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

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Abstract
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). The fields were fertilized at several rates of N, P, and K. Grain protein yield increased linearly with grain yield and with above‐ground plant dry weight at anthesis. Above ground dry weight of the crop accounted for 91.1% of the variance in grain protein yield among the different fields. The grain protein yield also increased linearly with leaf nitrogen level at anthesis. However, within each field, grain protein yield was generally more closely related with above‐ground dry weight at anthesis multiplied by the level of nitrogen in the two uppermost leaves (X3), than with any of these factors considered separately. The regressions over X3 were positive and varied among some of the fields. The intercept increased with grain yields and the slope with the concentration of magnesium. In addition, the ratio between grain protein yield and X3 increased with the leaf magnesium level. This suggests that grain might favour the assimilation of exogenous nitrogen during its development and/or the translocation of nitrogen from the vegetative parts of the plant to the grain. Moreover, magnesium might increase the efficiency of protein accumulation in grain. Among fields, the relationship of grain protein yield with leaf magnesium level depended on the level of nitrogen.