Nitrogen Use Efficiency In Wheat Research Articles

Nitrogen use efficiency of wheat and canola from urea treated with different types of double inhibitors

Urease inhibitor (specifically, N-( n-butyl) thiophosphoric triamide, NBPT) and nitrification inhibitors (NIs) have been used to minimize nitrogen (N) loss from urea. However, their effects on improving crop N use efficiency (NUE) are usually inconsistent. A 2-year study was conducted to determine the best combination of NBPT and different NIs on urea that will maximize NUE while reducing nitrate leaching. Treatments consisted of untreated urea, NBPT-treated urea, and six types of (NBPT + NI)-treated urea that were surface applied at 80 kg N ha−1 on plots seeded to canola (2019) and wheat (2020) at Carman and Portage in Manitoba, Canada. Plots at Carman had lysimeters installed to measure leached water and nitrate. The sites had at least 35% lesser rainfall than climate normal during each growing season. At each site, average grain yields, N removal, and residual nitrate were not significantly different between untreated urea and inhibitor-treated urea. Over the 2 years, there was no significant benefit of NBPT or NBPT + NI on crop NUE at each site. Cumulative leached nitrate (19–40 kg N ha−1) did not differ significantly among urea treated with and without inhibitors. This is because >50% of the precipitation occurred when the effectiveness of NI had elapsed. Although NBPT and NI are known to reduce N losses to the atmosphere, this study suggests that the agronomic benefit and nitrate leaching prevention by NI applied in the spring may be limited in regions where large precipitation occurs later in the growing season or during non-growing season.

How Does Crop Rotation Influence Soil Moisture, Mineral Nitrogen, and Nitrogen Use Efficiency?

Rice–wheat (RW) cropping systems are integral to global food security. Despite being practiced for decades, Chinese RW cropping systems often suffer from low productivity and poor nitrogen use efficiency (NUE), reflecting management approaches that are not well-contextualized to region and season. Here, we develop the best management guides for N fertilizer in RW systems that are designed to help raise the productivity, NUE, and environmental sustainability of winter wheat over the long term. 2-year field experiments were conducted with four N fertilizer rates (0, 135, 180, and 225 kg N ha–1), allowing contrasts of yields, soil moisture, and NUE of wheat in RW in the humid climates zones on the Jianghan Plain. We compared RW systems with soybean/maize dryland wheat (DW) systems that are similarly endemic to China: after soybean/maize is harvested, soils are often drier compared with moisture content following rice harvest. With high seasonal N application rates (180–225 kg N ha–1), wheat crop yields increased by 24% in RW which were greater than comparable yields of wheat in DW, mainly due to greater kernels per spike in the former. Across treatments and years, N accumulation in plant tissue and kernel dry matter of DW was higher than that in RW, although mean agronomic efficiency of nitrogen (AEN) and physiological efficiency of nitrogen (PEN) of RW systems were greater. As N application rates increased from 135 to 225 kg ha–1, AEN and PEN of DW decreased but changed little for RW. Soil ammonium N was much lower than that of nitrate N; changes in NH4+ and NO3– as a consequence of increasing N fertilization were similar for RW and DW. We recommend that tactical application of N fertilizer continue seasonally until midgrain filling for both the DW and RW systems. At fertilization rates above 180 kg N ha–1, yield responses disappeared but nitrate leaching increased significantly, suggesting declining environmental sustainability above this N ceiling threshold. Collectively, this study elicits many functional and agronomic trade-offs between yields, NUE, and environmental sustainability as a function of N fertilization. Our results show that yield and NUE responses measured as part of crop rotations are both more robust and more variable when derived over multiple seasons, management conditions, and sites.

