Increased application of nitrogen fertilizers has significantly raised grain yield and protein concentration in wheat. However, only 30–50% of applied fertilizer nitrogen are usually utilized by the plant. In this study, four soft red winter wheat genotypes (Triticum aestivum L., IL07‐4415, MD05W10208‐11‐8, OH06‐150‐57 and Sisson) were grown under three different nitrogen regimes (high, medium, and low) in a greenhouse, and grain yield, grain protein concentration, nitrogen use efficiency (NUE) and their associated traits were evaluated. Among the four genotypes, a high‐yielding cultivar, Sisson, exhibited superior performance in terms of grain weight plant−1 and NUE for yield (NUEY) at low nitrogen due to maintained grain number spike−1 and harvest index. Significant yield losses due to nitrogen limitation were attributable to reduced spike number plant−1 and grain number spike−1 in the other genotypes. Interestingly, a linear relationship between NUEY and NUE for grain protein (NUEP) was detected at high (R2 = 0.67) and low (R2 = 0.42) nitrogen; both of these traits were positively correlated with grain number spike−1, 1000‐seed weight, and harvest index under nitrogen‐limited conditions (R2 = 0.35–0.48). These results suggest that simultaneous improvement of NUEY and NUEP could be achieved through the selection of the three yield components (grain number spike−1, 1000‐seed weight, and harvest index) at low nitrogen.

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.

Optimal N application is critical to ensure profitable soft red winter wheat (Triticum aestivum L.) production and limit negative environmental effects. This study was conducted using 12 wheat lines grown in two Ohio and six Virginia environments to determine the effects of differentially split N rates on grain yield, yield components, and N‐related traits. Upon analysis of wheat lines in two contrasting photoperiod groups, it was discovered that wheat lines containing the photoperiod sensitivity allele (Ppd‐D1b) conferred a significant (P < 0.05) yield advantage under N‐limited conditions in Ohio and across N treatments in half of the Virginia testing environments. This resulted from increased harvest index, grains per square meter, number of kernels per spike, and floret fertility in Ppd‐D1b lines relative to lines with the insensitive allele (Ppd‐D1a). However, wheat genotypes in the photoperiod‐insensitive allelic group had significantly higher (P < 0.05) grain N concentration in all Virginia testing sites. A spring split N application of 33 kg N ha−1 at Zadoks growth stage (GS) 25 and 101 kg N ha−1 at Zadoks GS 30 produced the highest grain yields and grain N contents in five of the six Virginia environments. Nitrogen utilization efficiency was the primary contributor to variation in N use efficiency under higher N rates, whereas N uptake efficiency was the greatest contributor under low N rates. The contribution of N utilization and uptake efficiencies varied among wheat lines in the Ppd‐D1a group when 67 kg N ha−1 was applied at Zadoks GS 25 under the moderate and standard N rates.

Soft red winter wheat (Triticum aestivum L.) production relies on efficient nitrogen (N) fertilization to maximize grower profitability and mitigate environmental impacts. Therefore, a panel of 11 elite wheat lines were grown as a randomized complete block design in four environments under low (LN) and high (HN) N rates to: (i) assess the genotypic variation in aboveground biomass (AGBM) and N yield (AGNY) throughout the growing season; and (ii) investigate the associations between yield and N‐related traits with AGBM and AGNY at tillering, booting, anthesis, and physiological maturity. Biomass samples were cut at the soil level and dried at four developmental stages to determine AGBM then ground to estimate AGNY for each sample. Significant genotypic variation (P ≤ 0.05) was observed for grain yield, grain N content, and N‐utilization efficiency in all testing environments. Additionally, significant (P ≤ 0.05) variation for AGBM and AGNY was identified at the five‐tiller stage, booting, anthesis, and physiological maturity in one or more testing environments. Grain yield was not significantly correlated with any trait under LN conditions despite expressing significant association with N‐utilization efficiency, N‐harvest index, AGBM at anthesis, and AGNY at anthesis under HN rates. Significant correlations also were identified for traits between LN and HN rates including AGBM at anthesis (r = 0.93, P < 0.001) and AGNY (r = 0.69, P < 0.01). Our results suggest that breeders can improve grain yields by using AGBM at anthesis as a proxy trait. Core Ideas Genotypic variation was observed in grain yield and N content, N‐utilization, biomass, and N yield. Grain yield correlated with aboveground biomass and aboveground N yield at anthesis under high N rates. Breeders can improve yields by using biomass at anthesis as a proxy trait per its strong correlation with N rates.

The δ 15 N natural abundance technique is frequently used to quantify the proportion of legume nitrogen derived from atmospheric fixation (%Ndfa). This method compares the δ 15 N 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 δ 15 N 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.

Faba bean (Vicia faba L.) cultivars for cover cropping have remained unchanged in the western United States over the past century. Although breeding efforts have improved grain production across much of the world, improvement of the crop for cover crop applications (e.g., biomass production at the flowering stage) remains understudied. Therefore, a trial of nine newly developed faba bean lines from the USDA‐ARS and four commercial checks (‘Bell Bean’, ‘V4’, ‘V5’, and ‘Windsor’) was established to evaluate cover crop traits across six diverse testing environments. The experiment revealed significant genotype × environment interactions for winter vigor, nitrogen (N) concentration, and aboveground N yield. Significant genotypic variation was observed for important cover crop traits including winter vigor, spring vigor, aboveground biomass, and aboveground N yield, whereas variation for percentage of N derived from the atmosphere was primarily determined by the testing environment. The study also identified a strong association between early plant vigor and aboveground biomass (r = .71), which offers potential increases in breeding efficiencies. In addition, advanced faba bean lines from the USDA‐ARS were shown to produce twice the biomass of Bell Bean across testing environments, and faba bean line PS18301 produced at least 20% more aboveground N yield in five out of the six environments than the conventionally used cover crop cultivars Windsor and Bell Bean. Faba bean lines in this study may be used by cover crop breeders as parent materials.

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. INTRODUCTIONA deeply intertwined interest in sustainable food systems and compatible specialty markets continues to grow in the western United States which opens the door for the plant breeders to reassess the potentials of once orphaned food crops. Among crop species, legumes have great potential for sustainable agricultural systems due to their value for human consumption Abbreviations: %Ndfa, N derived from the atmosphere.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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