Soybean Nitrogen Uptake and Utilization in Argentina and United States Cultivars

Abstract

1153 RESEARCH S oybean [Glycine max (L.) merr.] seed yield has been increasing between 0.5 and 1% per year during the last 20 years in the United States (Specht et al., 1999). Approximately 50% of this increase is due to genetic improvement while the other 50% is attributed to better management practices (Duvick, 2005;Egli, 2008;Specht et al., 1999). Future yield increases must continue to come, at least partially, from genetic improvement.A more rapid rate of genetic gain could be achieved through increased interaction between crop physiologists and plant breeders (Cooper and Hammer, 2005;Duvick, 2005;Hammer et al., 2006). Traditional breeding of autogamous species is an empirical ABSTRACT Crop production increase needed to satisfy a growing world population depends, at least partially, on increasing current genetic gain in yield. Theory proposes that increased genetic gain can be attained using diverse high-yielding parents. Physiological traits, compared to molecular or morphological markers, are hypothesized to better estimate parental diversity. A trait-based hybridization approach will require assessing diversity for physiological traits. Here, we phenotyped several traits using two physiological frameworks to assess diversity in 25 and 65 elite cultivars from Argentina (ARG) and the United States (USA), respectively. First, we identified the highest-yielding cultivar clusters across two environments in each country. These cultivars had the highest N uptake at both ARG and USA. Therefore, there was no genotypic diversity for total N uptake within each cluster. For other traits, the highest yielding clusters did not show the highest values. There was residual diversity within ARG and USA highest yielding clusters in the temporal pattern of N uptake, N use efficiency, and N harvest index. Stacking these traits in one cultivar could potentially increase yield by 13%. The possibility of such stacking, however, depends on the nature of the phenotypic correlation among traits. We demonstrated that several trade-off correlations between phenotyped traits, thought to hinder stacking, are actually not biologically based.

Physiological and management factors contributing to soybean potential yield

“…While yield is correlated with biomass accumulation, N accumulation can often explain more yield variation than biomass accumulation (Rotundo et al, 2014;Sinclair and Jamieson, 2006). Although there were no differences in total N accumulation among a group of high yielding cultivars, there were differences in their timing of N accumulation (Rotundo et al, 2014).…”

“…The self-destruct hypothesis also explains why a lower DMAC (or ISGR) increases the EFP by slowing the daily demand for C and N remobilization (Salado-Navarro et al, 1986a, 1986b, 1993. Diversity for N accumulation during seedfill and N remobilization among high-yielding elite cultivars may provide an avenue for increasing the EFP by delaying senescence (Rotundo et al, 2014).…”

“…Rotundo et al (2014) also documented diversity and alternate strategies among high yielding cultivars for N use efficiency (NUE), N harvest index, seed N, and HI. Rotundo et al (2014) suggested that breeding for increased NUE and HI with the average N accumulation rate held promise to increase yield ∼500 kg ha −1 in their environment. This indicates that the combination of increased N accumulation rates, NUE, and HI may hold potential for increasing yield even further.…”

Exploring soybean management options for environments with contrasting water availability

“…Nitrogen use efficiency was estimated as the ratio between total aboveground biomass and total canopy N uptake following Rotundo et al. ().…”

“…Under well‐watered environments, higher total N uptake can be obtained by N 2 fixation and direct soil absorption combinations (Santachiara, Borrás, Salvagiotti, Gerde, & Rotundo, ). Furthermore, soybean cultivars with superior yield involve not only higher N canopy uptakes but also higher N use efficiency and harvest index combinations (Rotundo, Borrás, de Bruin, & Pedersen, ). This theoretical framework can help explain yield differences associated with management options under contrasting water availabilities.…”