Genetic improvement analysis of nitrogen uptake, utilization, translocation, and distribution in Chinese wheat in Henan Province

Genetic improvement analysis of the nitrogen use efficiency (NUE) of wheat ( Tritium aestivum L.) was undertaken to determine the factors guiding NUE in order to develop new wheat cultivars with high yield, high NUE and high quality. To investigate the genetic improvement of wheat NUE and its components, 31 wheat cultivars that had been widely planted in Henan Province since 1941 were grown under high N treatment (HN) and low N treatment (LN). The results indicated that grain yield and NUE have increased significantly with cultivar development since 1941, with an annual genetic gain of 1.03% and 0.74%, respectively, under HN and LN. The significant increase in NUE mainly resulted from a significant increase in N uptake efficiency (NupE) and N utilization efficiency (NutE). NutE was the predominant component contributing to NUE under HN, while NupE was more important than NutE for NUE under LN. The improvement of NutE occurred at the expense of lower grain N content (GNC) as grain yield increased. Breeding was shown to increase N translocation (NTE) by an annual genetic gain of 1.33% and 0.33%, respectively, under HN and LN. N accumulation at the maturity stage was higher in the modern cultivars compared to the pre-modern cultivars, mainly as a result of increased N accumulation during the stem elongation phase. The N translocation capacity of the vegetative tissues increased, and the N translocation efficiency of the sheath and chaff were higher than that of the leaves. Important genetic improvement targets for high NUE include increasing pre-anthesis N assimilation ability and post-anthesis N translocation capacity. Furthermore improvements in wheat breeding should include increasing both N uptake and NHI to improve NUE and reverse the trend of declining GNC. • Higher genetic gain of grain yield and N use efficiency under better environment. • Modern cultivars had higher N accumulation, mainly raised during stem elongation phase. • N utilization efficiency increased at the expense of lower grain N content. • Enhanced N translocation and uptake was important for N use efficiency improvement.

Current Status and Future Prospective for Nitrogen Use Efficiency in Wheat (Triticum aestivum L.).

Although essential for achieving high crop yields required for the growing population worldwide, nitrogen, (N) in large amounts, along with its inefficient use, results in environmental pollution and increased greenhouse gas (GHG) emissions. Therefore, improved nitrogen use efficiency (NUE) has a significant role to play in the development of more sustainable crop production systems. Considering that wheat is one of the major crops cultivated in the world and contributes in high amounts to the large N footprint, designing sustainable wheat crop patterns, briefly defined by us in this review as the 3 Qs (high quantity, good quality and the quintessence of natural environment health) is urgently required. There are numerous indices used to benchmark N management for a specific crop, including wheat, but the misunderstanding of their specific functions could result in an under/overestimation of crop NUE. Thus, a better understanding of N dynamics in relation to wheat N cycling can enhance a higher efficiency of N use. In this sense, the aim of our review is to provide a critical analysis on the current knowledge with respect to wheat NUE. Further, considering the key traits involved in N uptake, assimilation, distribution and utilization efficiency, as well as genetics (G), environment (E) and management (M) interactions, we suggest a series of future perspectives that can enhance a better efficiency of N in wheat.

Effect of Nitrogen Levels on Use Efficiencies and Yield of Wheat at Bharatpur, Chitwan, Nepal

Improper nitrogen management and declining soil fertility are major constraints of wheat production in Nepal. Limited information is available on optimum nitrogen levels and use efficiencies. Therefore, a field experiment was conducted on November 2018 at the Inner Terai to determine the effect of nitrogen on yield and improve the nitrogen use efficiency of wheat. Levels of five nitrogen, 0 kg ha-1 (Control), 60 kg ha-1,80 kg ha-1, 100 kg ha-1 and 120 kg ha-1, were laid out in randomized complete block design (RCBD) with four replicates. Observations on growth parameters such as plant height (cm), tiller m-2 and yield attributing characteristics such as thousand grain weight (g), spike length (cm), and grain spike-1, were found to be highest at a nitrogen level of 120 kg ha-1. Nitrogen at 120 kg ha-1 increases the grain yield, straw yield and harvest index. The grain nitrogen concentration at 120 kg ha-1 was statistically similar to that at 100 kg ha-1 and 80 kg ha-1 while nitrogen uptake was highest (114. 833 kg ha-1) at 120 kg ha-1 and lowest in control. Agronomic use efficiency is highest at 100 kg ha-1 and lowest at 60 kg ha-1. The apparent fertilizer N 96 recovery percentage was high (49.62%) at 120 kg ha-1, which is statistically similar to 100 kg ha-1 (46.97%) and lowest (31.76%) at 60 kg ha-1. However, observing agro physiological efficiency and the nitrogen harvest index did not show any significant difference among treatments. The application of nitrogen at 120 kg ha-1 was required to produce the preferable yield and the nitrogen use efficiency traits.

