Rice N Use Efficiency Research Articles

Blended controlled-release nitrogen fertilizer increases rice post-anthesis nitrogen accumulation, translocation and nitrogen-use efficiency.

One-time application of blended controlled-release nitrogen fertilizer (CRN) has the potential to solve the difficulty of top-dressing fertilizer in the cultivation of rice and reduce the cost of CRN fertilizer application. However, its effects on rice dry matter and nitrogen (N) accumulation and translocation, yield and N-use efficiency (NUE) remain uncertain. Field experiments were carried out at three sites (Mingguang, Chaohu, and Guichi) in the Yangtze River Delta in China to compare the effects of the conventional split applications of urea and the blended CRN and on post-anthesis dry matter and N accumulation and translocation, yield, and NUE in rice at 0, 60, 120, 180, and 240kg N ha-1. The results showed that at the equal N application rates, compared under the conventional N fertilizer treatment, the blended CRN application significantly increased the rice yield by an average of 0.9-6.9%, mainly due to increase the number of spikelets per panicle. The highest yield achieved with blended CRN treatment occurred at 200kg N ha-1, with an NUE of 45.9%. Moreover, in comparison to the conventional N fertilizer, the blended CRN treatment increased pre-anthesis N translocation (Pre-NT) by 1.0-19.8%, and the contribution of pre-NT to grain N by 0.2-8.7%, and NUE by 3.2-28.4%. Meanwhile, the blended CRN treatment reduced labor costs by 1800 Yuan ha-1 and enhanced the economic gains by 21.5-68.8%. Therefore, one-time application of blended CRN ≤ 200kg N ha-1 application rate improved rice yield, NUE, and economic profit compared to equivalent rates of split applied conventional N fertilizers.

Nitrate-responsive transcriptome analysis of rice RGA1 mutant reveals the role of G-proteinalpha subunit in negative regulation of nitrogen-sensitivity and use efficiency.

Nitrate-responsive transcriptomic, phenotypic and physiological analyses of rice RGA1mutant revealed many novel RGA1-regulated genes/processes/traits related to nitrogen use efficiency, and provided robust genetic evidence of RGA1-regulation of NUE. Nitrogen (N) use efficiency (NUE) is important for sustainable agriculture. G-protein signalling was implicated in N-response/NUE in rice, but needed firm genetic characterization of the role of alpha subunit (RGA1). The knock-out mutant of RGA1 in japonica rice exhibited lesser nitrate-dose sensitivity than thewild type (WT), in yield and NUE. We, therefore, investigated its genomewide nitrate-response relative to WT. It revealed 3416 differentially expressed genes (DEGs), including 719 associated with development, grain yield and phenotypic traits for NUE. The upregulated DEGs were related to photosynthesis, chlorophyll, tetrapyrrole and porphyrin biosynthesis, while the downregulated DEGs belonged to cellular protein metabolism and transport, small GTPase signalling, cell redox homeostasis, etc. We validated 26 nitrate-responsive DEGs across functional categories by RT-qPCR. Physiological validation of nitrate-response in the mutant and theWT at 1.5 and 15mM doses revealed higher chlorophyll and stomatal length but decreased stomatal density, conductance and transpiration. The consequent increase in photosynthesis and water use efficiency may have contributed to better yield and NUE in the mutant, whereas the WT was N-dose sensitive. The mutant was not as N-dose-responsive as theWT in shoot/root growth, productive tillers and heading date, but equally responsive as WT in total N and protein content. The RGA1 mutant was less impacted by higher N-dose or salt stress in terms of yield, protein content, photosynthetic performance, relative water content, water use efficiency and catalase activity. PPI network analyses revealed known NUE-related proteins as RGA1 interactors. Therefore, RGA1 negatively regulates N-dose sensitivity and NUE in rice.

OsNPF3.1, a member of the NRT1/PTR family, increases nitrogen use efficiency and biomass production in rice

The overuse of nitrogen (N) fertilizer in fields has increased production costs and raised environmental concerns. Increasing the N use efficiency (NUE) of rice varieties is crucial for sustainable agriculture. Here we report the cloning and characterization of OsNPF3.1, a gene that controls rice NUE. An amino acid mutation in the OsNPF3.1 coding region caused different NUEs in wild and cultivated rice. OsNPF3.1, which is expressed mainly in the aerial parts of rice, also affects rice plant height, heading date, and thousand-grain weight. The OsNPF3.1 protein is located in the plasma membrane. When OsNPF3.1 was subjected to artificial selection, two naturally varying loci were associated with NUE, of which OsNPF3.1Chr6_8741040 differed between indica and japonica rice. OsNPF3.1 can be used as a new target gene for breeding rice varieties with high NUE.

