Improving Crop Nitrogen Research Articles

Is auxin the key to improve crop nitrogen use efficiency for greener agriculture?

Strengthening future food security through the application of unsustainable levels of inorganic nitrogen (N) fertilizers to crop fields may exacerbate environmental damage. Coordination of N-use efficiency (NUE) and plant growth is, therefore, crucial for sustainable agriculture. Auxin plays pivotal roles in developmental and signaling responses that affect NUE. Hence, a better understanding of these processes provides great potential to improve crop NUE. This review summarizes the effects of auxin on N-related and root developmental processes that either directly or indirectly affect NUE in the model plant Arabidopsis and major crop species to highlight the potential of fostering sustainable agricultural development in the future through modulating auxin-related processes.

Drive soil nitrogen transformation and improve crop nitrogen absorption and utilization - a review of green manure applications.

Green manure application presents a valuable strategy for enhancing soil fertility and promoting ecological sustainability. By leveraging green manures for effective nitrogen management in agricultural fields can significantly reduce the dependency of primary crops on chemical nitrogen fertilizers, thereby fostering resource efficiency. This review examines the current advancements in the green manure industry, focusing on the modulation of nitrogen transformation in soil and how crops absorb and utilize nitrogen after green manure application. Initially, the influence of green manure on soil nitrogen transformation is delineated, covering processes such as soil nitrogen immobilization, and mineralization, and losses including NH3, N2O, and NO3 --N leaching. The review then delves into the effects of green manure on the composition and function of soil microbial communities, highlighting their role in nitrogen transformation. It emphasizes the available nitrogen content in the soil, this article discussing nitrogen uptake and utilization by plants, including aspects such as nitrogen translocation, distribution, the root system, and the rhizosphere environment of primary crops. This provides insights into the mechanisms that enhance nitrogen uptake and utilization when green manures are reintroduced into fields. Finally, the review anticipates future research directions in modulating soil nitrogen dynamics and crop nitrogen uptake through green manure application, aiming to advance research and the development of the green manure sector.

Optimizing Nitrogen Sources in Top Dressing for Wheat: Field Study on Growth, Yield, and Ammonia Volatilization.

In alkaline calcareous soils, ammonia volatilization is the primary nitrogen (N) loss process, resulting in the reduced N use efficiency of crops. This study aimed at assessing the impact of different N sources for top dressing on ammonia volatilization, as well as their effects on wheat growth and yield over two years. In each year, half of the recommended N was applied as a basal dose using diammonium phosphate (DAP) and urea. The remaining half was top-dressed 35 days after sowing with various sources: prilled urea (PU), granular urea (GU), ammonium sulfate (AS), and calcium ammonium nitrate (CAN) in the first year; PU, urea coated with a urease inhibitor from 20 g (VnU-20) and 40 g (VnU-40) leaves of Vachellia nilotica, biochar-coated urea (BU), and urease inhibitor paraphenylenediamine-coated urea (PPDU) in the second year. Ammonia volatilization losses were tracked for up to 12 weeks from sowing. Ammonia losses from basal-applied N remained consistent in both years, comprising around 4% of the applied N. In the first year, top-dressed AS resulted in the highest losses, followed by GU, while losses from urea and CAN were statistically similar. In the second year, coated fertilizers showed lower ammonia losses compared to PU, with VnU-40 displaying the least losses, 48% less than PU. Nitrogen concentration in wheat grain and straw exhibited a negative correlation with ammonia losses. The choice of top-dressed N source influenced tillering, biological, straw, and grain yields of wheat. In the first year, CAN provided maximum yield benefits, and in the second year, VnU-20 exhibited 27% more grain yield than PU. These findings suggest that top dressing with coated urea, especially VnU-20, has the potential to reduce ammonia losses, improve crop nitrogen status, and enhance economic yield compared to other nitrogen sources.

