Rice Nitrogen Research Articles

Effect of Planting Time and Nitrogen Doses on Growth, Phenology and Yield of Basmati Rice (Oryza sativa L.) under Agro-Climatic Conditions of Haryana, India

A field experiment on rice was conducted at RRS, Kaul (Kaithal) of Chaudhary Charan Singh Haryana Agricultural University, Hisar during Kharif season of 2022 to find out optimum dose of nitrogen in rice under late planted condition for getting higher yield. The transplantation get delayed because of shortage of labour and water during the brief transplanting period, which may affect the crop yield adversely under late planting. Soil of experimental field was sandy clay loam texture, alkaline in reaction (7.81), low in organic carbon (0.39%), available nitrogen (130 kg ha-1) and medium in available phosphorous (24 kg ha-1) and high in available potash (480 kg ha-1). The experiment included two transplanting dates (P1: First week of July and P2: Fourth week of July), five levels of N application (N1:0, N2:30, N3:60, N4:90, N5:120 kg N ha-1) laid out in factorial randomised block design. The growth parameters viz. plant height (cm), number of tillers m-2 and dry matter accumulation (g) were reduced significantly under late planting (P2). The yield (grain and straw) of the rice crop increased with each successive increase in N level, although the response was only significant up to 90 kg ha-1. The interaction between planting time and N levels was found to be significant in terms of grain yield, revealing that dose of 90 kg ha-1 was sufficient in timely transplanted rice crops (1st week of July), whereas late transplanted crops (4th week of July) may require a higher dose of N (120 kg ha-1) to get higher yield. However, the highest yield was obtained when the crop was timely transplanted (1st week of July) and supplied 90 kg of N ha-1.

Low phosphorus promotes NSP1–NSP2 heterodimerization to enhance strigolactone biosynthesis and regulate shoot and root architecture in rice

Phosphorus is an essential macronutrient for plant development and metabolism, and plants have evolved ingenious mechanisms to overcome phosphate (Pi) starvation. However, the molecular mechanisms underlying the regulation of shoot and root architecture by low phosphorus conditions and the coordinated utilization of Pi and nitrogen remain largely unclear. Here, we show that Nodulation Signaling Pathway 1 (NSP1) and NSP2 regulate rice tiller number by promoting the biosynthesis of strigolactones (SLs), a class of phytohormones with fundamental effects on plant architecture and environmental responses. We found that NSP1 and NSP2 are induced by Oryza sativa PHOSPHATE STARVATION RESPONSE2 (OsPHR2) in response to low-Pi stress and form a complex to directly bind the promoters of SL biosynthesis genes, thus markedly increasing SL biosynthesis in rice. Interestingly, the NSP1/2–SL signaling module represses the expression of CROWN ROOTLESS 1 (CRL1), a newly identified early SL-responsive gene in roots, to restrain lateral root density under Pi deficiency. We also demonstrated that GR244DO treatment under normal conditions inhibits the expression of OsNRTs and OsAMTs to suppress nitrogen absorption but enhances the expression of OsPTs to promote Pi absorption, thus facilitating the balance between nitrogen and phosphorus uptake in rice. Importantly, we found that NSP1p:NSP1 and NSP2p:NSP2 transgenic plants show improved agronomic traits and grain yield under low- and medium-phosphorus conditions. Taken together, these results revealed a novel regulatory mechanism of SL biosynthesis and signaling in response to Pi starvation, providing genetic resources for improving plant architecture and nutrient-use efficiency in low-Pi environments.

