Effect of Pot Size on the Growth of Common Bean in Experiments with Rhizobium

Abstract

The initial steps for the selection of microbial inoculants are carried out in pots. The sizes of the pots must be taken into account, since plants respond to different pot sizes. The objective of this study was to verify the effect of pot size on the outcomes of the evaluation of rhizobial inoculants in common beans (Phaseolus vulgaris L.). Two experiments combining three pot sizes (1, 3, and 5 kg of soil) and three N sources (rhizobia, mineral N, and the absence of inoculation and N fertilization) were carried out. In experiment I, the pots received fertilization according to soil mass. In experiment II, the pots received equal amounts of fertilizer. Plants were harvested at the R6/R7 stages and their biomass and nodulation were assessed. Plant growth increased with pot size in both experiments. Although 1-kg pots did not provide phytomass accumulation in the same magnitude as larger pots, they allowed differentiating responses to inoculation and nitrogen fertilization. Thus, when required, 1-kg pots can be used for strain selection assays. When receiving the same amount of nutrients, the pots of 3 kg of soil provided plant development similar to 5-kg pots, showing that soil fertility was more critical than pot size in determining plant growth. Our study revealed that among the evaluated sizes, 3-kg soil pots are best suited for detailed plant growth evaluations in rhizobia experiments. This size adequately differentiates treatments, reduces experimental effort, and may allow a greater number of treatments under evaluation.