The NIN-LIKE PROTINE1 (CsNLP1) transcription factor is involved in modulating the nitrate response in cucumber seedlings

Cucumber is one of the important vegetables cultivated in facilities in China. Due to the deterioration of soil quality in facilities and the low nitrogen use efficiency of existing varieties, it is common to pursue high yield through excessive application of nitrogen fertilizer. Improving crop nitrogen use efficiency is one of the important means to reduce nitrogen fertilizer input. Previous studies have shown that NLP (NIN-like protein) transcription factor family play an important role as transcription factors in regulating plant physiological responses to external nitrogen changes. However, there are few reports on NLPs in cucumber. Here we report that CsNLP1 is a potential candidate to improve cucumber nitrogen use ability. CsNLP1 silencing lines by virus-induced gene silencing (VIGS) showed a significant decrease in the plant biomass, chlorophyll content, nitrogen uptake, total nitrogen content, activities of NR, NIR, GDH, GOGAT and GS, and expression levels of genes involved in nitrogen assimilation and signalling under different nitrogen concentrations. In addition, transfer of CsNLP1 into Arabidopsis nlp7-1 mutant found that the phenotype, nitrate (NO3-) content, NR activity, NIR activity, GDH activity, GOGAT activity and GS activity in transgenic lines could be restored to the wild type level after NO3- treatment. Further study found that CsNLP1 could regulate the expression of NO3- responsive genes such as AtNIR1, AtNIA2, AtNRT1.1 and AtGS2 in plants. Overall, our data indicated that CsNLP1 can affect plant growth, and regulate nitrate assimilation by regulating nitrogen-related genes.

Gene Expression, Enzyme Activity, Nitrogen Use Efficiency, and Yield of Rice Affected by Controlled-Release Nitrogen.

Controlled- or slow-release urea can improve crop nitrogen use efficiencies and yields in many agricultural production systems. The effect of controlled-release urea on the relationships between levels of gene expression and yields has not been adequately researched. We conducted a 2 year field study with direct-seeded rice, which included treatments of controlled-release urea at four rates (120, 180, 240, and 360 kg N ha-1), a standard urea treatment (360 kg N ha-1), and a control treatment without applied nitrogen. Controlled-release urea improved the inorganic nitrogen concentrations of root-zone soil and water, functional enzyme activities, protein contents, grain yields, and nitrogen use efficiencies. Controlled-release urea also improved the gene expressions of nitrate reductase [NAD(P)H] (EC 1.7.1.2), glutamine synthetase (EC 6.3.1.2), and glutamate synthase (EC 1.4.1.14). With the exception of glutamate synthase activity, there were significant correlations among these indices. The results showed that controlled-release urea improved the content of inorganic nitrogen within the rice root zone. Compared with urea, the average enzyme activity of controlled-release urea increased by 50-200%, and the relative gene expression was increased by 3-4 times on average. The added soil nitrogen increased the level of gene expression, allowing enhanced synthesis of enzymes and proteins for nitrogen absorption and use. Hence, controlled-release urea improved the nitrogen use efficiency and the grain yield of rice. Controlled-release urea is an ideal nitrogen fertilizer showing great potential for improving rice production.

Weighted gene co-expression network analysis of nitrogen (N)-responsive genes and the putative role of G-quadruplexes in N use efficiency (NUE) in rice.

Rice is an important target to improve crop nitrogen (N) use efficiency (NUE), and the identification and shortlisting of the candidate genes are still in progress. We analyzed data from 16 published N-responsive transcriptomes/microarrays to identify, eight datasets that contained the maximum number of 3020 common genes, referred to as N-responsive genes. These include different classes of transcription factors, transporters, miRNA targets, kinases and events of post-translational modifications. A Weighted gene co-expression network analysis (WGCNA) with all the 3020 N-responsive genes revealed 15 co-expression modules and their annotated biological roles. Protein-protein interaction network analysis of the main module revealed the hub genes and their functional annotation revealed their involvement in the ubiquitin process. Further, the occurrences of G-quadruplex sequences were examined, which are known to play important roles in epigenetic regulation but are hitherto unknown in N-response/NUE. Out of the 3020 N-responsive genes studied, 2298 contained G-quadruplex sequences. We compared these N-responsive genes containing G-quadruplex sequences with the 3601 genes we previously identified as NUE-related (for being both N-responsive and yield-associated). This analysis revealed 389 (17%) NUE-related genes containing G-quadruplex sequences. These genes may be involved in the epigenetic regulation of NUE, while the rest of the 83% (1811) genes may regulate NUE through genetic mechanisms and/or other epigenetic means besides G-quadruplexes. A few potentially important genes/processes identified as associated with NUE were experimentally validated in a pair of rice genotypes contrasting for NUE. The results from the WGCNA and G4 sequence analysis of N-responsive genes helped identify and shortlist six genes as candidates to improve NUE. Further, the hitherto unavailable segregation of genetic and epigenetic gene targets could aid in informed interventions through genetic and epigenetic means of crop improvement.