Variation Characteristics and Expression State of Nitrogen and Phosphorus Metering Ratio of Rice in Black Soil under Film Mulching and Irrigation Methods

In order to investigate the effects of film mulching and water-saving methods on soil inorganic nitrogen, nitrogen content of rice organs, nitrogen-phosphorus metering ratio, and nutrient limitation during rice yield formation, two water-saving irrigation methods and black biodegradable film mulching were adopted. The effects of water-saving film mulching on NH4+-N and NO3−-N in 0 to 60 cm soil, nitrogen accumulation and ratio, and nitrogen-phosphorus metering ratio in rice organs were analyzed. The nitrogen-phosphorus-limiting state of rice growth under water-saving film mulching was determined. The results showed that water-saving and film mulching methods could weaken the leaching of NH4+-N and NO3−-N and enhance the nitrogen uptake of rice. The water-saving method of mulching could reduce the metering ratio of nitrogen and phosphorus in rice organs. The panicle maturity process had been in a state of nitrogen limitation, and the effect was gradually enhanced. The nitrogen and phosphorus metering ratio of panicles was positively correlated with NH4+-N accumulation in the 0 to 60 cm soil layer and nitrogen accumulation of rice organs, and negatively correlated with soil NO3−-N accumulation under film mulching and water-saving methods. The correlation between stems and leaves’ nitrogen and phosphorus metering ratios and influencing factors was basically opposite to that of panicles’ nitrogen and phosphorus metering ratio. This study can provide a reference for the formulation of a fertilization system under film mulching in the black soil region of northeast China.

Integrated nutrient management module to improve productivity and economics of short grain aromatic rice (Oryza sativa)- greengram (Vigna radiata) sequence

The present field study was carried out during 2017–18 and 2018–19 rainy (kharif) and winter (rabi) seasons in order to examine the impact caused by integrated nutrient management (INM) on the yield and quality of the short grain aromatic rice (Oryza sativa L.)-greengram (Vigna radiata L.) combination. Two years experimental data concluded that integration of 50% recommended dose (RD) as fertilizer + 50% RD of nitrogen via farm yield manure (FYM) resulted in considerably higher economic yield (3837.1 and 3917.7 kg/ha) of short grain aromatic rice cv. Nua Acharamati which were at par with 75% RD as fertilizer + green manuring of dhaincha (3438.5 and 3539.1 kg/ha). Pooled data revealed that, residual effect of 50% RD as fertilizer + 50% RD of nitrogen (FYM) and 75% RD as fertilizer + Rhizobium + PSB in greengram recorded the highest number of pods/plant (18.2), seeds/pod (11.3), pod length (9.3 cm), test weight (32.7 g), seed yield (925.7 kg/ha) and stover yield (2240.7 kg/ha) in greengram cv. IPM-02-03. Application of 50% RD as fertilizer + 50% RD of nitrogen (FYM) to aromatic rice recorded the highest hulling recovery (75.8 and 75.5%), milling recovery (68.0 and 68.3%), head rice recovery (60.0, 59.7%) and crude protein content (8.75 and 9.11%) during both of the years experiment being at par with application of 75% RD as fertilizer + green manuring. Economics of the system revealed the highest gross return, net return and B:C ratio by application of 50% RD as chemical fertilizer + 50% RD of nitrogen (FYM) in rice followed by 75% RD as chemical fertilizer + Rhizobium + PSB in greengram.

Mitigating the adverse effect of warming on rice canopy and rhizosphere microbial community by nitrogen application: An approach to counteract future climate change for rice

The adverse impact of climate change on crop production continues to increase, necessitating the development of suitable strategies to mitigate these effects and improve food security. Several studies have revealed how global warming negatively impacts the grain-filling stage of rice and that this effect could be mitigated by nitrogen; however, the impact of nitrogen application on rice canopy and rhizosphere microbial communities remains unclear. We conducted a study using an open-field warming system. Results showed that warming influenced rice canopy by decreasing aboveground biomass and harvest index, whereas nitrogen application had positive effect on rice production under warming conditions by increasing the plant nitrogen content, biomass, harvest index and soil fertilities. Moreover, soil ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3−-N) contents were significantly decreased under warming, which were higher after nitrogen application. Notably, warming and nitrogen fertilizer caused 19 % (P < 0.01) and 7 % (P < 0.05) variations, respectively, in the β diversity of the microbial community, respectively. The impact of warming was significant on NH4+-N-related microorganisms; however, this impact was weakened by nitrogen application for microbes in the rhizosphere. This study demonstrated that enhanced nitrogen fertilizer can alleviate the adverse impact of warming by weakening its effects on rhizosphere microbes, improving soil fertility, promoting rice nitrogen uptake, and increasing the aboveground biomass and harvest index. These findings provide an important theoretical basis for developing practical, responsive cultivation strategies.

