A literature survey was conducted to determine the variability of tissue N and P concentrations
in maize (Zea mays L.) and grain sorghum (Sorghum bicolor (L.) Moench)
shoots, roots, grain, and residues. Tissue N and P concentrations associated with near optimum
yields, the ratio of shoot N to shoot P, the relationship between harvest indexes
for N and dry matter, and the relationship between shoot N concentration and grain N
concentration were also investigated. For maize at near-optimum yield levels, growth
stage has been shown to account for 86% of the variation in shoot N concentration prior
to growth stage 8 and 82% of the variation in shoot P concentration prior to growth stage
4. The range of grain sorghum shoot N concentrations was similar to that of maize, but
data were inadequate to estimate the range or optimum of grain sorghum P concentrations.
The ratio of maize shoot N to shoot P concentration was variable; however, at near optimum
yield levels, the ratio was quite predictable. Maize and grain sorghum root N
concentrations were less variable than shoot N concentrations and were not strongly
dependent on growth stage. Grain and residue N and P concentrations were variable, but
over 70% of the variation in maize grain N concentration was accounted for by shoot N
concentration.