Describing and understanding barley growth and development through the use of benchmarks

Plots of winter barley, cv Pearl, were grown to a standard protocol at six sites across the UK, and in three seasons (2001to 2004). A detailed  programme of assessments was conducted to provide a quantitative understanding of the yield-forming process, to indicate where the yield-limiting steps exist in barley, and provide benchmarks for crop growth.

Benchmark dates for key growth stages (GS) were identified, with southern sites (Rosemaund, King's Lynn and Sutton Bonington) consistently reaching these key stages around 5 to 12 days before the northern sites (Edinburgh, Aberdeen and High Mowthorpe).  The leaf emergence rate (phyllochron), as with wheat, was linearly related to temperature, and on average taking 108 ºC days for each leaf to emerge.

High yields were associated with good overwinter growth and early spring N uptake.  Poor overwinter growth did not appear  due to low N availability but other factors, such as cool autumn temperatures,  slow germination and establishment.  Across all sites and seasons, average grain yield was 8.8t ha^-1 @ 85%DM.  On average, there were 775 ears m^-2, with 24 grains ear^-1, at a grain weight of 46 mg.  These and other benchmarks have been published in The Barley Growth Guide (HGCA, 2006). They provide a valuable reference point against which growers can assess the growth and development of their own crops. 

Yield appeared to be limited by the storage capacity of the grains (the number of grains produced and their potential size), rather than the ability of the crop to supply photosynthates for grain filling. Analysis of the yield forming process has shown that the number of grains m^-2 (ears m^-2 x grains ear^-1) accounted for 83% of the variation in yield between sites and years. 

High numbers of grains m^-2 were associated with high levels of pre-anthesis biomass accumulation and it is suggested that a target for future crop impovement is to extend the period between the start of stem elongation and flowering to increase grain numbers further.  A quantitative assessment of the amount of  photosynthates potentially available for grain filling has shown that they exceeded the storage capacity of the grain in 16 of the 17 site/years analysed, but that the scale of the excess differed greatly.

The results also show that the potential size of the grain is determined by both pre- and early post-flowering growth conditions. The amount of light intercepted by the crop per unit grain number during the period of early grain development appears to be particularly important in determining the final grain size (average grain weight). Crop management, therefore, may need to focus on protecting the canopy and ears during this critical early post-flowering phase.

Low grain N% was found to be associated with high average grain weights.  Thus, where low grain N% is required, it is important that agronomic treatments designed to increase yield by increasing the number of grains m^-2, do not lead to a corresponding decrease in average grain weight. Our results, based on the variation that occurred in crop growth between sites, suggest that there is scope for increasing grain numbers without significantly reducing average grain weight and increasing grain N%.