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[Objective] To clarify the effects of nitrogen fertilization operation on maize yield and nitrogen utilization efficiency under drip irrigation in Tumochuan plain of Inner Mongolia, and explore the feasibility of using the nitrogen nutrient index as monitoring index to diagnose the nitrogen nutrient status of maize under drip irrigation with water and fertilization integration in Tumochuan plain. [Methods] The nitrogen nutrient content of mazie under 3 nitrogen fertilization rates (0,270,360 kg/hm²) and 3 and 5 nitrogen fertilization rates during the whole growth period were tested in Tumed Right Banner of Baotou City and Tumed Left Banner of Hohhot City in Inner Mongolia from 2022 to 2023. The yield and nitrogen utilization efficiency of maize were studied by using variance analysis and statistical modeling. The changes of canopy nitrogen concentration and aboveground biomass were analyzed and construct a critical nitrogen concentration dilution curve model. [Results] Increasing the rate and times of nitrogen application could significantly increase ear number, grain number per ear and 1 000-grain weight of maize, thus increasing yield. In addition, increasing nitrogen application times could significantly improve nitrogen utilization efficiency of maize (P<0.05). Nitrogen application rate increased from 270 kg/hm² to 360 kg/hm², and the average annual yield increased by 5.79%. Nitrogen application times increased from 3 times to 5 times, and the average annual yield and nitrogen utilization efficiency increased by 3.15% and 22.25%, respectively. The critical nitrogen concentration dilution curve of maize for drip irrigation in Tumochuan plain is N=3.36W-2, R²=0.94,P<0.05, and the validation accuracy RMSE, NRMSE and MAE were 0.40%, 11.50% and 0.20%, respectively. The stability of the model was good. According to the model calculation, when the nitrogen application rate was 270 kg/hm² the corresponding suitable nitrogen application times were 5 times, and the ratio of 15:25:35:15:10 was applied at 4 leaf extension stage, 8 leaf extension stage, 12 leaf extension stage, silking stage and milking stage, respectively, the mazie yield was the best, was 14.09 t/hm². In this area, the nitrogen fertilization requirements at jointing stage, 9 leaf extension stage, 12 leaf extension stage, silking stage and milking stage were -3.42 to 15.29,-16.80 to 22.90,-26.86 to 62.32 and -54.65 to 85.14 and -48.18 to 111.80 kg/hm². [Conclusion] Appropriate increase of nitrogen application rate and nitrogen application times can significantly improve maize yield and nitrogen utilization efficiency in Tumochuan plain of Inner Mongolia. The critical nitrogen concentration dilution curve model of maize under drip irrigation in Tumochuan plain of Inner Mongolia can effectively identify the nitrogen nutrient status of maize plants from the jointing stage to the milking stage and calculate and recommend the appropriate fertilization application rate, so as to realize the on-demand operation of maize growth. [ABSTRACT FROM AUTHOR]

The nitrogen nutrition index (NNI) as an effective indicator for monitoring crop nitrogen (N) status has multiple applications in agriculture, such as estimating in-season crop N requirement (NR), predicting crop biomass/yield, and improving N use efficiency. The present study was aimed to develop basil (Ocimum basilicum L.) NR and relative biomass (RB) prediction models based on the concept of critical N concentration. Two experiments were carried out with different N application rates in the research greenhouse of University of Tehran, Iran. Basil NNI values were calculated using the previously developed critical N dilution curve. Subsequently, the in-season basil NR estimation model was developed as a function of NNI, N recovery efficiency (NRE) and plant age. Additionally, basil RB was simulated as a function of the averaged and integrated NNI based on a linear-plateau model. Moreover, a theoretical relationship between N utilization efficiency (NUtE) and the NNI was established. The validation results of the developed NR-NNI model demonstrated a good performance with a root mean square error (RMSE) and a normalized root mean square error (NRMSE) less than 5.28 kg ha−1 and 4.72%, respectively. The results showed that crop biomass and NNI were the most significant explanatory factors for the variations in basil NUtE. Therefore, the crop NNI can serve as a practical in-season diagnostic tool for basil NR and RB prediction, while also contributing to the design of decision support systems and sustainable agro-ecosystems. [ABSTRACT FROM AUTHOR]