Development and Test of Rice Nitrogen Nutrition Index Estimation Model Based on Airborne Multi-Spectrum

Both excessive and deficient nitrogen (N) concentration in the growing media can affect the growth, development, yield, and quality of rice. Traditional methods of N determination of plant require destructive and rigorous sampling, which is also time-consuming and laborious. However, rapid and non-destructive nitrogen diagnosis has become an important area of research in precision agriculture. Heilongjiang Province, China is a cold climate rice growing area, where the growth and fertilization of rice follows a definite pattern. In the present study, two varieties of rice (Wuyoudao4 and Songjing9) and as location Heilongjiang Province were selected. Nitrogen diagnosis of rice was carried out based on airborne multi-spectrum methodology. Canopy spectral data of rice at key growth periods were obtained by using a UAV equipped with a multi-spectral camera, and agronomic parameters such as leaf N content and dry matter weight were obtained synchronically. An airborne multispectral canopy normalized vegetation index (NDVI) model for N diagnosis based on its critical concentration curve was established as a nondestructive N diagnosis of rice for cold region. Results showed that canopy NDVI can estimate rice nitrogen nutrition index (NNI) properly over the growth period. The coefficient of determination R2, root mean square error (RMSE) and standard root mean square error (nRMSE) were compared to determine the best effect of the index model. The interphase nitrogen diagnosis model of WYD-4 based on NDVI for cold region was as follows: NNI=0.3916e1.0809*NDVI (RMSE=0.12, nRMSE=12.43%), SJ-9: NNI=0.3325e1.2705*NDVI (RMSE=0.10, nRMSE =10.36%), indicating that the established model can better estimate the nitrogen status of rice. Bangladesh J. Bot. 52(2): 529-538, 2023 (June) Special

Effects of local nitrogen supply and nitrogen fertilizer variety coupling on rice nitrogen transport and soil nitrogen balance in paddy fields

IntroductionThis study aimed to provide the theoretical basis for formulating scientific and reasonable on-farm nitrogen (N) management measures and efficient strategic fertilization to understand the effects of localized N supply (LNS) and N fertilizer variety coupling on N transport and soil N balance in rice fields.MethodsA 2-year field experiment (2020 and 2021) was conducted in Jingzhou, Hubei Province, which included the following six treatments: no N application (CK), farmers' fertilizer practice (FFP), and four LNS treatments, including two N application methods including mechanical side-deep fertilization (M) and root-zone fertilization (R), two N fertilizer types with urea (U), and controlled-release urea (CRU).ResultsCompared with FFP, LNS increased the N apparent translocation level from stems, sheathes, and leaves (TNT) and N uptake by 10.70–50.59% and 11.28–29.71%, respectively. In LNS, the levels of nitrite reductase (NR), glutamine synthetase (GS), and glutamate synthase (GOGAT) under R increased by 13.81, 9.56, and 15.59%, respectively, compared with those under M, resulting in a significant increase in TNT by 8.58% and N uptake by 1.87%. Regarding the N fertilizer type, CRU significantly increased chlorophyll content by 7.27%, superoxide dismutase (SOD) and catalase (CAT) by 14.78 and 29.95% (p &amp;lt; 0.05), and NR, GS, and GOGAT by 44.41, 16.12, and 28.41% (p &amp;lt; 0.05), respectively, compared with that in U, which contributed to N absorption and transport. Moreover, CRUR significantly decreased N apparent loss by 50.04% compared with CRUM (p &amp;lt; 0.05).DiscussionConsidering the risk of soil N leaching and environmental protection, R should be selected as the recommended fertilization method. The combination of CRU and R is the most effective fertilization approach.

