Effect of timing of defoliation on wheat (Triticum aestivum) in central Queensland

Aspects of nitrogen uptake and use efficiencies were studied in trials quantifying the impact of artificial defoliation on wheat yield and protein content. Late defoliation (after ca. 50 days after sowing, especially in later sowings) led to an increase of hay production, a reduction of N as grain, and nearly always an increase in total N removal. The optimum range of N removal in hay by defoliation was 8-12 kg ha−1 leading to a maximum grain N of 75-79 kg ha−1 and a significantly greater total N recovery and use efficiency. This may be due to greater uptake per se, to reduced plant volatilization of N, or to a combination of the two. The ecological consequence of capturing more N in hay before it is possibly volatilized from plants later in the season is an added benefit to defoliation.