Background and aims : N nutrition index (NNI) diagnosis and N requirement (Nfr) estimation are essential for accurate N management in the fertirrigation system. However, the NNI after straw retention and the relationships between NNI, Nfr, and relative yield (RY) are all not fully understood. Methods: A three years field trial with three straw incorporation methods (without straw (NI), with straw (SI), and straw-derived biochar incorporation (BI)) and five N rates (0, 150, 225, 300, and 375 kg ha−1) was conducted on drip-irrigated maize in northwest China. Soil NO3−-N content (CN), N recovery efficiency (REN), NNI, Nfr, and grain yield under NI, SI, and BI were compared. Later, the mathematical relationships between NNI, Nfr, and RY were defined. Results: Results showed that compared with NI, the N input during the reproductive stage could be reduced under SI and BI to achieve higher grain yield with NNI increased due to an increase in CN. In addition, Nfr was calculated by dividing N accumulation deficit (NAD) by REN, where a significant linear relationship existed between NAD and NNI (NAD = S(1-NNI)), and the slope of the NAD-NNI regression (S) varied quadratically with days after sowing (DAS). NNI and RY were also related in linear plus plateau functions, and the maximum RY was achieved when NNI was 0.88. Conclusions: Based on patterns of variance, three easily accessible independent variables (DAS, REN, and NNI) were used to create and verify Nfr estimating techniques for generating higher yields in maize under NI, SI, and BI. [ABSTRACT FROM AUTHOR]

Non- Saccharomyces yeasts have attracted great oenological interest due to their contribution to wine aroma, while the underlying mechanisms remain complex and insufficiently understood. To elucidate the potential mechanisms responsible for the high fruity esters production by P. kluyveri PK-19, a non- Saccharomyces yeast strain known for its aroma production, the nitrogen assimilation profile, fermentation capacity, and volatile production were compared with those of three other yeast strains, namely Saccharomyces cerevisiae SC-19, Pichia fermentans Z9Y-3, and Hanseniaspora uvarum Yun268. Despite the intermediate fermentation capacity, P. kluyveri PK-19 showed strong nitrogen consumption and rapid uptake of Ehrlich pathway-related amino acids during the early stages of alcoholic fermentation. Moreover, P. kluyveri demonstrated a high efficiency in converting Ehrlich pathway-related amino acids into their corresponding higher alcohol acetates (HAAs), indicating an enhanced ability to synthesize HAAs from Ehrlich pathway precursors. The rapid assimilation of Ehrlich pathway-related amino acids and efficient transformation to HAAs potentially contributed to the high production of HAAs in P. kluyveri PK-19. These results suggest that supplementing P. kluyveri -involved fermentation with Ehrlich pathway-related amino acids can increase HAA production and modify wine aroma profiles. [Display omitted] • Nitrogen requirement and adaptability of non- Saccharomyces were strain-dependent. • Early uptake of Ehrlich amino acids may contribute to high acetate ester production. • P. kluyveri showed high transformation efficiency from amino acid to acetate ester. • Poor uptake ability of non-preferred nitrogen sources was observed in H. uvarum. [ABSTRACT FROM AUTHOR]

Sesarmid crabs play an important role in mangrove biogeochemical processes due to their leaf-eating and burrowing activities. How leaf-eating mangrove crabs meet their nitrogen (N) needs remains a puzzle, as N-poor leaf litter (

Big data provide a pathway to lower crop nitrogen inputs from genetic breeding to field production. Moreover, multidisciplinary efforts from plant health sensing, deep machine learning and cloud computing can integrate multi-source data to form information and knowledge. So big data analysis as a prospective optimal method, will make leaps towards addressing future issues of sustainable agriculture.

