Maintaining winter wheat (Triticum aestivum L.) productivity with more efficient nitrogen (N) management will enable growers to increase profitability and reduce the negative environmental impacts associated with nitrogen loss. Wheat breeders would therefore benefit greatly from the identification and application of genetic markers associated with nitrogen use efficiency (NUE). To investigate the genetics underlying N response, two bi-parental mapping populations were developed and grown in four site-seasons under low and high N rates. The populations were derived from a cross between previously identified high NUE parents (VA05W-151 and VA09W-52) and a shared common low NUE parent, ‘Yorktown.’ The Yorktown × VA05W-151 population was comprised of 136 recombinant inbred lines while the Yorktown × VA09W-52 population was comprised of 138 doubled haploids. Phenotypic data was collected on parental lines and their progeny for 11 N-related traits and genotypes were sequenced using a genotyping-by-sequencing platform to detect more than 3,100 high quality single nucleotide polymorphisms in each population. A total of 130 quantitative trait loci (QTL) were detected on 20 chromosomes, six of which were associated with NUE and N-related traits in multiple testing environments. Two of the six QTL for NUE were associated with known photoperiod (Ppd-D1 on chromosome 2D) and disease resistance (FHB-4A) genes, two were reported in previous investigations, and one QTL, QNue.151-1D, was novel. The NUE QTL on 1D, 6A, 7A, and 7D had LOD scores ranging from 2.63 to 8.33 and explained up to 18.1% of the phenotypic variation. The QTL identified in this study have potential for marker-assisted breeding for NUE traits in soft red winter wheat.

The δ¹⁵N natural abundance technique is frequently used to quantify the proportion of legume nitrogen derived from atmospheric fixation (%Ndfa). This method compares the δ¹⁵N of a legume with a nonlegume reference plant to estimate the %Ndfa. For accurate estimations, it is recommended to pair each legume plot with a nonlegume reference plant to account for spatial variation. However, this pairing scheme is not feasible in large screening trials. Here, we tested the feasibility of eliminating reference plants to screen a faba bean (Vicia faba L.) population for %Ndfa. The first experiment screened 63 faba bean genotypes for %Ndfa by comparing estimates derived from an adjacent wheat (Triticum aestivum L.) reference plant in a nearest neighbor scheme (NN) with an arbitrary δ¹⁵N reference value (AR) of 7‰. Average and standard deviation of the genotypes’ %Ndfa were 58 ± 13% in 2019 and 72 ± 8% in 2020 using the NN model and 61 ± 11% in 2019 and 75 ± 7% in 2020 using the AR model. The AR model was able to identify a majority of the high and low %Ndfa genotypes in both years. In a second study, wheat and a dicot weed within the field were used as reference plants to estimate the %Ndfa. The weed reference plant resulted in 3 to 13% higher %Ndfa values compared with the wheat in three out of four testing environments, but the variation did not alter ranking of the genotypes for %Ndfa.

Cover cropping has been strongly promoted, but few growers have realized the benefits of this practice due to challenges linked to economic returns and whole-system management. In the western United States, winter legumes including faba bean have the potential to add economic value while offering soil health benefits compared with fallow fields. This experiment assessed the potential of five vegetable faba bean varieties for fresh pod yield, fresh pod quality, and biomass N return under a single and multiple pod harvest scheme. Vegetable faba bean varieties were further compared with two popular cover crop faba bean varieties, ‘Bell bean’ and ‘Sweet Lorane’ for cover crop and biomass N return benefits. The experiment revealed significant ( P ≤ 0.05) genotypic variation for vegetable fresh pod yield, dry biomass, fresh pod quality, pod N removal, biomass N return, and C:N in three testing environments under the single and multiple harvest schemes. Finally, the vegetable variety ‘Vroma’ produced high average fresh pod yield under the single (16,178 kg·ha ⁻¹ ) and multiple (38,928 kg·ha ⁻¹ ) harvest schemes while maintaining high biomass N return under the single (119 kg·ha ⁻¹ N) and multiple harvests (97 kg·ha ⁻¹ N) compared with the cover crop varieties (128 kg·ha ⁻¹ N). This experiment demonstrated that a single fresh pod harvest on an early and high yielding faba bean variety can generate economic returns while also providing cover crop benefits that are comparable to termination of a faba bean cover crop on the same date.

The growing regional and global interests in legume crops for cover cropping and sustainable agriculture has provided new opportunities for growers to incorporate faba bean (Vicia faba L.) into their production systems. Much of faba bean's potential, especially in the western United States, is rooted in its high N fixation potential compared with other cultivated legumes. However, faba bean production is currently hindered by existing markets, regional agronomic extension guides, and availability of regionally adapted cultivars. This experiment began the effort to bridge one of the three gaps by evaluating 63 regionally and globally derived plant materials for agronomic and N fixation traits in four environments in California's Central Valley. The experiment observed significant (P ≤ .05) genotype × environment interactions for all faba bean N and agronomic except % of N derived from the atmosphere, harvest index, and 100‐seed weight. Further, we found opportunities to leverage global germplasm to increase or decrease the 100‐seed weight and days to flowering in locally adapted plant materials. Finally, this experiment identified trait‐trait‐associations that provide both opportunities and challenges to improving screening efficiencies (e.g., link between N yield and 100‐seed weight in Chico2019 [r = 0.57; P ≤ .001] and in Fresno2020 [r = 0.51; P ≤ .001]). This work sets a framework for regional faba bean cultivar development work in the western United States.