Grain number dominates grain weight in temperate cereal yield determination: Evidence based on 30 years of multi-location trials

Multi-location data collected over 30 years in Finland on major cereal crops (spring barley, oat and wheat, and winter wheat and rye) provide an opportunity to characterise variation, interrelation and relative importance of the grain yield determining components, grain number per square meter (GNO) and single grain weight (SGW). In addition to evaluating differences among cereal crops in yield determination, changes among different age groups (AG) were compared. Field experiments were carried out in 1970–2001 at 25 locations in Finland. Grain yield was recorded (at 15% moisture) and SGW (mg) and GNO (number m⁻²) determined. Frequencies of different GNO and SGW combinations were analysed for all crops and component means in different yield groups as well as among four AGs. In most cases GNO dominated SGW, representing the major yield component determining grain yield. GNO was highly responsive to favourable growth conditions. The change in GNO was especially high when recurrent, relatively low yield groups were compared, while at higher yields the role of SGW became increasingly important, but did not exceed that of GNO. The degree of GNO domination varied according to crop. Increased grain yield in spring oat and winter rye was associated with higher numbers of set grain, while spring barley and winter wheat responded to yield favouring conditions also through higher SGW. Despite GNO dominated SGW due to its responsiveness to growing conditions, its role in yield improvement was not obvious when the entries (n ≥ 30) were classified into four AGs. Improvements in grain yield derived from AG were associated with crop-specific GNO and/or SGW changes.