Aim: There is increasing recognition that plant–soil feedbacks drive species co‐existence; therefore the below‐ground compartment should be better considered in ecological restoration. Addition of carbon is a restoration measure that relies on indirect plant–soil relationships by immobilizing soil nitrogen in microbial biomass to manipulate competitive hierarchies between plant species. The aim of the present work was to evaluate the impact of six years of carbon amendment in old‐field restoration in the long term, 20 years after the first application. Location: Old‐fields and reference sand steppe on dry calcareous sandy soil in Fülöpháza, Kiskun LTER site (46°53′ N, 19°24′ E), Hungary, Pannonian biogeographic region, Europe. Methods: We applied carbon amendment in the form of sucrose and sawdust on three abandoned agricultural fields between 1998 and 2003. Vegetation was surveyed in 1998–2006 and re‐sampled in 2008, 2010 and 2018 on permanent 2 m × 2 m coenological relevés for carbon‐amended, control and reference plots (n = 144). We used principal response curves (PRC) to describe vegetation development trajectories and linear mixed‐effects models to test changes in cover of vascular plants and cryptogams, nitrogen requirement groups and restoration species groups with time and treatment. Results: Carbon amendment resulted in lower soil nitrogen availability, and lower cover of vascular plants and cryptogams compared to control, but these differences became visible only four to five years after the first application and disappeared three years after the cessation of treatment. Minor treatment effects on the cover of oligotrophic, mesotrophic and target species were found. Conclusions: Carbon amendment did not speed up the recovery of sand grasslands; however, the reduction of cover (vegetation and cryptogam) can be a window of opportunity for other species to colonize that can be used as a complement to other treatments. Long‐term monitoring is especially important in evaluating restoration interventions that focus on indirect above‐ground–below‐ground linkages. [ABSTRACT FROM AUTHOR]

Background: Nutritionally, there is a dietary requirement for indispensable amino acids (IAAs) but also a requirement for nitrogen (N) intake for the de novo synthesis of the dispensable amino acids (DAAs). It has been suggested that there might be a dietary requirement for specific DAAs.Objectives: Experiment 1 tested whether 9 of the DAAs (Ala, Arg, Asn, Asp, Gln, Glu, Gly, Pro, Ser) are ideal N sources using the indicator amino acid oxidation (IAAO) technique. Experiment 2 examined whether there is a dietary requirement for Glu in adult men.Methods: Seven healthy men (aged 20-24 y) participated in 11 or 2 test diet intakes, in experiment 1 and 2, respectively, in a repeated measures design. In experiment 1, a base diet consisting of the IAA provided at the RDA was compared with test intakes with the base diet plus addition of individual DAAs to meet a 50:50 ratio of IAA:DAA on an N basis. In experiment 2, the diets corresponded to the amino acid pattern present in egg protein, in which all Glu and Gln was present as Glu, or removed, with Ser used to make the diets isonitrogenous. On each study day the IAAO protocol with l-[1-13C]phenylalanine was used to measure whole-body protein synthesis.Results: In experiment 1, repeated measures ANOVA with post hoc multiple comparisons showed that 7 of the 9 DAAs (Ala, Arg, Asn, Asp, Glu, Gly, Ser) decreased IAAO significantly (P < 0.05) compared with base IAA diet, the exceptions being Gln and Pro. In experiment 2, a paired t test did not find significant (P > 0.05) differences in the IAAO in response to removal and replacement of Glu intake.Conclusions: The results suggest that in healthy men most DAAs are ideal N sources for protein synthesis, in the presence of adequate IAAs, and that endogenous synthesis of Glu is sufficient.Registered clinicaltrials.gov identifier: NCT02009917. [ABSTRACT FROM AUTHOR]

Precision nitrogen (N) management (PNM) serves as a promising strategy for meeting the dual goals of food security and agricultural sustainable development by matching crop N demand with soil N supply in time and space. Previous studies have focused on in-season estimation of crop N nutrition index (NNI) and N requirement (NR) to diagnose plant N status and facilitate PNM. However, direct application of NNI and NR in N fertilizer management remains limited. The objective of this study was to develop an NNI-based N recommendation algorithm (NNI-PNM) for wheat and evaluate its effectiveness compared with local management and multi-objective optimization strategies in terms of agronomic, economic benefits and environmental impacts. The dynamic relationships between NR and NNI were analyzed across wheat growth stages and integrated into an N recommendation model. Based on the yield response to N fertilizer, the performance of the NNI-PNM strategy was simulated under different N status scenarios from four site-year N plot experiments with different N levels and varieties. Then, Pareto-based ranking and life cycle assessment approaches were used to investigate the comprehensive potential of the NNI-PNM strategy in five farmers' field experiments. The results indicated that NNI and NR were significantly correlated (R2 = 0.54–0.98), with their slopes increasing as days after sowing increased and N recovery efficiency decreased. Based on this pattern, the estimated NR values closely matched the observed NR values (RMSE = 3.0–13.7 kg ha−1, RE = 23–36%). The topdressing N rates simulated by the NNI-PNM strategy varied with N status, with increasing yield (0.36–0.66 t ha−1) and N partial factor productivity (16.8–21.6%) under N deficiency and N surplus conditions, respectively, compared with regional optimal N management. Moreover, the NNI-PNM strategy reduced N rates by 42% and global warming potential by 28.8%, and increased N use efficiencies by 78.4% without any reduction in grain yield, grain protein concentration, and net ecosystem economic benefits compared with farmer's conventional practices. The NNI-PNM strategy based on a robust relationship between NR and NNI is a simple yet effective tool for aiding smallholders in decision-making about fertilizer application. The developed strategy performed better in achieving multi-objective optimization (food security, economic benefits, and environmental quality) than farmers' current practices. These findings demonstrate the potential of the NNI-PNM strategy in optimizing wheat production for multi-objective benefits and provide valuable insights for promoting agricultural sustainability in small-scale farming systems. • Nitrogen topdressing strategy based on nitrogen nutrition index was developed. • Nitrogen topdressing strategy responded better to nitrogen nutrient status. • This strategy achieved multi-objective optimization (food, environment, and economy). • This study offered a promising solution for promoting agricultural sustainability. [ABSTRACT FROM AUTHOR]