Overexpression of MYB-like transcription factor SiMYB30 from foxtail millet (Setaria italica L.) confers tolerance to low nitrogen stress in transgenic rice

Nitrogen fertilizers significantly increase crop yield; however, the negative impact of excessive nitrogen use on the environment and soil requires urgent attention. Improving crop nitrogen use efficiency (NUE) is crucial to increase yields and protect the environment. Foxtail millet (Setaria italica L.), a gramineous crop with significant tolerance to barren croplands, is an ideal model crop for studying abiotic stress resistance in gramineous crops. However, knowledge of the regulatory network for NUE in foxtail millet is fragmentary. Herein, we identified an R2R3-like MYB transcription factor in foxtail millet, SiMYB30, which belongs to MYB subfamily 17. The expression of SiMYB30 is responsive to low nitrogen (LN) concentration. Compared with wildtype Kitaake, seedlings of rice lines overexpressing SiMYB30 showed significantly increased shoot fresh and dry weights, plant height, and root area under LN treatment indoors. Consistently, overexpression of SiMYB30 in field experiments significantly increased grain and stem nitrogen contents, grain yield per plant, and stem weight in rice. Furthermore, qRT-PCR revealed that SiMYB30 effectively activated the expression of nitrogen uptake-related genes—OsNRT1, OsNRT1.1B, and OsNPF2.4—and nitrogen assimilation-related genes—OsGOGAT1, OsGOGAT2, and OsNIA2. Notably, SiMYB30 directly bound to the promoter of OsGOGAT2 and regulated its expression. These results highlight the novel and pivotal role of SiMYB30 in improving crop NUE.

Estimation of nitrogen nutrition index in chrysanthemum using chlorophyll meter readings

The nitrogen nutrition index (NNI) plays a critical role in improving crop nitrogen (N) diagnosis and predicting crop yield. Proximal sensing chlorophyll meters (CMs) have been widely used in precision agriculture, but few studies have focused on its utilization for estimating the NNI of chrysanthemum ( Dendranthema morifolium Ramat.). This study aimed to develop a model for NNI estimation in chrysanthemums using CM readings. Field experiments were conducted with five N fertilization treatments during two growing seasons (in 2019 and 2020). Chrysanthemum canopies were sampled across multiple days after planting (DAP) to determine plant N concentrations (PNC) and plant dry matter (PDM). CM measurements were recorded at defined DAP at different leaf layer positions (L1, L2, and L3 represent leaves that were 1/3, 1/2, and 2/3 apart from the top of the plant, respectively), and the normalized CM index (NCMI 1 , NCMI 2 , and NCMI 3 ) was calculated. All PNC and PDM data from the two seasons were then applied to fit the critical N (N c ) dilution curve using a Bayesian statistical model to estimate the NNI. Regression models were established to predict chrysanthemum NNI using CM readings and the NCMI as predictor variables. This study determined the N c of chrysanthemum to be N c = 2.318 ×PDM −0.204 . L1 was found to be the optimal leaf layer position for NNI estimation. Additionally, the NCMI-based prediction of NNI was found to be more reliable than that from the CM readings. NCMI 1 was the best predictor of chrysanthemum NNI across multiple DAP (NNI = 0.0741 ×e 2.6285NCMI1 , coefficient of determination = 0.59 *** , root mean square error = 0.110 NNI). The findings of this study can be applied to accurately predict chrysanthemum NNI from CM readings to provide technical support for N nutrition diagnosis in chrysanthemums. • This is the first study establishing the critical N dilution curve in chrysanthemum. • The upper leaf layer is optimal for chrysanthemum N nutrition index (NNI) estimations. • The normalized chlorophyll meter index showed to be the best predictor of chrysanthemum NNI .