Improved nitrogen use efficiency, carbon sequestration and reduced environmental contamination under a gradient of manure application

The challenge of reducing the environmental contamination related to agricultural practices to improve nitrogen (N) use efficiency (NUE), carbon (C) sequestration, and crop yield, requires efficient N fertilization and management strategies. We carried out a field experiment from 2016 to 2018 exploring the effect of the gradual replacement of mineral N with organic manure N on soil properties, soil organic C storage, soil total N storage, rice grain yield and yield components, N uptake and C accumulation of rice, and NUE. Moreover, we explained the relationship among the proportions of manure added to fertilizers, soil properties, rice grain yield and yield components, and aboveground N uptake and C accumulation of rice after harvest. Compared to mineral fertilization, 50% manure improved NUE and increased the effective panicle, seed setting rate, grain yield, and straw yield. However, in comparison to mineral fertilization, 100% manure decreased the effective panicle, the number of spikelets per panicle, grain yield, and straw yield and decreased partial factor productivity (PFP), N agronomic efficiency (AEN), and N recovery efficiency (REN). Moreover, in comparison with mineral fertilization, 50% manure increased the aboveground N uptake and C accumulation of rice, decreased the N surplus by 61.5%, and increased the apparent accumulated N recovery efficiency by 10.7%. In comparison to mineral fertilization, manure percentages exceeding 25% increased the total and available N, phosphorus, potassium, and organic C contents in soil. According to redundancy analysis, aboveground C accumulation and N uptake of rice jointly contributed to the variation in grain yields and yield components by 27.9%. In conclusion, 50% manure is a promising ecologically friendly strategy that improves the grain yield, N uptake, C sequestration, and NUE of rice and improves soil fertility. Simultaneously, 50% manure decreases the risk of environmental contamination.

Rice NIN-LIKE PROTEIN 3 modulates nitrogen use efficiency and grain yield under nitrate-sufficient conditions.

Nitrogen (N) is an essential macronutrient for crop growth and yield. Improving the N use efficiency (NUE) of crops is important to agriculture. However, the molecular mechanisms underlying NUE regulation remain largely elusive. Here we report that the OsNLP3 (NIN-like protein 3) regulates NUE and grain yield in rice under N sufficient conditions. OsNLP3 transcript level is significantly induced by N starvation and its protein nucleocytosolic shuttling is specifically regulated by nitrate. Loss-of-function of OsNLP3 reduces plant growth, grain yield, and NUE under sufficient nitrate conditions, whereas under low nitrate or different ammonium conditions, osnlp3 mutants show no clear difference from the wild type. Importantly, under sufficient N conditions in the field, OsNLP3 overexpression lines display improved grain yield and NUE compared with the wild type. OsNLP3 orchestrates the expression of multiple N uptake and assimilation genes by directly binding to the nitrate-responsive cis-elements in their promoters. Overall, our study demonstrates that OsNLP3, together with OsNLP1 and OsNLP4, plays overlapping and differential roles in N acquisition and NUE, and modulates NUE and the grain yield increase promoted by N fertilizer. Therefore, OsNLP3 is a promising candidate gene for the genetic improvement of grain yield and NUE in rice.

