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Nitrogen is one of the most important macronutrients for crop growth and metabolism. To identify marker-trait associations for complex nitrogen use efficiency (NUE)-related agronomic traits, field experiments were conducted on nested synthetic wheat introgression libraries at three nitrogen input levels across two seasons. The introgression libraries were genotyped using the 35K Axiom® Wheat Breeder's Array and genetic diversity and population structure were examined. Significant phenotypic variation was observed across genotypes, treatments, and their interactions across seasons for all the 22 traits measured. Significant positive correlations were observed among grain yield and yield-attributing traits and root traits. Across seasons, a total of 233 marker-trait associations (MTAs) associated with fifteen traits of interest at different levels of nitrogen (N0, N60, and N120) were detected using 9,474 genome-wide single nucleotide polymorphism (SNP) markers. Of these, 45 MTAs for 10 traits in the N0 treatment, 100 MTAs for 11 traits in the N60 treatment, and 88 MTAs for 11 traits in the N120 treatment were detected. We identified putative candidate genes underlying the significant MTAs which were associated directly or indirectly with various biological processes, cellular component organization, and molecular functions involving improved plant growth and grain yield. In addition, the top 10 lines based on N response and grain yield across seasons and treatments were identified. The identification and introgression of superior alleles/donors improving the NUE while maintaining grain yield may open new avenues in designing next generation nitrogen-efficient high-yielding wheat varieties.

A 4 years field study was conducted to improve nitrogen (N) and phosphorus (P) use efficiencies in wheat (Triticum aestivum L.) using arbuscular mycorrhizal fungi (AMF) and precision N management. Split plot design was employed to rationalize N and P fertilizer use in two different experiments with AMF in the main plot and fertilizer application practice in the subplots. The AMF seed coating improved mycorrhization, root dry weight and P uptake. AMF coating of wheat seeds improved mean grain yield and agronomic efficiency of applied P fertilizer (AEP) by 11% and 55.4%, respectively. However, AMF seed coating did not improve chlorophyll content, normalized difference vegetative index, grain yield and agronomic efficiency of applied N fertilizer (AEN). Precision N management using leaf color chart (LCC), chlorophyll meter (SPAD), and GreenSeeker optical sensor (GS) sustained wheat grain yield equivalent to the soil-test based N fertilizer recommendation with 20–31 kg ha−1 less fertilizer N. Proximal sensing guided N use improved AEN by 21.9%–39.6% while mitigating global warming potential by 16%–24%. Integrated use of AMF seed coating and precision N management provides a potential solution to improve N and P nutrition and reduce environmental footprints of fertilizer N use in wheat. [ABSTRACT FROM AUTHOR]

Nitrogen is one of the most important macronutrients for crop growth and metabolism. To identify marker-trait associations for complex nitrogen use efficiency (NUE)-related agronomic traits, field experiments were conducted on nested synthetic wheat introgression libraries at three nitrogen input levels across two seasons. The introgression libraries were genotyped using the 35K Axiom® Wheat Breeder's Array and genetic diversity and population structure were examined. Significant phenotypic variation was observed across genotypes, treatments, and their interactions across seasons for all the 22 traits measured. Significant positive correlations were observed among grain yield and yield-attributing traits and root traits. Across seasons, a total of 233 marker-trait associations (MTAs) associated with fifteen traits of interest at different levels of nitrogen (N0, N60, and N120) were detected using 9,474 genome-wide single nucleotide polymorphism (SNP) markers. Of these, 45 MTAs for 10 traits in the N0 treatment, 100 MTAs for 11 traits in the N60 treatment, and 88 MTAs for 11 traits in the N120 treatment were detected. We identified putative candidate genes underlying the significant MTAs which were associated directly or indirectly with various biological processes, cellular component organization, and molecular functions involving improved plant growth and grain yield. In addition, the top 10 lines based on N response and grain yield across seasons and treatments were identified. The identification and introgression of superior alleles/donors improving the NUE while maintaining grain yield may open new avenues in designing next generation nitrogen-efficient high-yielding wheat varieties. [ABSTRACT FROM AUTHOR]

