Abstracts Biological Sciences

Grain yield and quality of malting barley (Hordeum vulgare L.) as influenced by nitrogen

by A. G. Fergusson

An experiment was run from September 1997 to February 1998 using "Valetta" barley at Lincoln, Canterbury, New Zealand. Grain yield and grain quality were measured in response to different rates and timings of nitrogen (N) fertiliser. Biomass accumulation, leaf response and biomass and nitrogen distributions during grain filling were also measured. The highest grain yield of 7030 kg ha????? at 0% moisture (8000 kg ha????? at 14% moisture) with a grain N% of 1.64 was obtained with a single application of 150 kg N ha????? at crop emergence 21 days after sowing (DAS). Grain yields and grain N % decreased with lower N rates while screenings and grain N% increased with additional applicati.ons. Harvest index averaged a mean of 47%, but varied between 44 (nil N fertiliser) up to 57% (150 kg N fertiliser). Total biomass was greatest (16020 kg ha?????) in the highest N fertiliser treatment of 150 kg N ha????? at crop emergence with an additional application of 100 kg N ha????? at Zadoks growth stage 18. This treatment produced a peak growth rate of 310 kg biomass ha????? d????? at 87 DAS and a mean growth rate over the linear phase of growth of 205 kg ha????? d?????. All other N treatments had lower growth rates. The linear phase of crop growth was the same for each treatment at around 75 days. Radiation use efficiency was about the same for all treatments at a mean of 2.00 g biomass per MJ photosynthetically active radiation (PAR) intercepted. The differences in total biomass produced were related to the amount of PAR intercepted, 524 MJ m????? in the highest N fertiliser treatment from 61 to 110 days after sowing, compared with 445 MJ m????? where no N fertiliser was applied. Maximum leaf area index (LAI) was the main contributor to the amount of PAR intercepted, being highest at 3.8 in the high N treatment. Leaf lamina responses to applied N fertiliser showed that leaves maintained a specific leaf nitrogen level at about 2.0 g N m????? leaf?????. To maintain this level, leaves with lower N availability decreased the green area of the lamina when fully emerged. Specific leaf weight (weight per unit green leaf area) was not affected by N fertiliser treatments in any treatments. Biomass and nitrogen relocated during grain filling was affected by the amount of N available at anthesis and the growth rate at anthesis. In general, the formation of a total plant N pool at anthesis of 2.0% or less gave acceptable grain quality, and yields greater than 7000 kg ha????? could be expected. The grain yields and quality were more affected by the N pool than the biomass relocation. Excessive plant N (>2.0%) from split applications of N fertiliser increased plant growth, rather than reserve assimilate production for grain. This decreased the amount of biomass accumulated in the grain as shown by increased levels of screenings. It was concluded that at this site, to obtain high yields and acceptable grain quality with the use of N fertiliser in an adequately water supplied malting barley crop, 150 kg ha????? of N fertiliser…