Impact of Management Practices on Grain Yield and Grain Protein Relationships in Durum Wheat

We examined the relationship between grain yield (GY) and grain protein concentration (GPC) in durum wheat ( Trticum turgidum L. var. durum ) as affected by N application rate, seeding rate, and irrigation levels. Field experiments were conducted for four years with five N rates, five seeding rates, and four Irrigation regimes: A. Only a preplant irrigation; B. A + one irrigation at tillering; C. B + one irrigation at booting stage; and D. C + one irrigation at early soft dough stage. These treatments produced a large variation in GY and GPC which provided the basis for examining the GY-GPC relationship by all possible correlation analyses and by analysis of variance after partitioning the bivariate responses (GY and GPC) into pairs of univariate responses. The contribution of N, seeding rate, and irrigation on parallel (simultaneous changes in the same direction) and opposite changes in GY and GPC was determined. The effects of N and seeding rate on parallel increase in GY and GPC were significant. For a given level of irrigation, increasing N application resulted in significant parallel increase in GY and GPC to the highest level of N. At low N levels, increase in irrigation level from A to B increased GY and decreased GPC; however, it was not true at higher N levels. For a given N level, GY plateaued at irrigation C, whereas GPC increased up to irrigation D. The overall effects of irrigation treatments on parallel changes (positive correlation) in GY and GPC significantly outweighed their effects on opposite changes (negative correlation) in GY and GPC. Increasing levels of N and irrigation improved the correlation between GY and GPC and the yield-protein index. This study suggests that with proper management practice it is possible to increase both GY and GPC simultaneously and obtain high protein yield ha⁻¹.