Nitrogen and phosphorus fertilization in upland rice in the municipality of Humaitá at Amazonas State

Nitrogen and phosphorus fertilization in upland rice in the municipality of Humaitá at Amazonas State

Large-scale exploration of nitrogen utilization efficiency in Asia region for rice crop: Variation patterns and determinants.

Improving rice nitrogen utilization efficiency (NUtE) is imperative to maximizing future food productivity while minimizing environmental threats, yet knowledge of its variation and the underlying regulatory factors is still lacking. Here, we integrated a dataset with 21,571 data compiled by available data from peer-reviewed literature and a large-scale field survey to address this knowledge gap. The overall results revealed great variations in rice NUtE, which were mainly associated with human activities, climate conditions, and rice variety. Specifically, N supply rate, temperature, and precipitation were the foremost determinants of rice NUtE, and NUtE responses to climatic change differed among rice varieties. Further prediction highlighted the improved rice NUtE with the increasing latitude or longitude. The indica and hybrid rice exhibited higher NUtE in low latitude regions compared to japonica and inbred rice, respectively. Collectively, our results evaluated the primary drivers of rice NUtE variations and predicted the geographic responses of NUtE in different varieties. Linking the global variations in rice NUtE with environmental factors and geographic adaptability provides valuable agronomic and ecological insights into the regulation of rice NUtE.

Performance of Promising Rice Genotypes as Affected by Different Nitrogen Levels in Central Terai of Nepal

Application of appropriate level of nitrogen (N) for rice is a key to increase nitrogen use efficiency thereby yields. Six rice genotypes under six N levels were evaluated in a split plot design with three replications under irrigated conditions in National Rice Research Program, Dhanusha during 2020 with the objective of determining the high yielding variety and the best dose of N for obtaining higher yield. The six rice genotypes were NR 2168, NR 2158, NR 2157-122, NR 2175, NR 2182 and PR 126 while various N levels were 0. 75, 100, 125, 150 and 175 kg N ha-1. The results indicated that NR 2182 recorded the highest grain yield of 5.28 t ha-1 while PR 126 recorded the lowest grain yield 3.98 t ha-1. A linear increase in grain yield was observed with a continuous increase in N level from 0 to 150 kg ha-1 while it decreased thereafter. The grain yield was significantly higher with the application of 150 kg N ha-1 as compared to control. Agronomic N use efficiency for studied rice genotypes varied significantly and ranged from negative to 12.63 kg grain yield per kg of N applied. NR 2182 recorded the highest value of agronomic nitrogen use efficiency for the N level of 150 kg ha-1. It can be concluded that increasing nitrogen levels resulted in significant variations in the response of different varieties, with all varieties consistently recording lower yields at highest N levels. Thus, opting for an intermediate N level appears both economically prudent and environmentally sustainable.

Increasing Nitrogen Fertilizer Application Is a Feasible Strategy to Mitigate Rice Yield Reduction in Wet Year

Rice production is intimately related to water and nitrogen management, whereas rice yield inevitably decreases with extreme rainfall. Optimization of water and nitrogen management may mitigate the degree of rice yield reduction. Hence, we conducted a field experiment in a normal and wet year to investigate suitable water and nitrogen management that could reduce the risk of rice yield reduction. The field experiment comprised six water and nitrogen management methods, which included two irrigation methods (CF: continuous flooding; AWD: alternating wet and dry) and three nitrogen fertilizer levels (N0, N90, and N180: 0, 90, and 180 kg N ha−1, respectively). The results showed an average yield reduction of 23.5% in the wet year compared to normal year. The nitrogen rate of N0, N90, and N180 resulted in a 36.9%, 24.8%, and 11.0% of yield reduction in the wet year, which presented a decrease in yield reduction with the increase in nitrogen rate. Panicle contributed over almost 60% and 75% on average to biomass and total nitrogen uptake, but both the total amount and proportion of nitrogen uptake in panicle showed a decrease in the wet year. In addition, the rice yield showed a significant positive correlation with nitrogen uptake both in the normal and wet year. Therefore, in the wet year, the decrease in nitrogen uptake in panicle results in a yield reduction. With the increase in nitrogen rate, the nitrogen internal use efficiency (IEN) was significantly decreased in the normal year, while it increased in the wet year, and the nitrogen recovery use efficiency (REN) and nitrogen harvest index (HIN) were not affected by nitrogen rate. Therefore, these results suggested that increased nitrogen rate in a wet year could improve rice nitrogen uptake to reduce the risk of yield reduction and maintain the nitrogen use efficiency (NUE).

