomass (between 0.9 and 7.1 t ha−1) and its N concentration. According to the independent data set grouped by seed yield, the developed CNDC could adequately identify the situations of N-limiting seed yield and N non-limiting seed yield before and during anthesis stage, the optimum seed yield was reached at around NNI = 1. The CNDC developed in this study provides insight to improve N diagnosis and management in Siberian wildrye seed production under rain-fed conditions.