PHOSPHORUS EFFECTS ON ROOT-GROWTH AND DEVELOPMENT IN 2 MAIZE GENOTYPES

Soil phosphorus (P) availability is critical for the early growth and development of maize (Zea mays L.). Soil P also affects root morpholog ical and physiological characteristics that are important for P uptake . The objective of this study was to evaluate the effects of P on seed ling root growth and development of two maize genotypes differing in r oot system plasticity. Two maize genotypes, CM37 (high plasticity) and W153R (low plasticity), were selected based on a preliminary study. M aize plants were evaluated at six vegetative stages of development for three soil P treatments (0, 45, and 300 mg kg(-1)). Seedlings were gr own in a controlled environment using a soil with low native P, Maddoc k sandy loam (sandy, mixed Udorthentic Haploborolls), The addition of P decreased the time to reach a given growth stage and increased the r elative growth rate of roots to a greater degree in CM37 than in W153R . The effects of P on shoot dry weight and root surface area during th e V4-V6 growth period appeared to be related to the effects of P on de velopment and relative growth rates during the V1-V3 growth period. Ev aluation of the time course of phenotypic change is an important consi deration when developing adapted genotypes for specific environments.