Relationship between wheat grain protein percentage and grain yield, plant growth, and nutrition at anthesis

Winter wheat (Triticum aestivum L.), var. Astral, was grown in 1983–1984 in 12 experimental fields located in the middle of the Duero Basin (Spain) and fertilized with several doses of N, P, and K. Among fields, the grain protein percentage increased with the ratio between above‐ground dry weight of the plant at anthesis and grain production (X4). This ratio accounted for 75.7% of the variance in grain protein percentage from one field to another. However, when the supply of some nutrient limited above‐ground nitrogen accumulation or translocation of nitrogen into grains, protein percentage in grain was better accounted for by the level of this nutrient multiplied by the above mentioned ratio. In addition, grain protein percentage showed the same pattern of variation with grain yield as X4. Within each field, grain protein percentage was, in general, mainly and positively correlated with the level of leaf nitrogen at anthesis. The regression lines varied among some of the fields, the intercept increasing with X4 and with the level of leaf magnesium. By contrast, the slope tended to decrease with grain yield.