Integrated transcriptomic analysis identifies coordinated responses to nitrogen and phosphate deficiency in rice.

Nitrogen (N) and phosphorus (P) are two primary components of fertilizers for crop production. Coordinated acquisition and utilization of N and P are crucial for plants to achieve nutrient balance and optimal growth in a changing rhizospheric nutrient environment. However, little is known about how N and P signaling pathways are integrated. We performed transcriptomic analyses and physiological experiments to explore gene expression profiles and physiological homeostasis in the response of rice (Oryza sativa) to N and P deficiency. We revealed that N and P shortage inhibit rice growth and uptake of other nutrients. Gene Ontology (GO) analysis of differentially expressed genes (DEGs) suggested that N and Pi deficiency stimulate specific different physiological reactions and also some same physiological processes in rice. We established the transcriptional regulatory network between N and P signaling pathways based on all DEGs. We determined that the transcript levels of 763 core genes changed under both N or P starvation conditions. Among these core genes, we focused on the transcription factor gene NITRATE-INDUCIBLE, GARP-TYPE TRANSCRIPTIONAL REPRESSOR 1 (NIGT1) and show that its encoded protein is a positive regulator of P homeostasis and a negative regulator of N acquisition in rice. NIGT1 promoted Pi uptake but inhibited N absorption, induced the expression of Pi responsive genes PT2 and SPX1 and repressed the N responsive genes NLP1 and NRT2.1. These results provide new clues about the mechanisms underlying the interaction between plant N and P starvation responses.

Estimating the rice nitrogen nutrition index based on hyperspectral transform technology.

The rapid diagnosis of rice nitrogen nutrition is of great significance to rice field management and precision fertilization. The nitrogen nutrition index (NNI) based on the standard nitrogen concentration curve is a common parameter for the quantitative diagnosis of rice nitrogen nutrition. However, the current NNI estimation methods based on hyperspectral techniques mainly focus on finding a better estimation model while ignoring the relationship between the critical nitrogen concentration curve and rice hyperspectral reflectance. This study obtained canopy spectral data using unmanned aerial vehicle (UAV) hyperspectral remote sensing and determined the rice critical nitrogen concentration curve and NNI. Taking the spectrum at critical nitrogen concentration as the standard spectrum, the original spectral reflectance and logarithmic spectral reflectance data were transformed by the difference method, and the features of the spectral data were extracted by a Autoencoder. Finally, the NNI inversion models of rice based on Extreme Learning Machine (ELM) and Bald Eagle Search-Extreme Learning Machine (BES-ELM) were constructed by taking the feature bands of four spectral extractions as input variables. 1) from the feature extraction results of the self-encoder, simple logarithmic or difference transformation had little effect on NNI estimation, and logarithmic difference transformation effectively improved the NNI estimation results; 2) the estimation model based on the logarithmic difference spectrum and BES-ELM had the highest estimation accuracy, and the coefficient of determination (R2) values of the training set and verification set were 0.839 and 0.837, and the root mean square error (RMSE) values were 0.075 and 0.073, respectively; 3) according to the NNI, the samples were divided into a nitrogen-rich group (NNI ≥ 1) and nitrogen-deficient group (NNI < 1). The logarithmic difference transformation of the spectrum can effectively improve the estimation accuracy of the NNI estimation model, providing a new approach for improving NNI estimation methods based on hyperspectral technology.