Nitrogen Source Preference in Maize at Seedling Stage Is Mainly Dependent on Growth Medium pH

To improve crop nitrogen recovery efficiency (NRE), plants must be supplied with their preferred form of nitrogen (N). However, whether pH affects crop N-form preference remains unclear. Here, we aimed to explore how maize (Zea mays L.) preference for NH4+ and NO3− is affected by pH and to determine the critical pH controlling this preference. Maize plants were grown with NH4+ or NO3− in different soils (pH 4.32–8.14) and nutrient solutions (pH 4.00–8.00). After harvest, plant dry weights, N content, N uptake, NRE, soil pH, and exchangeable aluminum (Al) were measured. Compared with the effect of NO3−, NH4+ decreased maize dry weight, N uptake, and NRE by 28–94% at soil pHs of 4.32 and 4.36 and a solution pH of 4.00, whereas it increased these parameters by 10–88% at soil pHs of 6.52–8.02 and solution pHs of 7.00 and 8.00. NO3− increased soil pH and decreased soil exchangeable Al content at soil pHs of 4.32–6.68. Critical soil and solution pHs for changing plant growth and N uptake preference for NH4+ vs. NO3− ranged from 5.08 to 5.40 and from 5.50 to 6.59, respectively. In conclusion, the preference of maize seedling growth and N uptake for NH4+ vs. NO3− mainly depends on the pH of the growth medium, and maize seedlings generally prefer NO3− in strongly acid soils but NH4+ in neutral to alkaline soils.

A revised view on the evolution of glutamine synthetase isoenzymes in plants.

SUMMARYGlutamine synthetase (GS) is a key enzyme responsible for the incorporation of inorganic nitrogen in the form of ammonium into the amino acid glutamine. In plants, two groups of functional GS enzymes are found: eubacterial GSIIb (GLN2) and eukaryotic GSIIe (GLN1/GS). Only GLN1/GS genes are found in vascular plants, which suggests that they are involved in the final adaptation of plants to terrestrial life. The present phylogenetic study reclassifies the different GS genes of seed plants into three clusters: GS1a, GS1b and GS2. The presence of genes encoding GS2 has been expanded to Cycadopsida gymnosperms, which suggests the origin of this gene in a common ancestor of Cycadopsida, Ginkgoopsida and angiosperms. GS1a genes have been identified in all gymnosperms, basal angiosperms and some Magnoliidae species. Previous studies in conifers and the gene expression profiles obtained in ginkgo and magnolia in the present work could explain the absence of GS1a in more recent angiosperm species (e.g. monocots and eudicots) as a result of the redundant roles of GS1a and GS2 in photosynthetic cells. Altogether, the results provide a better understanding of the evolution of plant GS isoenzymes and their physiological roles, which is valuable for improving crop nitrogen use efficiency and productivity. This new view of GS evolution in plants, including a new cytosolic GS group (GS1a), has important functional implications in the context of plant metabolism adaptation to global changes.

Functional identification of bHLH transcription factor MdSAT1 in the ammonium response

Plants mainly uptake inorganic nitrogen from soil as ammonium and nitrate. Less energy is required to assimilate ammonium compared to nitrates, and plants prefer to take up ammonium when the external nitrogen concentration is low. Investigating the patterns and mechanisms of ammonium absorption can help improve crop nitrogen utilization. In this study, we isolated <italic>MdSAT1</italic>, a gene of apple encoding an ammonium-responsive bHLH transcription factor. MdSAT1 promoted the growth and development of lateral roots and root hairs. Overexpression of <italic>MdSAT1</italic> increased the transcript levels of genes related to ammonium uptake, indicating that MdSAT1 can regulate ammonium uptake and utilization at the transcriptional level. MdSAT1 also can modulate ROS accumulation to ultimately regulate plant growth. Taken together, these findings provide insight for us to further study the mechanisms by which <italic>MdSAT1</italic> controls ammonium utilization as well as plant growth and development.

Identification and characterization of apple MdNLP7 transcription factor in the nitrate response

Nitrogen is an essential nutrient for plant growth and development. Low utilization of nitrogen fertilizer during agricultural production causes a series of environmental problems, such as water eutrophication, soil acidity, and air pollution. Investigating the patterns and mechanisms of crop NO3− absorption and utilization therefore key to fully improving crop nitrogen utilization rates and promoting sustainable agricultural development. Apple is one of the most important horticultural crops in the world. Its nitrogen demand by apple during the growth period is very high, but few studies have been performed on apple genes, that regulate the NO3− response. Here, we found that the apple transcription factor MdNLP7 promoted nitrogen absorption and assimilation by activating the expression of MdNIA2 and MdNRT1.1. MdNLP7 also regulated H2O2 content by increasing catalase activity, which may also influence nitrate utilization. Our findings provide insight into the mechanisms by which MdNLP7 controls nitrate utilization in apple.