Introduction: Nitrogen (N) is one of the most important growth-limiting nutrients for dryland wheat. Mineral nitrogen or ammonium (NH4+) and nitrate (NO3−) are two common forms of inorganic nitrogen that can serve as limiting factors for plant growth. Nitrogen fertilization in dryland area can increase the use of soil moisture, and improve wheat yields to some extent. Many researchers have been confirmed interactions between water stress and nitrogen fertilizers on wheat, especially under field conditions. Because of water stress affects forms of nitrogen uptake that leads to disorder in plant metabolism, reduction in grain yield and crop quality in dryland condition. On the other hand, use of suitable methods for determining nitrogen requirement can increase dryland wheat production. However, nitrogen recommendations should be based on soil profile content or precipitation. An efficient method for nitrogen fertilizer recommendation involves choosing an effective soil extractant and calibrating soil nitrogen (Total N, NO3− andNH4+) tests against yield responses to applied nitrogen in field experiments. Soil testing enables initial N supply to be measured and N supply throughout the season due to mineralization to be estimated. This study was carried out to establish relationship between nitrogen forms (Total N, NO3− andNH4+) in soil and soil profile water content with plant response for recommendation of nitrogen fertilizer. Materials and Methods: This study was carried out in split-split plot in a RCBD in Dryland Agricultural Research Institute (DARI), Maragheh, Iranwhere N application times (fall, 2/3 in fall and 1/3 in spring) were assigned to the main plots, N rates to sub plot (0, 30, 60 and 90 kg/ha), and 7 dryland wheat genotypes to sub-sub plots (Azar2, Ohadi, Rasad and 1-4 other genotypes) in three replications in 2010-2011. Soil samples were collected from 0-20, 20-40, 40-60 and 60-80 cm in sub-sub plots in shooting stage (ZGS32). Ammonium measurement in the soil KCl extracts was down by spectrophotometry method and colorimetric reaction at 655 nm. Also, Absorption spectrophotometry method was used for determination of nitrate in soil extract based on its UV absorbance at 210 nm. In this method two measurements were carried out; one before (by Zn coated by Cu) and second after reduction of nitrate). Using the difference between these two measurements, concentration of nitrate in the extracts was determined. Soil water content was also measured with Diviner 2000 after calibration in 0-20, 20-40, 40-60 and 60-80 cm soil profile in sub-sub plots. After wheat harvest, the most suitable regression model between soil mineral nitrogen (Nm) and soil moisture (θ) was fitted with wheat grain yield by DataFit version 9.0 software. Results and Discussion: The best model between soil N forms (nitrate, ammonium and mineral nitrogen) was calibrated between mineral nitrogen (Nm) and soil moisture (θ) with crop response (Y=a+bN_m+c ln⁡〖(θ)〗+dN_m^2+eln⁡〖(θ)〗^2+fN_m ln⁡〖(θ)〗) that explained 80% of dryland wheat yield variations. In this model, the contributions of mineral nitrogen (NO3− +NH4+) were 26%, soil moisture 50% and their interactions 24%. According to this model, the effect of soil moisture on production of grain yield was 2.3 folds greater than the mineral N. These results are most suitable for sampling and calibration of mineral nitrogen in 0-40 cm in dryland wheat stem elongation (ZGS32). Critical value of soil mineral N was 41 kg/ha, equal to 18.0 mg Nm/kg in this layer for obtaining higher grain yield (over 2500 kg/ha). According to regression model, application of 50 kg N/ha in autumn was able to provide Nm critical level in 0-40 cm layer for dryland wheat genotypes under experimental conditions. Also simulation model showed that nitrogen fertilizer increased grain yield and it is more than the soil mineral nitrogen. If the soil mineral nitrogen is 20 kg/ha or less in 0-40 cm soil layer, there may be increase of grain yield up to 4000 kg/ha through the application of nitrogen fertilizers. Therefore, increasing of mineral nitrogen in the soil profile up to 20 kg/ha is not appropriate for wheat production in Northwest of Iran drylands. Conclusion: It can be concluded that, there is a relationship between soil nitrogen and moisture content with dryland wheat response and suggested model can be used for nitrogen recommendations for dryland wheat. According to the model, the effects of nitrogen fertilizer application on grain yield were much more than the effect of soil mineral nitrogen. Therefore, the increasing of soil nitrogen storage is not recommended in dryland conditions.