CRISPR/Cas9 and Agrobacterium tumefaciens virulence proteins synergistically increase efficiency of precise genome editing via homology directed repair in plants.

CRISPR/Cas9 genome editing and Agrobacterium tumefaciens-mediated genetic transformation are widely-used plant biotechnology tools derived from bacterial immunity-related systems, each involving DNA modification. The Cas9 endonuclease introduces DNA double-strand breaks (DSBs), and the A. tumefaciens T-DNA is released by the VirD2 endonuclease assisted by VirDl and attached by VirE2, transferred to the plant nucleus and integrated into the genome. Here, we explored the potential for synergy between the two systems and found that Cas9 and three virulence (Vir) proteins achieve precise genome editing via the homology directed repair (HDR) pathway in tobacco and rice plants. Compared with Cas9T (Cas9, VirD1, VirE2) and CvD (Cas9-VirD2) systems, the HDR frequencies of a foreign GFPm gene in the CvDT system (Cas9-VirD2, VirD1, VirE2) increased 52-fold and 22-fold, respectively. Further optimization of the CvDT process with a donor linker (CvDTL) achieved a remarkable increase in the efficiency of HDR-mediated genome editing. Additionally, the HDR efficiency of the three rice endogenous genes ACETOLACTATE SYNTHASE (ALS), PHYTOENE DESATURASE (PDS), and NITROGEN TRANSPORTER 1.1 B (NRT1.1B) increased 24-, 32- and 16-fold, respectively, in the CvDTL system, compared with corresponding Cas9TL (Cas9T process with a donor linker). Our results suggest that collaboration between CRISPR/Cas9 and Agrobacterium-mediated genetic transformation can make great progress towards highly efficient and precise genome editing via the HDR pathway.

Influence of nitrogen and weed-management practices on crop-growth indices and productivity of dry direct-seeded rice (Oryza sativa)

A field study was carried out during the rainy (kharif) season of 2019–20 at ICAR-Indian Agricultural Research Institute, New Delhi, to study the effect of nitrogen and weed management practices in dry direct-seeded rice (Oryza sativa L.) for obtaining higher productivity and crop growth. The experiment was laid out in a split-plot design, taking 3 nitrogen treatments, i.e. No N (P and K only), recommended dose of fertilizer (RDF–N : P : K = 80 : 17 : 33 kg/ha) (3 splits of nitrogen application–50% basal + 25% at tillering + 25% at panicle-initiation stage), 50% N from FYM + 50% N as real-time nitrogen management (top-dressing) as per leaf colour chart (LCC) up to panicle-initiation stage in main plots. Four weed-management treatments, viz. unweeded control, weed-free control, Pendimethalin @ 1.5 kg a.i./ha as pre-emergence followed by (fb) brown manuring with Sesbania bispinosa (Jacq.) W. Wight; Syn. S. aculeata [(Willd.) Pers.] (knocking down Sesbania by Bispyribac- Na 25 g a.i./ha at 25 days after sowing (DAS), Pendimethalin @ 1.5 kg a.i./ha as pre-emergence fb Bispyribac -Na @ 25 g a.i./ha at 25 DAS in subplots with 3 replications. Result revealed that, Pendimethalin @ 1.5 kg a.i./ha as pre-emergence fb brown manuring with Sesbania bispinosa significantly increased grain yield (2.78 t/ha) as well as growth indices like leaf-area index (1.8 and 4.4 at 40 DAS and 70 DAS, respectively), crop-growth rate (1.9 g/m2 /day, 8.8 g/m2 /day at 40 DAS and 70 DAS, respectively), relative growth rate (145.3 mg/g/day and 54.5 mg/g/day 40 DAS and 70 DAS, respectively), net assimilation rate (0.40 g/m2 /day 3.49 g/m2/day at 40 DAS and 70 DAS, respectively) and dry-matter accumulation (185.6 g/m2 , 591.6 g/m2 and 1,144 g/m2 at 40 DAS, 70 DAS and harvesting, respectively) to the other treatments. In case of N-management practices, combined use of FYM and LCC-based N management gave the highest grain yield (3.25 t/ha), growth indices like leaf-area index (1.69 and 4.0 at 40 DAS and 70 DAS respectively) crop-growth rate (1.8 g/m2/day, 8.2 g/m2/day at 40 DAS and 70 DAS, respectively), relative growth rate (145.1 mg/g/day and 55.1 mg/g/day at 40 DAS and 70 DAS, respectively) and dry-matter accumulation (168.5 g/m2 , 523.2 g/m2 and 958 g/m2 at 40 DAS, 70 DAS and harvesting, respectively) comparable with RDF application and significantly higher than the plot without N.