Spatiotemporal Variation Characteristics and Driving Factors of Nitrogen Use Efficiency of Wheat–Rice Rotation Systems in the Taihu Lake Region

During the past three decades, a large amount of nitrogen (N) fertilizers has been applied in the rice and wheat rotation system in the Taihu Lake region of southern China to achieve high yield, resulting in low N use efficiency (NUE). China is implementing the national strategy “fertilizer reduction with efficiency increase” to solve the serious ecological problems caused by excessive fertilization. However, the effects of N fertilizer reduction on soil fertility and their integrated effect on NUE of rice–wheat rotation systems in the Taihu Lake region are not fully understood. In this study, test fields with different soil-fertility qualities were selected in typical rice–wheat areas in the Taihu Lake region to perform a 2-year rice–wheat N fertilizer effect test to obtain the comprehensive quantitative relationship among the integrated fertility index (IFI), nitrogen application level (NA), and NUE. Through the investigation and spatial analysis of NA and IFI in the study area in 2003 and 2017, the spatial and temporal variation characteristics of NA and IFI in the study area in the past 15-year period were obtained, and this information was spatially coupled with the comprehensive quantitative relationship model of NUE to reveal the variation characteristics and driving factors of NUE in the study area. The result shows that the wheat and rice NA in the study area in 2017 increased by 35.5 and 8.4%, respectively, compared with 2003. Due to excessive fertilization, the soil nitrogen, phosphorus, and potassium content of cultivated land in the study area in 2017 was greater than that in 2003, especially soil-available phosphorus and potassium contents, whereas soil organic matter (SOM) content was reduced. The cultivated land IFI of the study area as a whole increased by 7.2% in the 15-year period. The NUE of rice and wheat rotation increased by 5.8% in 2017 compared with that of 2003 due to the improvement in crop varieties and N fertilizer yield benefits. The increases of NA and IFI both have negative correlations with the NUE improvement, and the NA increase has a greater impact. In addition, the terrain, soil type, texture, and parent material also affect the soil nutrient-preserving capability and, thus, affect the spatial variation of IFI and NUE improvement. These factors have greater influence on NUE improvement of wheat than rice. This study provides a novel and effective method for analyzing the spatial-temporal variation characteristics of NUE in the rice–wheat system and is conducive to guide precise fertilization and N fertilizer reduction based on the spatial analysis of NA with IFI and NUE.

Impact of rice (O. sativa L.) straw incorporation induced changes in soil physical and chemical properties on yield, water and nitrogen–balance and –use efficiency of wheat (T. aestivum L.) in rice–wheat cropping system: Field and simulation studies

CONTEXTDeterioration of soil physico–chemical properties as a result of puddling and burning of rice straw is one of the big challenges for the farmers in Indo Gangetic plains. OBJECTIVETo study the impact of rice straw incorporation persuaded changes in soil properties on yield, water and nitrogen use efficiency of wheat in rice–wheat cropping system. METHODSA field experiment, with split plot design and replicated thrice, was conducted with treatment combinations of four rates of rice straw incorporation, Rsti (0, 5, 7.5, 10 t ha−1) as main plots and four rates of fertilizer nitrogen, N (0, 90, 120 and 150 kg ha−1) as sub plots for ten years. Simulations with same treatments of Rsti and N along with three irrigation regimes, IW (240, 320 and 400 mm) were carried out for 30 years with calibrated and validated DSSAT–CSM–CERES–Wheat v4.75 model. RESULTS AND CONCLUSIONSThe results of field experimentation and model showed that the significant effect of Rsti on wheat yield was up to 7.5 t ha−1; Comparable yield to recommended practices (without crop residue) was realized with Rsti in conjunction with less IW and N, ensuing saving of 80 mm IW plus 30 kg N ha−1. Rsti increased water use efficiency via reducing evapotranspiration; and increased nitrogen recovery efficiency by increasing N uptake, and decreasing N leaching and NH3 losses. SIGNIFICANCEThe model based simulations signifies that Rsti into surface soil is a viable option in India and IGP as it enhances yield, water and nitrogen use efficiencies in wheat of rice–wheat system.

