Barley and its environment. 6. Growth and development in relation to yield.
Detailed measurements of the growth and development of a crop of barley cv. Proctor were used to study the processes determining ear number/unit field area (Ne), grain number/ear (Ng) and mean weight/grain (Wg). Many more tillers were produced than eventually bore ears; their death may be due to shortage of assimilate after the crop surface was effectively closed (LAI >3). Spikelets were initiated on the apex at a nearly constant rate from 31 to 63 days after sowing, giving a maximum number of approximately 35. In the following 30 days, about 50% of these died leaving an average of 18 grains/ear. Spikelet death may be due to the unfavourable position of the ear for assimilate supply and competition for nutrient within the developing ear itself. Wg increased at a nearly constant rate for about 25 days. Approximately 90% of the increase in grain weight occurred during this linear phase. Differences in mean weight/grain at harvest can be resolved into differences in either the rate or the duration of grain growth. Quantitative expressions were derived allowing the processes determining Ne Ng and Wg to be described by a few simple variables. The usefulness of these variables for investigating the effect of environment on yield components was tested by reference to published measurements. The analysis emphasizes the importance of making concurrent measurements of crop DM production, photosynthetic area and the processes of tillering and ear development when studying the effects of environmental factors on cereal yield.