OsNAR2.1 induced endogenous nitrogen concentration variation affects transcriptional expression of miRNAs in rice.

The studies of rice nitrogen concentration on the expression of miRNA so far are mostly limited to the exogenous nitrogen, leaving the effect of endogenous nitrogen largely unexplored. OsNAR2.1 is a high-affinity nitrate transporter partner protein which plays a central role in nitrate absorption and translocation in rice. The expression of OsNAR2.1 could influence the concentration of the endogenous nitrogen in rice. We showed that the expression and production of miRNA in rice can be influenced by manipulating the endogenous nitrogen concentration via OsNAR2.1 transgenic lines. The small RNA content, particularly 24 nucleotides small RNA, expressed differently in two transgenic rice lines (nitrogen efficient line with overexpression of OsNAR2.1 (Ov199), nitrogen-inefficient line with knockdown OsNAR2.1 by RNAi (RNAi)) compared to the wild-type (NP). Comparative hierarchical clustering expression pattern analysis revealed that the expression profiles of mature miRNA in both transgenic lines were different from NP. Several previously unidentified miRNAs were identified to be differentially expressed under different nitrogen concentrations, namely miR1874, miR5150, chr3-36147, chr4-27017 and chr5-21745. In conclusion, our findings suggest that the level of endogenous nitrogen concentration variation by overexpression or knockdown OsNAR2.1 could mediate the expression pattern and intensity of miRNA in rice, which is of high potential to be used in molecular breeding to improve the rice responses towards nitrogen utilization.

Application of milk vetch (Astragalus sinicus L.) with reduced chemical fertilizer improves rice yield and nitrogen, phosphorus, and potassium use efficiency in southern China

Milk vetch (Astragalus sinicus L.; MV) is the most common winter green manure used in rice cropping systems in southern China. The utilization of MV can achieve the dual goals of soil fertilization and increased rice yield. Two long-term field experiments were conducted in Yujiang and Gaoan in Jiangxi Province, a typical double-rice cropping area, to explore the effects of 80 % conventional fertilizer for early rice supplemented with 15.0 (G1F80), 22.5 (G2F80), 30.0 (G3F80), and 37.5 (G4F80) t ha−1 MV on rice yield, soil fertility, nutrient uptake, and nutrient use efficiency. The results showed that, the yield data obtained from the 5-year (Gaoan) and 12-year (Yujiang) long-term experiments demonstrated that compared with conventional fertilization (F100), treatments with MV markedly increased the yield of early and late rice by 2.5–8.8 % and 5.6–10.9 %, respectively, and high rates of MV (G3F80 and G4F80) performed better in grain yields. The nitrogen (N) and potassium (K) uptake of early rice in Gaoan increased by 38.1 and 34.8 kg ha−1, respectively, and the N uptake of late rice in Gaoan and Yujiang increased by 11.7 and 62.6 kg ha−1 in G2F80, respectively, compared to that in F100. Compared with F100, treatments with MV significantly increased phosphorus (P) fertilizer recovery efficiency by 23.1–36.4 %, and the agronomic efficiency of N, P, and K fertilizers increased by 16.1–21.1 %, 13.9–19.6 %, and 15.7–21.4 %, respectively. Partial least squares path model analysis indicated that soil available P was the most important factor affecting the nutrient uptake of rice, and available K was the most important factor affecting fertilizer use efficiency. Our results suggested that 22.5 t ha−1 MV supplemented with 80 % chemical fertilizer is recommended for double-rice cropping sites to improve rice yield and crop uptake and the use efficiency of N, P, and K fertilizers.