Reducing the fertiliser nitrogen (N) requirement of oilseed rape ( Brassica napus L.) whilst maintaining yield will be beneficial for both growers and the environment. The aim of this paper was to identify differences in fertiliser N requirement between varieties and investigate simple in-field methods to rapidly identify varieties that can maintain high yield whilst requiring lower optimal N rates (‘HYLO’ varieties) to aid breeding for lower N fertiliser requirement. Four field experiments were conducted in the UK during seasons 2011-12 or 2012-13 on a range of soil types. Each experiment included 21 elite open pollinated and hybrid varieties. Each variety was grown at seven levels of N fertiliser ranging from zero to super-optimal (340 or 400 kg N/ha). Measurements of seed yield and seed oil content were combined to calculate gross output yield, i.e. seed yield adjusted for oil content. Linear plus exponential yield response curves were fitted to calculate the economically optimum N rate (Nopt) of each variety and the associated nitrogen use efficiency (NUE) was calculated at the Nopt. Across varieties, gross output yield responses to optimum N fertiliser, compared with yields at nil N rates, were significant, ranging from 1.3 to 2.7 t/ha between sites. Nopt ranged from 117 to 286 kg N/ha between sites giving experimental average yields at Nopt (Yopt) of 3.0 to 4.6 t/ha. Varietal yield ranges at Nopt within each experiment ranged from 0.6 to 1.7 t/ha, and there was a positive trend for yield to increase with date of variety introduction by 0.24 t/ha per decade. Significant variety x N fertiliser rate interactions were measured for gross output yield in two out of four experiments and significant varietal differences in Nopt were measured in one experiment ranging from 195 kg N/ha to 296 kg N/ha. There was no correlation between Nopt and Yopt indicating that improving varietal yield potential will not necessarily increase N requirement. Significant varietal differences in NUE were measured at Nopt ranging from 13.5 to 15.9 kg of gross output yield per kg of N supply from soil residues and fertiliser. Seed with low N and high oil content, and high biomass harvest index could be useful indicators of high NUE. However, no single trait correlated consistently with varietal variation in NUE. The yield difference between sub- and super-optimal N rates was positively correlated with Nopt. Further research is required to develop new experimental approaches for measuring yield at more than one N level on small experimental plot areas and to investigate a wider range of genotypes. [ABSTRACT FROM AUTHOR]