Meta-QTLs linked to nitrogen use efficiency are randomly distributed in Indian rice germplasm

Nitrogen (N) recognized as a critical element for plant growth plays a fundamental role in rice cultivation. The N use efficiency (NUE) hovers around 30-35% in rice, suggesting a significant loss of N from the rice fields. Improving the NUE therefore would require genetic interventions and breeding. The cultivar improvement for N uptake and utilization is required to elevate NUE to further heights. Several quantitative trait loci (QTLs) for NUE under varying conditions and genetic backgrounds have been reported in rice. Consolidation of this distributed and unorganized information is necessary to identify critical genomic regions to be used for crop improvement. Therefore, a Meta-analysis from an assembly of 506 QTLs reported from 18 different studies was performed to identify the most significant genomic regions associated with NUE in rice. A total of 12 meta-QTLs (mQTLs) related to the traits such as NUE and grain yield per plant under N deficit conditions have been identified over four rice chromosomes namely 1, 3, 4, and 8. Evaluation of these mQTLs in a set of Indian rice germplasm revealed a significant association of the meta loci with N use parameters and showed wide distribution in the germplasm. Identification of mQTLs on different chromosomes together with their respective markers will help recruit them in marker-assisted selection (MAS) to develop N use efficient genotypes.

Nitrogen-fixing cyanobacteria have the potential to improve nitrogen use efficiency through the reduction of ammonia volatilization in red soil paddy fields

Nitrogen-fixing cyanobacteria (NFC) biofertilizers have demonstrated great potential in improving rice yield and soil fertility. However, few studies have systematically evaluated the effects of combined application of NFC biofertilizers and chemical nitrogen (N) fertilizer on ammonia (NH3) volatilization and rice N absorption in red soil paddy fields. Therefore, we conducted a 2-year single cropping paddy field study to determine the NH3 volatilization loss from paddy soil, as well as rice yield and N use efficiency (NUE). The experiment designed five treatments, including one control (CK, no N applied) and four experimental treatments (N100, complete application of chemical N fertilization; RN50, replacing half of chemical N fertilizer with NFC; RN100, complete replacement of chemical N fertilizer with NFC; N50, only half application of chemical N fertilizer) based on different chemical N fertilizer and NFC biofertilizers application ratios. The results showed that the average cumulative NH3 volatilization losses of RN50 and N50 treatments were reduced by 41.63% and 45.34% than that of N100 treatment, respectively, mainly due to the reduction of ammonium N content in the overlying water and topsoil. The average NUE of RN50 and N50 treatments were 57.85% and 48.49%, which were 43.83% and 20.56% higher than that of N100, respectively. Path analysis results showed that the application of NFC increased the total soil N content and mitigated the volatilization of NH3, which increased the residence time of N in the paddy field, thereby increasing the NUE of rice. The average rice yield of RN50 was 5603.85 kg ha−1, which was not significantly different from N100, but 18.62% higher than N50. Although RN100 elevated NUE and reduced NH3 volatilization, its grain yield was significantly lower than that of N100. These results suggest that the replacement of an appropriate proportion of chemical N fertilizer with NFC could be a promising approach to mitigating NH3 volatilization, enhancing rice NUE, and maintaining rice yield in red soil paddy fields.

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.

Candidate Gene Analysis for Nitrogen Absorption and Utilization in Japonica Rice at the Seedling Stage Based on a Genome-Wide Association Study.

Over-application of nitrogen (N) fertilizer in fields has had a negative impact on both environment and human health. Domesticated rice varieties with high N use efficiency (NUE) reduce fertilizer requirements, enabling sustainable agriculture. Genome-wide association study (GWAS) analysis of N absorption and utilization traits under low and high N conditions was performed to obtain 12 quantitative trait loci (QTLs) based on genotypic data including 151,202 single-nucleotide polymorphisms (SNPs) developed by re-sequencing 267 japonica rice varieties. Eighteen candidate genes were obtained by integrating GWAS and transcriptome analyses; among them, the functions of OsNRT2.4, OsAMT1.2, and OsAlaAT genes in N transport and assimilation have been identified, and OsJAZ12 and OsJAZ13 also play important roles in rice adaptation to abiotic stresses. A NUE-related candidate gene, OsNAC68, was identified by quantitative real-time PCR (qRT-PCR) analyses. OsNAC68 encodes a NAC transcription factor and has been shown to be a positive regulator of the drought stress response in rice. Overexpression of OsNAC68 significantly increased rice NUE and grain yield under deficient N conditions, but the difference was not significant under sufficient N conditions. NUE and grain yield significantly decreased under both N supply conditions in the osbnac68 mutant. This study provides crucial insights into the genetic basis of N absorption and utilization in rice, and a NUE-related gene, OsNAC68, was cloned to provide important resources for rice breeding with high NUE and grain yield.