Background: Excessive application of nitrogen (N) fertilizer in cereal crops not only decreases the N use efficiency but also accelerates greenhouse gas (GHG) emission. Aim: To improve N use efficiency in wheat (Triticum aestivum L.) using precision N management and coating seeds with arbuscular mycorrhizal fungi (AMF). Methods: Field experiment laid out in split‐plot design was conducted to study the role of AMF consortia (four species) seed coating and different precision N management strategies in rationalizing fertilizer N use. Results: The AMF seed coating improved mycorrhization but did not improve N assimilation, grain yield, root weight, N uptake, chlorophyll value, normalized difference vegetative index, and physiological efficiency (PEN) of applied N fertilizer. The benefits of AMF seed coating in improving N assimilation were not visible even in no‐N treatment. Precision N management using leaf color chart (LCC), chlorophyll meter (SPAD), and GreenSeeker optical sensor (GS) sustained wheat grain yield equivalent to the soil‐test based N fertilizer recommendation with the average savings of 20% N fertilizer. Precision N management strategies improved mean recovery efficiency (REN) and partial factor productivity (PFPN) of applied N fertilizer, respectively by 26.0% and 26.4% over the soil‐test based N management. Spectral properties measured with LCC, SPAD and GS showed good correlation (R2 > 0.71) with grain yield, depicting great potential of optical sensing tools in predicting grain yield and inferring need‐based fertilizer N topdressings decisions in wheat. Conclusions: Precision N management provides a potential solution to improve N nutrition in wheat while reducing nitrous oxide (N2O) and total GHG emissions by 23.2 and 23.6%, respectively, in comparison to soil‐test based N application. [ABSTRACT FROM AUTHOR]

Three-year multi-location field experiments were conducted in soils of varying inherent nitrogen (N) supply in diverse agro-climatic zones for improving productivity and mitigating N2O emissions in timely sown and late sown wheat. The biomass, total N uptake (TNU) and spectral properties were monitored at different growth stages. Biomass production and TNU statistics of only 0.76% and 3.4%, respectively, till Zadoks 14 growth stage (four leaves stage) revealed that applying all fertilizer N dose by Zadoks 14 is not an appropriate strategy to assure fertilizer N supply throughout the growth stages. Rescheduled fertilizer N topdressings with moderate N (25 kg ha−1) at sowing and remaining N dose in two equal splits at Zadoks 14 and Zadoks 29 (main shoot and 9 more tillers) growth stages reduced N2O and GHG emissions, respectively, by 32.4% and 30.6%. Sustained N supply till grain filling produced an average of 5.1% to 10.5% higher grain yield and 2.1% to 10.5% higher grain protein content. The spectral properties recorded with PAU-LCC and SPAD meter at Zadoks 29 growth stage governed the grain yield response to fertilizer N application and can be used to fine-tune fertilizer N topdressing decisions over a wide range of varieties, locations, sowing timings and environments. [ABSTRACT FROM AUTHOR]

A 5-year field study was conducted to improve nitrogen (N) and phosphorus (P) use efficiencies in wheat with the synergistic use of plant growth-promoting rhizobacteria (PGPR), arbuscular mycorrhizal fungi (AMF), and spectral properties for deriving need-based fertilizer N management decisions. Bio-fertilizer consortium inoculation on wheat seed improved rhizosphere mycorrhization, albeit native mycorrhiza also produced mycorrhiza colonization. Lower mycorrhiza colonization was observed in no-P and high P treatments at 30 and 60 days after sowing (DAS) when wheat seeds were not inoculated with bio-fertilizer. However, the mycorrhiza colonization was independent of the fertilizer P level at 60 DAS in the inoculated treatments. The integrated nutrient management with bio-fertilizer and need-based N use sustained highest grain yield with 16.7% and 25% less use of fertilizer N and P, respectively. The agronomic (AE) and recovery efficiencies (RE) of applied N and P were increased by 23.0% (AEN), 21.3% (REN), 40.2% (AEP) and 49.8% (REP), respectively. On-farm validation studies exhibited improvement in partial factor productivity of fertilizer P (PFPP) by 35.8% and fertilizer N (PFPN) by 22.5% in comparison with the soil test-based recommendation. The synergistic use of bio-fertilizer and need-based N management improved the PGPR population, dehydrogenase and alkaline phosphatase activities in soil. The improved soil microbiological properties attributed to better mycorrhization and microflora propagation in soil-facilitated nutrient assimilation and thus higher N and P use efficiencies in wheat. [ABSTRACT FROM AUTHOR]