Contrasting effects of straw and straw-derived biochar applications on soil carbon accumulation and nitrogen use efficiency in double-rice cropping systems

Increasing cropland soil carbon (C) sequestration and improving crop nitrogen use efficiency (NUE) are vital for sustainable agriculture and environmental protection. The incorporation of straw and application of straw-derived biochar to croplands may help to achieve these goals; however, the long-term effects on soil C sequestration and NUE in double-rice cropping systems are poorly understood. Here, a 6-y field experiment was conducted in a double-rice cropping system to investigate the variations in soil C sequestration and NUE with straw and straw-derived biochar amendments. The treatments were as follows: control with zero nitrogen (N0); conventional chemical fertilizer application (NPK); NPK plus 3 t rice straw dry matter (DM) incorporated per ha−1 season−1 (NPK + LS); NPK plus 6 t rice straw DM incorporated per ha−1 season−1 (NPK + HS); NPK plus 24 t straw-derived biochar DM incorporated per ha−1 (NPK + LC) applied once; and NPK plus 48 t straw-derived biochar DM incorporated per ha−1 (NPK + HC) applied once. Both the straw and biochar additions increased the soil C content in the topsoil, and the NPK + LC treatment sequestered 2.6-fold more soil C than the NPK + HS treatment over the 6-y period, when the input amounts of straw as well as the straw derived C were similar for both treatments. Besides input C directly into the fields, biochar application also increased soil original organic C accumulation in the NPK + LC treatment. Compared with NPK, 50 % and 100 % straw incorporation to the field increased the mean NUE by 22.3 % and 39.8 %, respectively, in the late rice season of 4–6 y, mainly due to increasing soil organic C. Rice grain yields decreased in the early rice season for the first 3 y of the straw treatments but increased in the first season when the biochar was applied, when compared with NPK. However, in the second 3 y after straw application, the grain yield of NPK + HS was significantly higher than that of NPK in late rice season. This investigation has indicated that biochar application had a higher potential in soil carbon sequestration than straw incorporation, and long-term (> 3 y) straw incorporation favored for the enhancement of NUE in paddy fields.

Manipulating Amino Acid Metabolism to Improve Crop Nitrogen Use Efficiency for a Sustainable Agriculture.

In a context of a growing worldwide food demand coupled to the need to develop a sustainable agriculture, it is crucial to improve crop nitrogen use efficiency (NUE) while reducing field N inputs. Classical genetic approaches based on natural allelic variations existing within crops have led to the discovery of quantitative trait loci controlling NUE under low nitrogen conditions; however, the identification of candidate genes from mapping studies is still challenging. Amino acid metabolism is the cornerstone of plant N management, which involves N uptake, assimilation, and remobilization efficiencies, and it is finely regulated during acclimation to low N conditions and other abiotic stresses. Over the last two decades, biotechnological engineering of amino acid metabolism has led to promising results for the improvement of crop NUE, and more recently under low N conditions. This review summarizes current work carried out in crops and provides perspectives on the identification of new candidate genes and future strategies for crop improvement.

Genome-Wide Differential DNA Methylation and miRNA Expression Profiling Reveals Epigenetic Regulatory Mechanisms Underlying Nitrogen-Limitation-Triggered Adaptation and Use Efficiency Enhancement in Allotetraploid Rapeseed.