Nitrogen management practices for improving yield and nitrogen use efficiency in rice (Oryza sativa)

A field experiment was conducted on rice (Oryza sativa L.) during kharif season of 2017 at Crop Research Centre of Sardar Vallabhbhai Patel University of Agriculture and Technology, Meerut (U P) to assess the nitrogen (N) use efficiency and performance of rice under different nitrogen management practice. Management practices included N levels with modified application through leaf colour chart (LCC) and chlorophyll meter (SPAD). The study shows that treatment T6 (LCC (50 kg N/ha) with basal N @50 kg/ha)gave highest yield and N-use efficiency which were comparable to T9 (SPAD (67 kg N/ha) with basal N @33 kg/ha). The total biological yield (grain + straw) of rice was significantly higher in T6 (114.4 q/ha) as compared to control (66.9 q/ha). The SPAD and LCC-treated plot showed higher N-use efficiency in rice over fixed-scheduling N treatments. Highest N content(1.88% (grain) and 0.76% (straw)) and uptake (128.14 kg/ha) was recorded in T6 treatmentin all stages (tillering, PI and harvest) which was comparable with T8 and T9 treatment.

Rice NIN-LIKE PROTEIN 4 plays a pivotal role in nitrogen use efficiency.

SummaryNitrogen (N) is one of the key essential macronutrients that affects rice growth and yield. Inorganic N fertilizers are excessively used to boost yield and generate serious collateral environmental pollution. Therefore, improving crop N use efficiency (NUE) is highly desirable and has been a major endeavour in crop improvement. However, only a few regulators have been identified that can be used to improve NUE in rice to date. Here we show that the rice NIN‐like protein 4 (OsNLP4) significantly improves the rice NUE and yield. Field trials consistently showed that loss‐of‐OsNLP4 dramatically reduced yield and NUE compared with wild type under different N regimes. In contrast, the OsNLP4 overexpression lines remarkably increased yield by 30% and NUE by 47% under moderate N level compared with wild type. Transcriptomic analyses revealed that OsNLP4 orchestrates the expression of a majority of known N uptake, assimilation and signalling genes by directly binding to the nitrate‐responsive cis‐element in their promoters to regulate their expression. Moreover, overexpression of OsNLP4 can recover the phenotype of Arabidopsis nlp7 mutant and enhance its biomass. Our results demonstrate that OsNLP4 plays a pivotal role in rice NUE and sheds light on crop NUE improvement.

Influence of Biochar on Nitrogen Use Efficiency and Root Morphology of Rice-Seedling in Two Contrasting Paddy Soils

Biochar may affect the root morphology and nitrogen (N) use efficiency (NUE) of rice at seedling stage, which has not been clearly verified until now. To clarify it, we conducted a pot experiment regarding to two soil types (Hydragric Anthrosol and Haplic Acrisol), two biochar application rates (0.5 wt% and 1.5 wt %) and two rice varieties (common rice var. Xiushui134 and hybrid super rice var. Zhongkejiayou12-6) meanwhile. Seedling NUE of common rice Xiuhui134 was significantly increased (p < 0.05) by 78.2% in Hydragric Anthrosol and by 91.4% in Haplic Acrisol following biochar addition with 1.5 wt%. However, biochar addition exerted no influence on seedling NUE of super rice Zhongkejiayou12-6 in both soils. Overall, 0.09–0.10 units higher soil pH and 105– 116% higher soil NH4+ -N were observed in Xiushui134 growing two soils with 1.5 wt% biochar. In addition, improved root morphology (including longer root length, larger root surface area, bigger root volume, and more root tips) contributed to the higher seedling NUE of Xiushui134 in two soils. The soil pH and NH4+ -N content, also the root morphology were influenced by biochar, which though could not thoroughly explained the NUE of Zhongkejiayou12-6. In conclusion, biochar application to paddy soil changed soil pH and NH4+ -N content, root growth, and the consequent seedling NUE of rice, which effects are relative with rice cultivar, biochar addition rate, and soil type.