Abstract: Over and untimely application of fertilizer nitrogen (N) are the major constrains in improving fertilizer N recovery efficiency in irrigated wheat (Triticum aestivum L.). Large field to field and seasonal variability further lower fertilizer N recovery efficiency when broad based blanket recommendations are followed. Six field experiments were conducted during 2005 to 2009 at different locations to establish threshold leaf colour greenness to guide in-season need-based fertilizer N topdressings in wheat. Colour of the first top fully exposed leaf as measured by comparison with different shades of green colour on a leaf colour chart (LCC) and wheat grain yield were significantly correlated. The Cate-Nelson plot of leaf greenness expressed as LCC values against relative grain yield of 0.91 indicated that leaf greenness between LCC shade 4 and 5 may guide crop demand driven N applications in wheat. A series of experiments with progressive refinement in treatments were conducted to develop adequate need-based N management strategy using a single threshold LCC value in irrigated wheat. It was found that a dose of at least 25kgNha−1 should be applied at planting. At 1st irrigation (crown root initiation) stage leaf greenness cannot be quantified properly using LCC due to small leaf size and thus it did not lead to adequate fertilizer N management decision. At 2nd irrigation (maximum tillering) stage leaf colour of the first fully exposed leaf served as best indicator of inherent soil N supply as well as crop N needs and thus helped guide need-based fertilizer N top dressing for improving fertilizer N use efficiency in wheat. Fertilizer N management strategy based on application of prescriptive doses of 25kgNha−1 at planting and 45kgNha−1 at 1st irrigation and then a dose of 30 or 45kgNha−1 at 2nd irrigation stage depending on colour of the leaf to be ≥LCC 4 or

Blanket fertilizer nitrogen (N) recommendations for large irrigated wheat tracts lead to low N-use efficiency due to field-to-field variability in soil N supply and seasonal variability in yield. To achieve high N use efficiency, a site-specific N management strategy using GreenSeeker™ optical sensor was evaluated. We conducted seven field experiments during 2004-2006 at three locations to define relationships between in-season sensor measurements and yield of wheat and to know whether response of wheat to fertilizer N can be estimated by sensor measurements. During 2005-2007, four field experiments were conducted to assess the sensor-based N management strategy and to work out prescriptive N management to be followed prior to applying sensor-guided fertilizer dose. We observed robust relationships between in-season sensor-based estimates of yield at Feekes 5-6 and 7-8 stages and actual wheat yields. Response of wheat to fertilizer N defined by the sensor was highly correlated with harvest response index. Sensor-guided fertilizer N applications resulted in high yield levels and high N-use efficiency. Application of 90 kg N ha at planting or in two equal doses at planting and crown root initiation stage was the appropriate prescriptive fertilizer N management. This study reveals that high N-use efficiency in irrigated wheat can be achieved by replacing blanket fertilizer recommendation by an optical sensor-based N management strategy consisting of applying moderate amount of fertilizer N at planting and crown root initiation stages and sensor-guided fertilizer N dose at Feekes 5-6 or 7-8 stages of wheat. [ABSTRACT FROM AUTHOR]

Abstract  Poultry litter (PL) is an important nutrient source; however, no information is available regarding its value in supplying N and P in rice–wheat (RW) production. A three-year field study was conducted at Ludhiana, Punjab, India on a loamy sand soil to identify optimum combination of PL and N and P fertilizers for a sustainable RW production. The litter was applied to rice at 5 Mg ha−1 as a single application and supplemented with different rates of N. The residual effect of PL and the direct effects of the different combinations of N and P were studied in the following wheat. Nitrogen and P mineralization from PL was studied under controlled conditions in the laboratory, and macronutrient input–output balances were estimated from field results. About 46% of the N from PL was released after 60 days of incubation. The release of P from the PL occurred mainly during the initial 20 days after incubation, accounting for 15–17% of the total P. Combining PL with fertilizer N (40 kg ha−1) increased rice yield and nutrient uptake similar to what was obtained with the application of recommended fertilizer N (120 kg ha−1). In the following wheat, the residual effect of PL was equal to 30 kg N ha−1 and 13 kg P ha−1. After three annual cropping cycles and PL application, mean soil organic C increased by 17%, Olsen-P by 73%, and NH4OAc-extractable-K by 24%. Most treatments had positive P but negative K balances. About 11% of the net P balance was recovered from the soil as Olsen-P. The study showed that optimum N and P fertilizer doses for an RW system receiving 5 Mg ha−1 of PL are 40 kg N ha−1 for rice and 90 kg N + 13 kg P ha−1 for the following wheat. Safe and effective management of PL should be based on P balance, particularly when regular applications of PL are to be made in the RW system. [ABSTRACT FROM AUTHOR]