Background: Dietary ammonia is rapidly absorbed but poorly used for urea synthesis in pigs fed low-crude-protein (low-CP) diets deficient in dispensable amino acid (DAA)-nitrogen.Objective: We explored the effect of dietary ammonia on net amino acid (AA) balances in portal-drained viscera (PDV) and livers of pigs fed a diet deficient in DAA-nitrogen.Methods: Eight barrows with an initial body weight (BW) of 26.5 ± 1.4 kg (mean + SD) were surgically fitted with 4 catheters each (portal, hepatic, and mesenteric veins and carotid artery). The pigs were restricted-fed (2.8 × 191 kcal/kg BW0.60) for 7 d, and every 8 h a diet deficient in DAA-nitrogen supplemented with increasing amounts of ammonia-nitrogen (CP = 7.76%, 9.27%, and 10.77% for the control and low- and high-ammonia diets, respectively). The treatment sequence was based on a 3 × 3 Latin-square design with 3 consecutive periods. On the last day of each period, blood flows in portal and hepatic veins were determined with a continuous infusion of ρ-amino hippuric acid into the mesenteric vein. Consecutive blood samples were taken for AA concentration in blood plasma, and AA balances were calculated for PDV and the liver.Results: Cumulative release of citrulline (Cit) and proline (Pro) increased with ammonia supplementation in PDV but decreased for glutamine (Gln) and glycine (Gly) (Gln: -19.32 ± 3.56, -32.50 ± 3.73, and -42.11 ± 3.55 mmol/meal for the control and low- and high-ammonia groups, respectively; P ≤ 0.05). Cumulative release of alanine (Ala), glutamic acid (Glu), and Gln increased with ammonia supplementation across the liver (P ≤ 0.05). When combined, PDV+liver, the cumulative release of Ala, Cit, and Glu increased with ammonia-nitrogen supplementation (P ≤ 0.05).Conclusion: Dietary ammonia could be used as a nitrogen supplement to increase the synthesis of Ala, Cit, and Glu across splanchnic organs in pigs fed a diet deficient in DAA-nitrogen. [ABSTRACT FROM AUTHOR]

Betula alnoides is a fast-growing hardwood species grown in large plantations in Southeast Asia and South China. Nitrogen requirements for producing robust seedlings, growth and nutrient dynamics were investigated using exponential fertilization treatments. Root collar diameter, height, dry mass and nutrient contents of seedlings increased exponentially in all fertilization treatments as time progressed. Moreover, with water soluble fertilizer (Plant Products plus microelements N-PO-KO: 20-20-20), 300 mg N seedling was adequate. Vector analysis revealed that P was the most responsive nutrient element, followed by N and K. Dilutions of N and K were evident in the plants without N addition, which induced initial P sufficiency and then luxury consumption probably due to the antagonistic interaction between N and P. However, deficiencies of N, P and K were mostly observed in all exponential regimes during the experiment because seedling growth rate exceeded nutrient uptake rate, inferring that further study on improving the nutrient uptake efficiency is needed. Analysis of relationships among nutrient supply, dry mass, N content and N concentration demonstrated that 100-400 mg N seedling induced sufficiency to luxury consumption of nitrogen without significant change in dry mass, and 400 mg N seedling is recommended to apply for nutrient loading of seedlings before outplanting. The findings will help improve seedling quality and enhance the production of robust seedlings for plantation forestry of this species. [ABSTRACT FROM AUTHOR]

Background: Including ammonia in low-crude protein (CP) diets deficient in dispensable amino acid (DAAs) increases nitrogen retention in growing pigs.Objective: We investigated the absorption and metabolism of dietary ammonia nitrogen in the portal-drained viscera (PDV) and liver of pigs fed a diet deficient in DAA nitrogen.Methods: Eight pigs with an initial mean ± SD body weight (BW) of 26.5 ± 1.4 kg were surgically fitted with 4 catheters each (portal, hepatic and mesenteric veins, and carotid artery). The pigs were fed (2.8 × 191 kcal/kg BW0.60), for 7 d and every 8 h, a diet deficient in DAA nitrogen supplemented with increasing amounts of ammonia nitrogen (CP: 7.76%, 9.27%, and 10.77%; indispensable amino acid nitrogen:total nitrogen ratio: 0.71, 0.59, and 0.50 for control and low- and high-ammonia diets, respectively). The treatment sequence was based on a Latin square design with 3 consecutive periods. On the last day of each period, blood flows in the portal and hepatic veins were determined with a continuous infusion of ρ-amino hippuric acid into the mesenteric vein. Serial blood samples were taken to determine ammonia and urea nitrogen concentration. Net balances of ammonia and urea nitrogen were calculated for the PDV and liver.Results: Cumulative (8 h) ammonia nitrogen appearance in the portal vein increased (P ≤ 0.05) with ammonia intake (433, 958, and 1629 ± 60 mg ammonia nitrogen/meal for control and low- and high-ammonia diets, respectively). The cumulative hepatic uptake of ammonia nitrogen increased (P ≤ 0.05) with ammonia nitrogen supply. The cumulative urea nitrogen appearance in the hepatic vein tended to increase (P ≤ 0.10) only in high-ammonia treatment (-92.5, -59.4, and 209.7 ± 92 mg urea nitrogen/meal for control and low- and high-ammonia diets, respectively) and, relative to the control diet, represented -6.0% and 11% of ammonia nitrogen intake.Conclusion: Dietary ammonia nitrogen is poorly utilized for urea production across splanchnic organs when pigs are fed diets deficient in DAA nitrogen. [ABSTRACT FROM AUTHOR]