Effect of Legumes on Nitrogen Use Efficiency of Wheat in a Short Term Crop Rotation in Njoro Sub-County

Aims: The study determined the effect of legumes in short term crop rotation (cereal – legumes cropping systems) on nitrogen use efficiency of wheat.
 Study Design: A randomized complete block design (RCBD) was used in a split-split-plot arrangement replicated three times. Three factors evaluated included water harvesting (WH), crop rotation (CR) and soil fertility management (SFM). The data obtained were subjected to an analysis of variance (ANOVA) using Genstat statistical package while the mean separation was performed using least significance differences (P =.05).
 Place and Duration of Study: The trial was conducted at the Kenya Agricultural and Livestock Research Organization (KALRO) fields based in Njoro for three years between 2014 and 2016 during rainy seasons.
 Methodology: The treatments consisted of four pre-crops in the rotation systems (CR1 = Dolichos lablab (L. purpureus) as a pre-crop; CR2 = Green pea (Pisum sativum) as a pre-crop; potato (Solanum tuberosum) as a pre-crop; and CR4 = continuous wheat (Triticum aestivum), two water harvesting (WH) strategies (WH = flat beds; and WH= tied ridges) and six soil fertility management (SFM) strategies (SFM1 = untreated control; SFM2 = FYM at 5 t ha-1; SFM3 = Green manure (Leucaena trichandra) at 2.5 t ha-1; SFM4 = inorganic source at 25 kg N ha-1; SFM5 = inorganic source at 50 kg N ha-1; and SFM6 = Inorganic source at 75 kg N ha-1)..
 Results: The results revealed that the value of NUE significantly (p < 0.001) increased when P. sativum and L. purpureus preceded wheat in the short term crop rotation system. The value of NUE increased by 39% and 44%, when wheat was preceded L. purpureus and P. sativum, respectively, relative to S. tuberosum. Under continuous wheat, NUE value was increased by 54.17% relative to potato as a pre-crop. Overall, the contribution of legumes (L. purpureus and P. sativum) as precursor crops was greater than those observed with potato and wheat as pre-crops.

Effects of Fertilization on Yield and Nitrogen Use Efficiency of Wheat and Rice with Straw Return

ABSTRACT Fertilizer application of controlled-release urea (CRU) is a feasible fertilization method because of its simple operation, high efficiency, environmental friendliness, and labor-saving. However, the high cost of CRU and the dynamic change of nitrogen (N) demand caused by straw return make it necessary to find a better fertilization method. Therefore, we investigated the effects of application of the mixed CRU and urea on the yield and nitrogen use efficiency (NUE) of wheat and rice, and soil fertility with straw return. The results indicated that application of the mixed CRU and urea increased the yield of wheat and rice compared with 100% urea application. The maximum increments of yield of wheat and rice occurred in the substitution ratio of CRU with 50%. Reducing N application rate of the mixed CRU and urea in wheat by 20% and rice by 15% also increased the yield of wheat and rice compared with 100% urea. Applying the mixed CRU and urea increased NUE of wheat and rice, compared with 100% urea. The maximum increments of NUE of wheat and rice were 31.9% and 37.4%, respectively. Reducing N application rate of the mixed CRU and urea could further increase NUE of wheat and rice. Compared with 100% urea, applying the mixed CRU and urea increased soil organic carbon, total N, alkaline N, and urease concentration. In summary, application of the mixed CRU and urea is feasible to achieve stable crop yield and to improve NUE with straw return. In addition, the application of CRU requires less N fertilizer application. Therefore, application of mixed CRU and urea is of great significance to ensure national food security and sustainable agricultural development.