Improving nitrogen and water use efficiencies of hybrid rice through methodical nitrogen–water distribution management

Methodical nitrogen–water (N–W) distribution management (MNWD) is a comprehensive N–W management technique designed to meet the requirements of rice production in China and specifically, the stabilization of grain yield and reduction of input resources. In this study, four split plot field experiments were conducted in two locations to examine the impact of MNWD on N use efficiency (NUE) and water use efficiency (WUE). We used high N efficiency rice varieties, Dexiang 4103 and Fyou 498, and low N efficiency varieties, Yixiang 3724 and Chuanyou 6203, and three N–W management techniques were established as subplot treatments, including farmers’ usual management (FU), N–W coupling management (NWC), and MNWD. Under MNWD, N application rates were 20% lower than those under NWC and FU, whereas the amounts of irrigation water were reduced by 20%–25% and 42%–48%, respectively. Yields under MNWD were similar to those under NWC (–2.51–0.45%), and there was an average yield increase of 8.13%–13.95% over FU. Rice plants under MNWD had larger amounts of roots, particularly in soil depth > 10 cm There were significant positive correlations between root dry mass in the various soil depths and WUE and irrigation WUE (IWUE), with the impact of roots in soil depth > 10 cm on rice plant WUE (IWUE) pronounced. MNWD’s IWUE was higher than that of NWC and FU by 22.95%–38.79% and 86.49%–126.69%, respectively, and its WUE was higher by 6.75%–20.74% and 37.05%–71.80%, respectively. Correlation analysis showed that the N absorption and accumulation capacities of rice plants under MNWD increased along with increases in soil fertility. The MNWD’s NUE advantage was apparent in soil depth > 10 cm where its root dry mass was especially large, with an average biomass productivity of N higher than that of NWC and FU by 4.16%–10.78% and 7.49%–18.01%, respectively and an N internal efficiency higher by 0.33%–8.29% and 5.32%–10.04%, respectively. Overall, MNWD effectively improved WUE and NUE of rice without significant grain yield reduction.

English

The use of green manures (GMs) in combination with nitrogen (N) fertilizer application is a promising practice to improve N fertilizer management in agricultural production systems. The main objective of this study was to evaluate the N use efficiency (NUE) of rice plant, derived from GMs including sunn hemp (Crotalaria juncea L.), millet (Pennisetum glaucum L.) and urea in the greenhouse. The experimental treatments included two GMs (sunn hemp-15N and millet-15N), absence of N organic source (without GM residues in soil) and four N rates, as urea-15N (0, 28.6, 57.2 and 85.8 mg N kg-1). The results showed that both rice grain and straw biomass yields under sunn hemp were greater than that of millet or without the application of GM. The NUE of rice under sunn hemp was greater than that under millet (18.9 and 7.8% under sunn hemp and millet, respectively). The urea N application rates did not affect the fertilizer NUE by rice (53.7%) with or without GMs. The NUE of GMs by rice plants ranged from 14.1% and 16.8% for root and shoot, respectively. The study showed that green manures can play an important role in enhancing soil fertility and N supply to subsequent crops. Key words: Oryza sativa L., sunn hemp, millet, isotopic diluition, nitrogen mineralization.

Identification of regulatory genes to improve nitrogen use efficiency

Guevara, D. R., Bi, Y.-M. and Rothstein, S. J. 2014. Identification of regulatory genes to improve nitrogen use efficiency. Can. J. Plant Sci. 94: 1009–1012. Crop production on soils containing sub-optimal levels of nitrogen (N) severely compromises yield potential. The development of crop varieties displaying high N use efficiency (NUE) is necessary in order to optimize N fertilizer use, and reduce the environmental damage caused by the current excessive application of N in agricultural areas. Genome-wide microarray analysis of rice plants grown under N-limiting environments was performed to identify NUE candidate genes. An early nodulin gene, OsENOD93-1, was strongly up-regulated during plant growth under low N. A constitutive Ubiquitin promoter was used to drive the expression of the OsENOD93-1 gene in transgenic plants to determine the importance of OsENOD93-1 for rice NUE. Transgenic rice plants over-expressing the OsENOD93-1 gene achieved ∼23% and 16% more yield and biomass, respectively, compared with wild-type plants when grown under N-limitation conditions. OsENOD93-1-OX transgenic plants accumulated a higher amount of total amino acids in the roots and xylem sap under N stress, suggesting that OsENOD93-1 plays a role in the transportation of amino acids. Taken together, we demonstrate that an effective way to identify NUE gene candidates involves both transcriptional profiling coupled with a transgenic validation approach to improve complex traits such as NUE in important crops.

