Relationship among nitrogen and phosphorus contents of vegetative parts and agronomic traits of normal‐ and high‐protein wheats1

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Abstract
Nitrogen and phosphorus fertilizers were applied at different levels to three hard winter wheat cultivars ranging in grain protein potential to elucidate their interaction and relationship to yield components. Plant N content was higher in the high‐protein cultivar than in the normal‐protein cultivars at jointing two years and at anthesis one year. Plant P content was higher in the semidwarf cultivars than in the tall cultivar and was unrelated to protein potential. All cultivars contained similar plant N and P levels at maturity. Nitrogen fertilization increased plant N content and decreased plant P content at all stages, whereas P fertilization usually increased plant P content but did not affect plant N content. Grain protein was correlated positively with plant N content at all stages and with plant P content at maturity. Grain yield was correlated positively with plant N content at anthesis but correlated negatively with plant P content at maturity. We concluded that high plant N content at anthesis is necessary for high grain yield and protein content regardless of the cultivars1 inherent protein potential and that plant P nutrition is more critical when N nutrition is altered by fertilization or by genetics.