Optimal Blends of Controlled-Release Urea and Conventional Urea Improved Nitrogen Use Efficiency in Wheat and Maize with Reduced Nitrogen Application

Blending controlled-release urea (CRU) with conventional urea has the potential to be an effective option for improving nitrogen (N) use efficiency (NUE), although determination of optimal blends in combination with a reduced N application rate has not been well studied. A field experiment was conducted to compare the effects of CRU (a mixture of polymer-coated urea and urea with N ratios of 100:00, 75:25, and 50:50 at 144 kg N ha−1, hereafter denoted as CRU1, CRU2, and CRU3, respectively), urea at 180 (U1) and 144 kg N ha−1 (U2) and a control (no N fertilizer applied, CK) on grain yield, NUE, and economic benefits in a wheat–maize rotation system. The CRU treatments were one-time applied, while for the U treatments, fertilizer N was applied in a split application. The results suggest that a one-time application of CRU prior to sowing of both crops fulfilled the demand of crop plants for N across the entire growth period. Relative to U1, the CRU treatments achieved approximately the same grain yield and 4.7–26.6% greater NUE at 20% reduced N application. Moreover, under CRU2, the yield, NUE, and economic benefits were increased by 12.2%, 9.7%, and 19.1%, respectively, for wheat, and under CRU3, they were increased by 10.9%, 20.6%, and 17.3%, respectively, for maize, compared with the U2 treatment. These results demonstrate that a mixture of CRU and urea at a ratio of 75:25 for wheat and 50:50 for maize with a 20% reduction in N application rate can maintain productivity, while enhancing NUE in the North China Plain.

From South Asia to the world: embracing the challenge of global sustainable nitrogen management

From South Asia to the world: embracing the challenge of global sustainable nitrogen management

Opportunities for Increased Nitrogen Use Efficiency in Wheat for Forage Use.

Wheat is a major cool-season forage crop in the southern United States. The objective of this study is to understand the effect of nitrogen (N) fertilization on wheat biomass yield, quality, nitrogen use efficiency (NUE), and nitrogen nutrition index (NNI). The experiments were conducted in a greenhouse and a hoop house in a split-plot design, with three replications. Twenty wheat cultivars/lines were evaluated at four N rates (0, 75, 150, and 300 mg N.kg−1 soil) in the greenhouse and (0, 50, 100, and 200 mg N.kg−1 soil) in the hoop house. In general, high-NUE lines had lower crude protein content than the low-NUE lines. None of the cultivars/lines reached a plateau for biomass production or crude protein at the highest N rate. The line × N rate interaction for NUE was not significant in the greenhouse (p = 0.854) but was highly significant in the hoop house (p < 0.001). NNI had a negative correlation with NUE and biomass. NUE had strong positive correlations with shoot biomass and total biomass but low to moderate correlations with root biomass. NUE also had a strong positive correlation with N uptake efficiency. Lines with high NUE can be used in breeding programs to enhance NUE in wheat for forage use.

Nitrous oxide emissions and nitrogen use efficiency in wheat: Nitrogen fertilization timing and formulation, soil nitrogen, and weather effects

AbstractImproving N fertilization in croplands could minimize soil emissions of nitrous oxide (N2O) and mitigate climate change. This study investigated the effects of spring vs. fall N applications of conventional vs. enhanced‐efficiency N fertilizers (EENFs) on N2O emissions and N use efficiency in spring wheat (Triticum aestivum L.) over 2.5 yr in Alberta, Canada. Fertilizers were anhydrous ammonia and urea and the EENF formulations included urease and nitrification inhibitors and a polymer coating. We measured a fertilizer N2O emission factor of 0.31 ± 0.04%. Irrespective of N fertilizer and timing options peak N2O emissions were evident following soil thawing and major rainfalls. Because most of the annual N2O emissions were associated with soil thawing, spring‐applied N emitted half the N2O of the fall‐applied N during the second study year (P &lt; .001). Conversely, the opposite was observed for the first study year when overall N2O emissions were 36% larger for spring‐ than fall‐applied N (P = .031) as major rainfalls occurred shortly after the spring N fertilization. Nevertheless, within this first study year, EENFs significantly reduced N2O emissions (by 26% on average; P = .019), with a tendency for 11% higher grain yield across springtime EENFs than for conventional fertilizers. Concomitantly, spring‐applied N doubled the fertilizer N recovery efficiency in the same year (P = .023). The soil at the study site inherently had high N availability (NH4 and NO3) and this probably moderated the beneficial effects of EENFs on N2O emissions and grain yields. Results suggest that spring EENFs can mitigate the risk for N2O emissions while sustaining high yields even under scenarios with high availability of native soil N.