Increasing nitrogen fertilizer applications have sustained a growing world population in the 20th century. However, to avoid any further associated environmental damage, new sustainable agronomic practices together with new cultivars must be developed. To date the concept of nitrogen use efficiency (NUE) has been useful in quantifying the processes of nitrogen uptake and utilization, but we propose a shift in focus to consider nitrogen responsiveness as a more appropriate trait to select varieties with lower nitrogen requirements. We provide a roadmap to integrate the regulation of nitrogen uptake and assimilation into varietal selection and crop breeding programs. The overall goal is to reduce nitrogen inputs by farmers growing crops in contrasting cropping systems around the world, while sustaining yields and reducing greenhouse gas (GHG) emissions. Current practice for managing nitrogen (N) use for cereal production are not environmentally sustainable. Overuse of N fertilizers is a global problem for millions of farmers who must decide on N applications whether, when and how much. A combination of improved advice on N management for specific cropping regimes is required, together with a breeding target of new commercial crop varieties with sustainable yields and a low N requirement. While N use efficiency (NUE) has been a useful concept for quantifying the genetic differences in N uptake and utilization, the concept of an economic N optimum derived from N yield dose–response curves may provide new insights for lowering the N requirement. [ABSTRACT FROM AUTHOR]

Wheat is grown on more than 240 million hectares globally, more than any other commercial crop. Variation for nitrogen-use efficiency (NUE) in wheat germplasm is very important as efficiency of nitrogen fertilizers use can have significant effect on overall consumption of N. In the present study we used nested synthetic hexaploid wheat introgression libraries to detect genetic variation associated with NUE and related traits. The libraries were genotyped with 9474 SNP markers and used for genome-wide association mapping. Significant phenotypic variation was observed for all measured and derived traits. We detected 10 Quantitative trait locus (QTL) and 19 marker-trait associations (MTAs) possibly involved in improving NUE. Of these, 5 QTL and 8 MTAs detected under nitrogen-limited conditions have potential for use in breeding to increase nitrogen-deficiency tolerance. Nitrate transporter genes collocated with detected MTAs showed significant changes in expression of TaNRT2 genes in response to N-starvation and N-recovery. The identified promising breeding lines with stable yield, better NUE and acceptable protein content may constitute an important genetic resource in improving NUE of modern wheat varieties. • To meet future wheat production demands, improving nitrogen use while maintaining grain yield is vital. • We identified marker-trait associations improving nitrogen use efficiency while maintaining grain yield under varying nitrogen levels. • We also identified promising breeding lines with significant genetic variations and carrying the trait-associated markers or candidate genes. • These may serve as potential donors to be exploited further in genomics-assisted breeding programs targeting improved NUE while maintaining grain yield in wheat. [ABSTRACT FROM AUTHOR]

Abstract: Large quantities of rice husk ash (RHA), bagasse ash (BA) and coal fly ash (FA) are available in many Asian countries as waste materials, which create a serious disposal problem. Recycling of these ashes on agricultural land can help to improve physical and chemical fertility of soil. The present field experiment was conducted for three and half years to explore the possibilities to utilize these waste materials as soil amendments to improve productivity of rice–wheat system (RWS). The treatments consisted of application of RHA and BA at 10Mgha−1 to either wheat or to rice or to both wheat and rice and 20Mgha−1 to rice alone. The rates used for FA were 15 and 30Mgha−1. Addition of RHA and BA significantly increased the grain yield of wheat and rice but FA caused small increases in crop yields. Direct application of RHA and BA to wheat was significantly superior than their application to rice in the RWS. Direct application of RHA and BA to wheat resulted in 25 and 24% increase in mean grain yield of wheat and 10 and 11% increase in subsequent rice crop, respectively. However, direct application to rice resulted in 8 and 11% yield increase in rice and 10 and 14% increase in subsequent wheat for RHA and BA, respectively. Application of RHA and BA at 20Mgha−1 to rice resulted in lower RWS productivity than that applied at 10Mgha−1 to wheat. There was no significant effect of these ashes on heavy metal contents in grain and straw of the 7th crop of wheat. Application of three types of ashes generally resulted in positive P balance in RWS, however, K balance remained negative. These results suggest that RHA and BA can be recycled successfully in rice–wheat system to improve its productivity with no adverse effect on soil health. [Copyright &y& Elsevier]