Improving crop nitrogen (N) limitation adaptation (NLA) is a core approach to enhance N use efficiency (NUE) and reduce N fertilizer application. Rapeseed has a high demand for N nutrients for optimal plant growth and seed production, but it exhibits low NUE. Epigenetic modification, such as DNA methylation and modification from small RNAs, is key to plant adaptive responses to various stresses. However, epigenetic regulatory mechanisms underlying NLA and NUE remain elusive in allotetraploid B. napus. In this study, we identified overaccumulated carbohydrate, and improved primary and lateral roots in rapeseed plants under N limitation, which resulted in decreased plant nitrate concentrations, enhanced root-to-shoot N translocation, and increased NUE. Transcriptomics and RT-qPCR assays revealed that N limitation induced the expression of NRT1.1, NRT1.5, NRT1.7, NRT2.1/NAR2.1, and Gln1;1, and repressed the transcriptional levels of CLCa, NRT1.8, and NIA1. High-resolution whole genome bisulfite sequencing characterized 5094 differentially methylated genes involving ubiquitin-mediated proteolysis, N recycling, and phytohormone metabolism under N limitation. Hypermethylation/hypomethylation in promoter regions or gene bodies of some key N-metabolism genes might be involved in their transcriptional regulation by N limitation. Genome-wide miRNA sequencing identified 224 N limitation-responsive differentially expressed miRNAs regulating leaf development, amino acid metabolism, and plant hormone signal transduction. Furthermore, degradome sequencing and RT-qPCR assays revealed the miR827-NLA pathway regulating limited N-induced leaf senescence as well as the miR171-SCL6 and miR160-ARF17 pathways regulating root growth under N deficiency. Our study provides a comprehensive insight into the epigenetic regulatory mechanisms underlying rapeseed NLA, and it will be helpful for genetic engineering of NUE in crop species through epigenetic modification of some N metabolism-associated genes.

Rice NIN-LIKE PROTEIN 1 rapidly responds to nitrogen deficiency and improves yield and nitrogen use efficiency.

Nitrogen (N) is indispensable for crop growth and yield, but excessive agricultural application of nitrogenous fertilizers has generated severe environmental problems. A desirable and economical solution to cope with these issues is to improve crop nitrogen use efficiency (NUE). Plant NUE has been a focal point of intensive research worldwide, yet much still has to be learned about its genetic determinants and regulation. Here, we show that rice (Oryza sativa L.) NIN-LIKE PROTEIN 1 (OsNLP1) plays a fundamental role in N utilization. OsNLP1 protein localizes in the nucleus and its transcript level is rapidly induced by N starvation. Overexpression of OsNLP1 improves plant growth, grain yield, and NUE under different N conditions, while knockout of OsNLP1 impairs grain yield and NUE under N-limiting conditions. OsNLP1 regulates nitrate and ammonium utilization by cooperatively orchestrating multiple N uptake and assimilation genes. Chromatin immunoprecipitation and yeast one-hybrid assays showed that OsNLP1 can directly bind to the promoter of these genes to activate their expression. Therefore, our results demonstrate that OsNLP1 is a key regulator of N utilization and represents a potential target for improving NUE and yield in rice.

Overexpression of OsMYB305 in Rice Enhances the Nitrogen Uptake Under Low-Nitrogen Condition.

Excessive nitrogen fertilizer application causes severe environmental degradation and drives up agricultural production costs. Thus, improving crop nitrogen use efficiency (NUE) is essential for the development of sustainable agriculture. Here, we characterized the roles of the MYB transcription factor OsMYB305 in nitrogen uptake and assimilation in rice. OsMYB305 encoded a transcriptional activator and its expression was induced by N deficiency in rice root. Under low-N condition, OsMYB305 overexpression significantly increased the tiller number, shoot dry weight and total N concentration. In the roots of OsMYB305-OE rice lines, the expression of OsNRT2.1, OsNRT2.2, OsNAR2.1, and OsNiR2 was up-regulated and 15NO3– influx was significantly increased. In contrast, the expression of lignocellulose biosynthesis-related genes was repressed so that cellulose content decreased, and soluble sugar concentration increased. Certain intermediates in the glycolytic pathway and the tricarboxylic acid cycle were significantly altered and NADH-GOGAT, Pyr-K, and G6PDH were markedly elevated in the roots of OsMYB305-OE rice lines grown under low-N condition. Our results revealed that OsMYB305 overexpression suppressed cellulose biosynthesis under low-nitrogen condition, thereby freeing up carbohydrate for nitrate uptake and assimilation and enhancing rice growth. OsMYB305 is a potential molecular target for increasing NUE in rice.

