Variability in soybean germ plasm for phosphorus uptake and use efficiency for dry matter yield

Twenty nine soybean [Glycine max (L.) Merr.] cultivars were evaluated and classified in relation to the response to P levels in the nutrient solution. P uptake and use efficiency, top and root dry matter yield, P concentrations and contents in plant parts and P efficiency index were estimated. The experiment was set up in a greenhouse, in 1999, in an Experiment Station of the Institute Agronomico, at Campinas, State of Sao Paulo, Brasil, and consisted of a randomized complete block design, arranged in a split-plot, with three replications. The main plots were the P levels in the nutrient solution (0.0645; 0.129; 0.258 and 0.516 mmol. L−1), and the subplots were the 29 soybean cultivars, grouped according to the cycle. The plants were harvested at flowering, separated into tops and roots and processed for dry matter determinations and chemical analysis of nutrients. Plant responses fit quadratic polynomial regression equations. Multivariate analysis showed high correlation among the variables: top and total dry matter (DM), P concentration in tops and P efficiency index (P-EI). Cultivars were classified in efficient-responsive (ER), efficient-non-responsive (ENR), inefficient-responsive (IR) and inefficient-nonresponsive (INR). The ER soybean cultivars showed the highest values for top and total DM and P-EI, and the lowest P-concentrations in the tops.