Estimation of leaf nitrogen content and photosynthetic nitrogen use efficiency in wheat using sun-induced chlorophyll fluorescence at the leaf and canopy scales

Leaf nitrogen content (LNC), an indicator for the amount of photosynthetic proteins, plays an important role to understand plant function and status. In previous studies, vegetation indices (VIs) have been demonstrated to monitor LNC non-destructively, but which is influenced by backgrounds, and lacks specificity for nitrogen stress. In this study, sun-induced chlorophyll fluorescence (SIF), a novel technique related to plant physiology state, was proposed to estimate area-based and mass-based LNC at both leaf and canopy scales. In addition, SIF indices were evaluated to retrieve photosynthesis nitrogen use efficiency (PNUE), an important trait of leaf economics and physiology, based on the relationships between SIF, photosynthesis, and LNC.This study was conducted on two field experiments of winter wheat with different nitrogen regimes in Rugao, Jiangsu Province, China during 2016-2017 and 2017-2018 growing seasons. We took measurements of SIF, reflectance, biochemical and growth structural parameters at the leaf and canopy scales. The SIF signal was collected using ASD (Analytical Spectral Devices, Boulder, CO, USA) and QEpro (Ocean Optics, Dunedin, FL, USA) spectrometers at the two observational scales, with a full width at half maximum (FWHM) of 1.4 nm and 0.13 nm, respectively. SIF indices were calculated based on the SIF signal extracted at two oxygen absorption bands. Our results demonstrated that area-based LNC was better related to SIF indices and VIs than mass-based LNC. SIF ratio index (SIFR) and normalized SIF index (SIFN), defined as SIF761/SIF687 and (SIF761-SIF687)/(SIF761+SIF687) separately, performed better in monitoring area-based LNC at the two observation scales than CIred edge, which performed best in VIs group. Compared with CIred edge, the best estimation accuracy of SIF indices for area-based LNC increased by 0.08 and 0.02 at the leaf and canopy scales, separately. And when using SIFR and SIFN to monitor area-based LNC, there is no saturation phenomenon, which occurs using traditional VIs. From the whole range of data, area-based LNC was closely related to several plant traits (leaf: area-based leaf chlorophyll content (LCC) (LCCarea), leaf mass per area (LMA); canopy: area-based canopy LCC (CCCarea), leaf area index (LAI), leaf dry weight (LDW) per unit soil area, and LMA), which was consistent with previous studies. However, in specific group with fixed area-based LCC value, although area-based LNC almost wasn’t significantly correlated with these traits, SIFR and SIFN were instead always highly correlated with area-based LNC in each small datasets on two observation scales (leaf scale: R2>0.50, R2>0.46; canopy scale: R2>0.41, R2>0.42). Thus, the contribution of SIFR and SIFN to estimate area-based LNC wasn’t only the plant traits listed, but also other internal characters, like nitrogen allocation and proportion. Moreover, SIFR and SIFN were proved to be potential detectors to retrieve PNUE. These findings would provide us a new perspective for understanding plant nitrogen status from remote sensing observations, detecting plant function and managing precise agriculture.

Long-Term Nitrogen Fertilization Impacts on Soil Bacteria, Grain Yield and Nitrogen Use Efficiency of Wheat in Semiarid Loess Plateau, China

Soil bacteria are key components of the soil microbial community contributing to soil health. Nitrogen (N) fertilization is an important factor that affects soil microbial community and cereal production. This study aims to explore the impact of long-term N fertilization on soil bacterial diversity, nitrogen use efficiency (NUE), and the grain yield of wheat in the semiarid region of Loess Plateau, China. The field experiment was conducted from 2003 to 2018 including five N treatments: 0 (N0), 52.5 (N52.5), 105 (N105), 157.5 (N157.5), and 210 (N210) kg N ha−1 yr−1. The soil pH was decreased by the N fertilization, while the soil ammonium, nitrate, and available phosphorus were increased. The N uptake and grain yield of wheat were significantly increased with N and the highest NUE (28%) and grain yield (44% higher than control) were observed at 105 kg N ha−1, but no significant increase in yield was observed by further increasing N rate. The bacterial diversity was significantly increased at N105. Soil bacteria community was strongly related to soil chemical properties and ammonium content was the most important contributor. The dominant soil bacterial phyla were Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi, Gemmatimonadetes, Bacteroidetes, Nitrospirae, Verrucomicrobia, and Planctomycetes. The higher grain yield of wheat was related to the higher class Gammaproteobacteria and Sphingobacteriia abundance, and lower class Acidobacteria and Chloroflexia abundance. In summary, 105 kg ha−1 yr−1 was the optimum rate of N for diversified soil bacterial community and wheat yield for sustainable wheat production in semiarid Loess Plateau of China, whose higher N use efficiency was attributed to the higher phyla Verrucomicrobia and Planctomycetes, and lower Proteobacteria abundance.

