Developing grains were harvested from wheat plants grown in pots which had received additional late P‐fertilizer applications. By sequential extraction of milled grain samples of different developmental stages total P (Ptot) and the P‐fractions lipid‐P (Plip), phytin‐P (Pphy), inorganic and soluble ester‐P (Pi+e) and residual‐P (Pres) were determined.‐Due to the late P‐application, grain yield, Ptot, and Pphy content of ripe grains were increased by 14%, 58%, and 80% respectively, compared to the control. 93 % of the P which accumulated additionally in the grains as a result of the late P‐application, were found to be Pphy.‐During grain development the amounts of Ptot and Pphy per 1000 kernels increased steeply whereas those of Plip and Pres were not significantly affected by the stage of grain development or by the rate of P‐application. Pi+e increased during the first stages of grain development but subsequently decreased towards nearly the same low level regardless of the treatment.‐The increased phytin concentration in the ripe grains resulted in a decreased zinc bioavailability as was indicated by feeding experiments with growing male rats.

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