Identification of regulatory genes to improve nitrogen use efficiency

Guevara, D. R., Bi, Y.-M. and Rothstein, S. J. 2014. Identification of regulatory genes to improve nitrogen use efficiency. Can. J. Plant Sci. 94: 1009-1012. Crop production on soils containing sub-optimal levels of nitrogen (N) severely compromises yield potential. The development of crop varieties displaying high N use efficiency (NUE) is necessary in order to optimize N fertilizer use, and reduce the environmental damage caused by the current excessive application of N in agricultural areas. Genome-wide microarray analysis of rice plants grown under N-limiting environments was performed to identify NUE candidate genes. An early nodulin gene, OsENOD93-1, was strongly up-regulated during plant growth under low N. A constitutive Ubiquitin promoter was used to drive the expression of the OsENOD93-1 gene in transgenic plants to determine the importance of OsENOD93-1 for rice NUE. Transgenic rice plants over-expressing the OsENOD93-1 gene achieved ~23% and 16% more yield and biomass, respectively, compared w...

Differential responses of system of rice intensification (SRI) and conventional flooded-rice management methods to applications of nitrogen fertilizer

Rising food demand, slowing productivity growth, poor N-use efficiency in rice, and environmental degradation necessitate the development of more productive, environmentally-sound crop and soil management practices. The system of rice intensification (SRI) has been proposed as a methodology to address these trends. However, it is not known how its modified crop-soil-water management practices affect efficiency of inorganic nitrogen applications. Field experiments investigated the impacts of SRI management practices with different N-application rates on grain yield, root growth and activity, uptake of N and its use-efficiency, leaf chlorophyll content, leaf N-concentration, and photosynthetic rate in comparison with standard management practices for transplanted flooded rice (TFR). Overall, grain yield with SRI was 49 % higher than with TFR, with yield enhanced at every N application dose. N-uptake, use-efficiency, and partial factor productivity from applied N were significantly higher in SRI than TFR. Higher leaf nitrogen and chlorophyll contents during the ripening-stage in SRI plants reflected delayed leaf-senescence, extension of photosynthetic processes, and improved root-shoot activities contributing to increased grain yield. Rice grown under SRI management used N fertilizer more efficiently due to profuse root development and improved physiological performance resulting in enhanced grain yield compared to traditional flooded rice.

Crop demand-driven site-specific nitrogen applications in rice (Oryza sativa) and wheat (Triticum aestivum): some recent advances

Management of fertilizer nitrogen in rice (Oryza sativa L.) and wheat (Triticum aestivum L. emend. Fiori &amp; Paol.) in India typically consists of blanket recommendations, developed for large tracts having similar climate and land forms. It cannot help the increase N-use efficiency beyond a limit. Further improvement can be achieved only by planning strategies for fertilizer N management responsive to temporal variations in crop N demand and fieldiito- field variability in soil-N supply. Improvement in the synchrony between crop N demand and the N supply from soil or the applied N fertilizer is likely to be the most promising strategy to improve N-use efficiency. It can be achieved by following real-time N management based on periodic assessment of plant-N status and delayed application of fertilizer N until the N level goes below a critical level. Gadgets like chlorophyll-meter (SPAD-meter) and inexpen- sive leaf colour chart (LCC) have proved quick and reliable tools to decide the time when fertilizer N needs to be applied to the crop. Recently significant progress has been made in the development and on-farm evaluation of LCC-based real-time N management in rice, but there is a need to work out appropriate criteria for using need- based N-management strategy in wheat. Optical sensors offer an opportunity to take into account both plant N sta- tus (or leaf colour) as well as crop biomass for making crop-demand-driven fertilizer-N recommendations. Combi- nation of preventive location-specific split schedule with corrective LCC or SDAD-meter or optical sensor-based N management constitutes another attractive strategy for achieving high N-use efficiency in rice and wheat. The fixed-time or adjustable-dose approach seems very promising for wheat, because unlike in rice, the fertilizer appli- cations need to be synchronized with irrigation events. Appropriate preventive fertilizer-N management scenarios need to be worked out that can be used before using the SPAD meter, LCC or optical sensors to guide corrective fertilizer-N application at a given crop-growth stage.