Review of Active Optical Sensors for Improving Winter Wheat Nitrogen Use Efficiency

Improvement of nitrogen use efficiency (NUE) via active optical sensors has gained attention in recent decades, with the focus of optimizing nitrogen (N) input while simultaneously sustaining crop yields. To the authors’ knowledge, a comprehensive review of the literature on how optical sensors have impacted winter wheat (Triticum aestivum L.) NUE and grain yield has not yet been performed. This work reviewed and documented the extent to which the use of optical sensors has impacted winter wheat NUE and yield. Two N management approaches were evaluated; optical sensor and conventional methods. The study included 26 peer-reviewed articles with data on NUE and grain yield. In articles without NUE values but in which grain N was included, the difference method was employed to compute NUE based on grain N uptake. Using optical sensors resulted in an average NUE of 42% (±2.8% standard error). This approach improved NUE by approximately 10.4% (±2.3%) when compared to the conventional method. Grain yield was similar for both approaches of N management. Optical sensors could save as much as 53 (±16) kg N ha−1. This gain alone may not be adequate for increased adoption, and further refinement of the optical sensor robustness, possibly by including weather variables alongside sound agronomic management practices, may be necessary.

Impacts of G x E x M on Nitrogen Use Efficiency in Wheat and Future Prospects.

Globally it has been estimated that only one third of applied N is recovered in the harvested component of grain crops. This represents an incredible waste of resource and the overuse has detrimental environmental and economic consequences. There is substantial variation in nutrient use efficiency (NUE) from region to region, between crops and in different cropping systems. As a consequence, both local and crop specific solutions will be required for NUE improvement at local as well as at national and international levels. Strategies to improve NUE will involve improvements to germplasm and optimized agronomy adapted to climate and location. Essential to effective solutions will be an understanding of genetics (G), environment (E), and management (M) and their interactions (G x E x M). Implementing appropriate solutions will require agronomic management, attention to environmental factors and improved varieties, optimized for current and future climate scenarios. As NUE is a complex trait with many contributing processes, identifying the correct trait for improvement is not trivial. Key processes include nitrogen capture (uptake efficiency), utilization efficiency (closely related to yield), partitioning (harvest index: biochemical and organ-specific) and trade-offs between yield and quality aspects (grain nitrogen content), as well as interactions with capture and utilization of other nutrients. A long-term experiment, the Broadbalk experiment at Rothamsted, highlights many factors influencing yield and nitrogen utilization in wheat over the last 175 years, particularly management and yearly variation. A more recent series of trials conducted over the past 16 years has focused on separating the key physiological sub-traits of NUE, highlighting both genetic and seasonal variation. This perspective describes these two contrasting studies which indicate G x E x M interactions involved in nitrogen utilization and summarizes prospects for the future including the utilization of high throughput phenotyping technology.

A wheat transcription factor positively sets seed vigour by regulating the grain nitrate signal.

Summary Seed vigour and early establishment are important factors determining the yield of crops. A wheat nitrate‐inducible NAC transcription factor, TaNAC2, plays a critical role in promoting crop growth and nitrogen use efficiency (NUE), and now its role in seed vigour is revealed. A TaNAC2 regulated gene was identified that is a NRT2‐type nitrate transporter TaNRT2.5 with a key role in seed vigour.Overexpressing TaNAC2‐5A increases grain nitrate concentration and seed vigour by directly binding to the promoter of TaNRT2.5‐3B and positively regulating its expression. TaNRT2.5 is expressed in developing grain, particularly the embryo and husk.In Xenopus oocyte assays TaNRT2.5 requires a partner protein TaNAR2.1 to give nitrate transport activity, and the transporter locates to the tonoplast in a tobacco leaf transient expression system. Furthermore, in the root TaNRT2.5 and TaNRT2.1 function in post‐anthesis acquisition of soil nitrate. Overexpression of TaNRT2.5‐3B increases seed vigour, grain nitrate concentration and yield, whereas RNA interference of TaNRT2.5 has the opposite effects. The TaNAC2‐NRT2.5 module has a key role in regulating grain nitrate accumulation and seed vigour. Both genes can potentially be used to improve grain yield and NUE in wheat.