The Yield-Forming Role of Nitrogen in Rice in the Growing Seasons with Variable Thermal Conditions

A reduced basal and increased topdressing fertilizer rate (RBIT) can usually increase rice yield, but whether this practice alleviates the impact of poor weather on rice production is unknown. Thus, the effect of three integrated RBIT treatments (RBITs, including RBIT alone, RBIT in combination with straw incorporation (RBITS) or a reduced fertilizer rate (RBITR)) on rice growth and nutritional status under different weathers was investigated in a 9-year experiment. Conventional fertilization (CF) was the control. We found that daytime temperature and light (DTL) after heading were the main meteorological factors limiting rice yield increases. RBITs did not affect rice yield under High-DTL, compared with CF, but RBITS significantly increased rice yield under Low-DTL. Compared with High-DTL, the positive effect of RBIT and RBITR on the N concentration and proportion in vegetative organs under Low-DTL was higher than the K concentration in vegetative organs, but RBITS showed the opposite trend. Regression analysis indicated that the harvest index had stronger correlations with the N concentration (negative), K concentration (positive), and N/K (negative) in vegetative organs under Low-DTL than under High-DTL. Our findings suggested that RBITS could improve rice adaptability to daytime temperature and light changes after heading by balancing crop nutritional status (N/K).

Effect of Leaf Surface Regulation of Zinc Fertilizer on Absorption of Cadmium, Plumbum and Zinc in Rice (Oryza sativa L.)

The accumulation of heavy metals in rice is bound to affect human health and safety. In order to ensure food security, this study explores the effect of leaf surface regulation of zinc (Zn) fertilizer on the safety of rice in cadmium (Cd)-plumbum (Pb) polluted farmland. Through field experiments, the leaf surface control treatment of zinc fertilizer was set up, and the effects of leaf surface control of zinc fertilizer on rice yield, Cd and Pb concentration in different parts and zinc, nitrogen, phosphorus and potassium concentration in brown rice were studied in the growing period of rice. The results showed as follows: (1) Spraying twice or more in the growth stage of rice could increase the yield by 6.77–7.29% compared with the blank, which was significantly higher than that of single spraying in a certain growth stage. (2) After spraying zinc fertilizer on the leaf surface, Cd and Pb concentration in brown rice decreased by 29.52–56.01% and 11.10–28.34%, respectively, compared with CK. Two or more times of spraying can make Cd concentration in brown rice meet the Chinese standard GB 2762-2022, and one time of spraying can make Pb concentration in brown rice meet the standard. (3) Leaf surface control of zinc fertilizer could reduce the Cd enrichment ability of rice plant parts, and the Cd enrichment coefficient of brown rice was significantly reduced by 28.18–55.02%. Leaf surface control of zinc fertilizer can reduce Cd and Pb concentration in brown rice by reducing the transport ability of heavy metal Cd and Pb in rice roots to straw and then to brown rice. (4) The zinc concentration in brown rice was 18.16–20.68 mg·kg−1, which was 18.21–34.64% higher than that in CK, and the zinc enrichment effect was the most significant after spraying three times. Meanwhile, the nitrogen, phosphorus and potassium concentration in brown rice also increased with the increase of spraying times. By comprehensive analysis, the leaf surface control of zinc fertilizer can reduce the Cd and Pb concentration in rice, and the Cd and Pb concentration in brown rice can meet the Chinese standard GB 2762-2022 by spraying twice. At the same time, it can improve the concentration of zinc, nitrogen, phosphorus and potassium in brown rice, is feasible and has high economic benefits.

Effect of nutrient management practices on nitrogen, phosphorus and yield of lowland rice in Eastern Himalayan region

Effect of nutrient management practices on nitrogen, phosphorus and yield of lowland rice in Eastern Himalayan region