Approximately 80% of the world's agriculture is rainfed. Based on projections for future precipitation patterns, we may expect adverse impacts, such as yield penalties, on crop production due to a variation on the rainfall distribution (Bates et al., 2008). Based on that scenario, current plant breeding programs are taking into consideration the agriculture expansion over the globe, and including regions where rainfall and soil nutrients may be a limitation (Lynch, 2007). One of the plant characteristics that have the potential to improve crop adaptability to different environments is the root system. Soybean [Glycine max (L.) Merr.] cultivars, for example, differ on the response to flood irrigation, where the root system can play an important role to adapt varieties to adverse conditions like dry regions or poor drainage soils (Heatherly and Pringle, 1991). Investing in the root system (i.e. root length, surface area, average root diameter, and total root volume) can be a strategy for the plant to support adverse conditions like drought and poor soil fertility in the future (Hansel et al., 2017). Thus, investing in root growth can also be beneficial to enhance nutrient uptake in environments with low soil test levels for nutrients.

Root growth is particularly important for the uptake of immobile nutrients such as P and K (Lynch, 2007). The capacity to develop a deep root system early in the season can help plants to increase nutrient uptake. Roots must reach the soil volume where the nutrient is located, and the nutrient must be able to move into the root (Ober and Parry, 2011). Studies showed a direct relation between root biomass and P and K uptake in wheat (Triticum aestivum L.) (Ehdaie et al., 2010) and soybean (Hansel et al., 2017). Nutrient acquisition is also highly dependent on characteristics that can be identified as the root architecture of the plant (Gregory, 2011). Researchers have developed soybean genotypes with enhanced root traits for better adaptation to soils with low soil P levels (Yan et al., 2006). However, studies evaluating genotypic variation in root systems of soybean are currently very limited. For corn (Zea mays L.), results from previous studies showed significant differences in aboveground plant nutrient uptake among corn genotypes with different genetic backgrounds (Gordon et al., 1998). This suggests that possible differences in root systems among corn genotypes can contribute to differences in nutrient uptake from the soil and fertilizer application. However, nutrient concentration in the root and changes with the increase in root biomass has not been evaluated.

Characterizing root morphological properties such as total length, root system surface area, average root diameter, and branching patterns can be assessed accurately using new root analysis software based on image analysis. According to Bouma et al. (2000) and Himmelbauer et al. (2004), root length and root‐diameter distribution measurements provided by the WinRHIZO software (Regent Instruments) are accurate when the correct scanning protocol is followed. Therefore, computer‐assisted root imaging is an opportunity to facilitate the analysis process and improve accuracy.

Our study hypothesizes that different corn and soybean genotypes will present different patterns on root growth, and consequently, will vary in nutrient accumulation for both shoot and root parts. The objectives of this study were to: (i) characterize root length, surface area, average root diameter, and total root volume of two contrasting genotypes of corn and soybean using image analysis in the greenhouse and under field conditions; and (ii) evaluate dry weight biomass accumulation and nutrient uptake by shoot and root plant parts under a controlled greenhouse environment.