Combining breeding traits and agronomic indicators to characterize the impact of cultivar on the nitrogen use efficiency of bread wheat

Nitrogen (N) is an essential compound for the production and grain quality of bread wheat, which must respect market requirements. Improving nitrogen use efficiency (NUE) is a priority to better manage nitrogen for the benefit of farm economy and the environment. Among all the available levers to do this, the choice of the right cultivar is crucial. To this end, an accurate NUE cultivar characterization is needed both for breeding programmes and for agronomic extension services dedicated to advise farmers. These two fields of expertise (genetic and agronomy) do not share exactly the same protocols and indicators to assess the impact of cultivar on wheat NUE. Moreover, although some recent NUE genetic studies have been conducted on cultivars currently available in France, no recent NUE agronomic studies have been made on current French wheat cultivars. Moreover, the latest agronomic studies to date on cultivar effect on wheat N requirement (coefficient “b” used in France) were conducted without considering the need to reach a grain protein concentration of 11.5% (French bread wheat market requirement) in addition to the objective of achieving the yield potential. By using a classical agronomic protocol (network of 12 field trials over 3 years testing bread-wheat cultivars along a complete nitrogen response curve), the presented study aimed to address three specific NUE related topics by characterizing recent French cultivars with a large range of NUE indicators used by geneticists and/or agronomists. Firstly, we demonstrated that N rate and recent French cultivars had a significant effect on NUE and its components (nitrogen uptake efficiency – NupE and nitrogen utilization efficiency – NutE), as well as on apparent fertilizer recovery (AFR). Secondly, we showed that NupE and AFR were strongly correlated, allowing us to compare genetic studies (mainly using NupE) and agronomic studies (mainly using AFR) without any difficulty. Thirdly, we designed a set of new N requirement indicators (coefficients “bc” and “bq”) helping the farmer to grow each bread wheat cultivar with a dual objective of optimum yield and grain protein content in line with the market requirements. This could be achieved without significant impact on nitrogen post-harvest losses. The presented study provides a large set of results, usable for breeding and agronomic research programs.

Modeling crop yield and nitrogen use efficiency in wheat and maize production systems under future climate change

In the face of global climate change, changes in nitrogen use efficiency (NUE) have not been widely considered to affect agricultural productivity. A modeling study was conducted to assess the impacts of future climates on crop yields and NUE in two wheat (Triticum aestivum L.) and maize (Zea mays L.) rotation systems and one continuous maize system in northern China. Specifically, the process-based SPACSYS model was used to predict crop yields and NUE by 2100, under four climate scenarios (Baseline, RCP2.6, RCP4.5 and RCP8.5). The model was validated using data from three long-term experiments, each of which included four fertilization practices typical of the regions: non-fertilizer, combined mineral N, phosphorus (P) and potassium (K) (NPK), NPK plus manure and NPK plus straw. Validation showed SPACSYS well-simulated crop yields and N uptake (R2: 0.41–0.96; RMSE: 6–18%; and EF: 0.41–0.93). Under future climate change, the model predicted changes in maize yield by − 30.69% and 5.98% in northwestern and northeastern China, respectively, and wheat yield by − 16.37% in northwestern China. Future climates would cause greater NUE reductions in the northwest (wheat: 42.79%; maize: 33.73%) than in the northeast (maize: 3.97%) with smaller decreases in crop N uptake and N loss. Furthermore, manure application had higher crop NUEs (wheat: 6.66–31.27%; maize: 23.82–68.19%) and N uptakes than other treatments under future climate change. The results demonstrated the risks of future climate changes on crop yield and NUE in the study regions and can also help target fertilization practices for effectively mitigating climate change.