Top-Soil Root Architecture Characteristics of Obsolete and Modern Soybean Cultivars and Shoot and Seed Nutrient Contents.

Roots anchor the plant and are vital for plant water and nutrient acquisition. The spatial arrangement of roots in the soil influence plants ability to explore soil resources and is a function of numerous traits, including branching, angles, numbers, and lengths of the various root types composing the whole root system. Soybean yield has improved significantly over years of breeding. However, the relationship between the root architecture, nutrient uptake, and yield as a function of year of cultivar release is unclear. The objective of this study was to examine the relationship between soybean root architecture and year of cultivar release as well as the relationship with nutrient uptake and accumulation in shoot tissue and seeds. Experiments were conducted in 2016 at two locations near Columbia MO with 24 cultivars ranging in year of release (YOR) from 1930 to 2005. When plants reached the seed filling stage (R5), root systems of five plants per plot were excavated from the topsoil to assess root architecture. Aboveground biomass was assessed at the same time and processed and analyzed for mineral nutrients. At maturity, seeds were harvested and a subsample analyzed for mineral nutrients. The results showed that several root architecture traits have changed with respect to YOR, including positive correlations of overall root complexity scores and lateral root number with YOR. Overall root complexity scores were positively correlated with the phosphorus concentration in shoot tissue and with the contents of macro- and micronutrients in seeds. In general, negative correlations between YOR and seed macro- and micronutrient concentrations were found; however, shoot nutrient concentrations were not related with YOR. Results indicate that breeding for increased yield altered top soil root architecture and nutrient uptake of soybean cultivars; however, the extent to which the changes in root system architecture underlie greater yields of modern cultivars remains to be investigated.