Measurement of Grain Yield and Grain Protein Concentration In Autumn-Sown Winter Wheat as Affected by Nitrogen Source and Nitrogen Application Timing.

Improved nitrogen (N) management strategies are at the forefront of arable research worldwide as producers strive to improve agricultural sustainability and feed the ever increasing global population. In a field trial study in 2009, at two sites in Eastern Ireland, the effect of separated liquid pig manure (LPM) (3.5% N) and chemical fertiliser (CF) (27% N) application on winter wheat grain yield and grain protein concentration was assessed. Each trial had a 3 x 3 factorial design with three N treatments; LPM, CF and an untreated zero N control with N sources applied at three timings growth stage (G.S) 31 (1^st node), G.S 33 (3^rd node) and G.S 39 (flag leaf) with four replications. The LPM and CF treatments were surface applied at appropriate rates to supply 120 kg total N/ha. Lowest grain yield (5.58 t/ha) and grain protein levels (7.85%) were measured from the untreated zero N control. Chemical fertiliser application resulted in significantly higher grain yield levels than LPM usage (+9%) (9.02 vs. 8.24 t/ha).  However, LPM application resulted in significantly higher grain protein levels than CF (9.43 vs. 9.15%). Although grain yield levels were unaffected by N application timing, grain protein concentration significantly increased with N application at more advanced growth stages (range 8.67-8.93%). Grain yield levels were also affected by a N source x site interaction.  Chemical fertiliser outperformed LPM at site 1 (low N status soil), while at site 2 (high N status soil), CF and LPM behaved similarly. The results presented in this study support the hypothesis that separated liquid pig manure can be used successfully as the sole N source in winter wheat production. LPM usage represents a sustainable nutrient cycle in animal and crop production reducing farm inputs of chemical fertiliser, a product of fossil fuel based energy systems.