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Yield Predictive Worth of Pre-Flowering and Post-Flowering Indicators of Nitrogen Economy in High Yielding Winter Wheat
Indicators of nitrogen economy in winter wheat during vegetative development are a reliable tool for yield prognosis. This hypothesis was verified in a field experiment, carried out in the 2013/2014, 2014/2015, and 2015/2016 seasons. The field experiment, in a two-factor split-plot design, included the following systems of wheat protection (CFP): (i) N + micronutrients, (ii) N + fungicides, (iii) N + micronutrients + fungicides; and N rates: 0, 40, 80, 120, 160, 200, 240 kg N ha−1. The content and accumulation of N in wheat at the beginning of stem elongation and at heading were used for grain density and yield prediction. In the grain-filling phase, the stem N acted as a buffer, stabilizing yield at a high level. The condition for such action was the stem N equilibrium with the ear N at flowering. The N depletion from the leaves during the grain-filling period significantly depended on the grain density. The post-flowering uptake of N by wheat was affected by the grain density, which was affected by the N reserves in the stem. Yield forecast based on pre-flowering indices of nitrogen economy in cereals affects both agronomic decisions aimed at correcting the nutritional status of plants, and farm economics.
A Realistic Approach to Calculating the Nitrogen Use Efficiency Index in Cereals with Winter Wheat (Triticum aestivum L.) as an Example
Nitrogen use efficiency (NUE) is a reliable index of nitrogen (N) management, given that it expresses the real relationships that exist between crop yield, its components, and the content of available N (Nmin) in the soil in the critical stages of yield formation. This article proposes a method for calculating NUE which is based on N input (Nin) into the soil/crop system in the critical phases of yield formation in winter wheat. For the validation of this hypothesis, a field experiment with WW in three subsequent growing seasons (2012/2013, 2013/2014, 2014/2015) was used. Treatments were arranged in a factorial distribution of two factors: (1) three rates of soil-applied magnesium (Mgs, 0, 25, 50 kg Mg ha−1); (2) foliar application of Mg to winter wheat (no application—control; double-stage Mg application in BBCH 30 and in 49/50). The dose of N fertilizer (Nf) was 190 kg ha−1. Two groups of N pools (soil Nmin and N mass in the wheat biomass) were determined in BBCH 30, 58, and 89. These core datasets were used to calculate total N input (Nin) to the soil/crop system during the two main periods of WW growth: (1) before (vegetative mega-phase, V) and (2) after wheat flowering (reproductive mega-phase, R, or grain filling period, GFP). The number of grains per ear (GE) and the number of grains per unit area (grain density: GD) depended significantly on Nin at the onset of flowering. A Nin58 of 517 kg N ha−1 resulted in a GD of 28.3 × 1000 grains m−2, producing 9.47 t grain ha−1. The NUE indices calculated in the V phase were the best predictors of GE and GY. The apparently low NUE index in this phase clearly indicates (i) the high potential of winter wheat for grain set per ear, (ii) consequently resulting in a strong depletion of N soil resources during the GFP. Therefore, the reduced NUE before winter wheat flowering is essential for the achievement of a high GD. The NUE feedback phenomenon as found in this study is a crucial condition for the effective depletion of the inorganic N pool during the grain filling period of winter wheat. It can be concluded that the NUE indices obtained in the V mega-phase actually describe the N economy in winter wheat production very well.
Inorganic Fungicides (Phosphites) Instead of Organic Fungicides in Winter Wheat—Consequences for Nitrogen Fertilizer Productivity
Substitution of organic with inorganic fungicides (phosphites, Phi) does not change the efficiency of fertilizer nitrogen (Nf) in winter wheat. This hypothesis was tested in the 2016/2017 and 2017/2018 growing seasons. A two-factorial experiment with three phosphite variants (Cu–Phi, Mg–Phi, and Cu/Mg) and six plant protection methods (fungicides + Phi ⟶ reduced fungicide frequency + phosphite ⟶ phosphite). Grain yield decreased with increasing frequency of phosphites instead of fungicides. The decrease in yields was 3.6 t ha−1 in the favorable 2016/2017 and 1.1 t ha−1 in the dry 2017/2018. The primary reason for yield decrease in a given growing season was increased wheat infestation by pathogens. The direct cause was disturbances in the nitrogen status of wheat after flowering on treatments with a predominance of phosphites. The thousand grain weight (TGW) responded negatively to reduced fungicide application frequency. The critical stage in the assessment of pathogen pressure on wheat was the medium milk phase (BBCH 75). At this stage, indices of SPAD and leaf greenness together with indices of wheat infestation with pathogens allowed for a reliable prediction of both TGW and grain yield. It can be concluded that phosphites do not substitute organic fungicides in limiting pathogen pressure in winter wheat. Moreover, increased pressure of pathogens significantly reduces Nf productivity.