In a maximum yield experiment in Ontario, Canada, response of maize (Zea mays L.) to greater than recommended P fertilizer applications seemed to result mainly from improved P nutrition of seedlings. A 2‐yr study was conducted to determine the effect of P nutrition during the seedling stage on final yield. An outdoor, hydroponic system was used to vary P nutrition during growth and provide adequate levels of all other nutrients and water. Plants receiving the greatest or an intermediate P concentration solution had P concentrations of 7.2 and 4.4 g kg−1, respectively, at the 6‐leaf stage, whereas plants receiving the least P concentration solution had a shoot P concentration of 2.8 g kg−1. Plants that received the intermediate or least P solutions until the 6‐leaf stage but then received the greatest P solution to maturity attained shoot P concentrations of at least 5.0 g kg−1 8 d after increasing the P solution concentration. Grain yield was greater on treatments receiving the greatest P solution from the beginning than from the 6‐leaf stage (8.2 vs. 7.2 t ha−1), mainly because of a greater kernel number. Kernel number was most sensitive to P nutrition during the period from planting to the 6‐leaf stage. A shoot P concentration of at least 5.0 g kg−1 at the 6‐leaf stage was required to obtain maximum yield.
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Barry et al. (1989) studied this question.