Exploring optimal nitrogen management practices within site-specific ecological and socioeconomic conditions

Abstract The “4R” fertilizer management principles of using the right rate, right source, right timing and right place is emergently required for enhancing crop production and improving crop Nitrogen Use Efficiency (NUE) in intensive small farming system. However, the methodology is still vague to design and implement technologies and management practices (TMPs) following the “4R” principles in these regions. This study designs various TMPs and evaluates their agronomic, environmental, and economic impacts in two typical intensive cereals cropping systems in China to explore how TMPs interact with biophysical conditions, and finally establish methodologies to recommend local optimal TMPs. Among 5 designed TMPs, the optimal TMPs for each site and cropping system were selected, which achieved the sustainable targets for productivity (80% of the achievable yield potential), NUE (0.60), and economic profitability. But several TMPs failed to satisfy the integrated targets, which implied the TMPs must be carefully designed to fit site-specific biophysical contexts. This work provided some basic guidelines for determining each “R”: The “Right rate” can be determined by balancing with crop aboveground N uptake where soil testing is not always available. The “Right timing” must consider the fertilizer products and local climatic features. Split application is not always better than one-time application, e.g., applying urea at 11th-leaf stage decreased spring maize yield by 9% at Lishu due to a 20-day sustained high temperature and drought condition. For the “Right source”, the adoption of enhanced efficiency fertilizers should take soil properties (especially soil pH) into consideration, e.g., urease inhibitors are effective in increasing NUE (by 44%) on alkaline soils, but the efficacy on acid soils is greatly reduced (by 19%). The “Right place” needs to be designed according to characteristics of crop root distribution and fertilizer sources, e.g., surface application of urease inhibitors in winter wheat gained greater NUE (0.62) and grain yield (8.3 Mg ha−1) than deep placement of urea and calcium ammonium nitrate. Considering the biophysical condition variations and its great influence on TMPs, a long-term trial research network to design, test and reshape the site-specific optimal TMPs following “4R” principles will be necessary.

The contribution of Stylosanthes guianensis to the nitrogen cycle in a low input legume-rice rotation under conservation agriculture

Background and aims Legumes integrated in crop rotations are intended to improve crop nitrogen (N) supply and yield. In conservation agriculture (CA) systems under low input conditions on highly weathered tropical soils, experimental evidence for these benefits is lacking. To understand the mechanisms and evaluate the impact of the legume N on the subsequent crop, an in-depth study on N dynamics in the soil-plant system was conducted.

Simple Assessment of Nitrogen Nutrition Index in Summer Maize by Using Chlorophyll Meter Readings.

Rapid and non-destructive diagnostic tools to accurately assess crop nitrogen nutrition index (NNI) are imperative for improving crop nitrogen (N) diagnosis and sustaining crop production. This study was aimed to develop the relationships among NNI, leaf N gradient, chlorophyll meter (CM) readings gradient, and positional differences chlorophyll meter index [PDCMI, the ratio of CM readings between different leaf layers (LLs) of crop canopy] and to validate the accuracy and stability of these relationships across the different LLs, years, sites, and cultivars. Six multi-N rates (0–320 kg ha−1) field experiments were conducted with four summer maize cultivars (Zhengdan958, Denghai605, Xundan20, and Denghai661) at two different sites located in China. Six summer maize plants per plot were harvested at each sampling stage to assess NNI, leaf N concentration and CM readings of different LLs during the vegetative growth period. The results showed that the leaf N gradient, CM readings gradient and PDCMI of different LLs decreased, while the NNI values increased with increasing N supply. The leaf N gradient and CM readings gradient increased gradually from top to bottom of the canopy and CM readings of the bottom LL were more sensitive to changes in plant N concentration. The significantly positive relationship between NNI and CM readings of different LLs (LL1 to LL3) was observed, yet these relationships varied across the years. In contrast, the relationships between NNI and PDCMI of different LLs (LL1 to LL3) were significantly negative. The strongest relationship between PDCMI and NNI which was stable across the cultivars and years was observed for PDCMI1−3 (NNI = −5.74 × PDCMI1−3+1.5, R2 = 0.76**). Additionally, the models developed in this study were validated with the data acquired from two independent experiments to assess their accuracy of prediction. The root mean square error value of 0.1 indicated that the most accurate and robust relationship was observed between PDCMI1–3 and NNI. The projected results would help to develop a simple, non-destructive and reliable approach to accurately assess the crop N status for precisely managing N application during the growth period of summer maize crop.