Estimating in-season N requirement (NR) is essential for managing N fertilizer application in crop production. Critical N (N c ) dilution curve is an effective and simple-to-use technique for assessment of in-season crop N status, yet its adaptation to make field decisions about dressing N fertilization remains to be determined. This study was endeavored to establish the relations between NR, N nutrition index (NNI) and relative yield (RY) at different crop growth stages in Japonica and Indica rice ( Oryza sativa L.) eco-types and to estimate time-course NR for recommending supplemental N fertilization on N c dilution curve basis. Four field experiments of multi-N rates were carried out in east China using three Japonica and two Indica rice hybrids. Growth analysis was carried out at different growth stages from active tillering (AT) to heading (HD). The estimated NR under varied N rates has well differentiated the sub-optimal, optimal and supra optimal growth conditions at different stages in both rice eco-types. The NR-NNI and RY-NR relations for both rice eco-types at different growth stages were highly significant with R 2 values greater than 0.88 and 0.95 for NR-NNI, and 0.83 and 0.91 for RY-NR relations, respectively, the highest R 2 values for both eco-types were 0.98 and 0.99 for NR-NNI and 0.94 and 0.93 for RY-NR relations at panicle initiation (PI) and booting (BT) stages. Validation of the regression models with two independent datasets exhibited a solid model performance at PI and BT stages, with R 2 values greater than 0.96 for NR-NNI while 0.94 for RY-NR relations. Moreover, the root mean square error (RMSE) values lower than 20% for NR prediction from NNI, while 8% for RY prediction from NR also confirmed the robustness of the relationships at PI and BT stages. The kappa (k) coefficients at PI and BT stages for observed and predicted NR and RY were close to 1. Generally, the robust relations at PI and BT stages well elucidated the variation in NR and RY both under deficient and optimum N growing conditions, and gave reliable estimation of NR for quantifying supplemental N fertilization for rice grown in east China. The results of this study will offer a suitable approach for managing N application precisely during the growth period of rice crop. [ABSTRACT FROM AUTHOR]

Non-destructive assessment of plant nitrogen (N) status is essential for efficient crop production and N management in intensive rice (Oryza sativa L.) cropping systems. Chlorophyll meter (SPAD-502) has been widely used as a rapid, non-destructive and cost-effective diagnostic tool for in-season assessment of crop N status. The present study was intended to establish the quantitative relationships between chlorophyll meters readings, plant N concentration (PNC), N nutrition index (NNI), accumulated N deficit (AND), and N requirement (NR), as well as to compare the stability of these relationships at different vegetative growth stages in Japonica and Indica rice cultivars. Seven multi-locational field experiments using varied N rates and seven rice cultivars were conducted in east China. The results showed that the PNC and chlorophyll meters readings increased with increasing N application rates across the cultivars, growing seasons, and sites. The PNC and chlorophyll meters readings under varied N rates ranged from 2.29 to 3.21, 1.06 to 1.82 and 37.10 to 45.4 and 37.30 to 46.6, respectively, at TL and HD stages for Japonica rice cultivars, while they ranged from 2.25 to 3.23, 1.34 to 1.91 and 35.6 to 43.3 and 37.3 to 45.5 for Indica rice cultivars, respectively. The quantitative relationships between chlorophyll meters readings, PNC, NNI, AND, and NR established at different crop growth stages in two rice ecotypes, were highly significant with R2 values ranging from 0.69 to 0.93 and 0.71 to 0.86 for Japonica and Indica rice, respectively. The strongest relationships were observed for AND and NR at panicle initiation and booting stages in both rice ecotypes. The validation of the relationships developed in the present study with an independent data exhibited a solid model performance and confirmed their robustness as a reliable and rapid diagnostic tool for in-season estimation of plant N parameters for sustainable N management in rice. The results of this study will offer a suitable approach for managing N application precisely during the growth period of the rice crop in intensive rice cropping systems in east China.

A field experiment was conducted at the Field Crops Research and Development Institute, Mahailluppllama to identify an optimum seed rate and the respective nitrogen level for broadcast blackgram grown on rainfed uplands during Maha 2009/2010 with the variety MI-1. The study was carried out as a two factor factorial experiment. Six seed rates (25 kg/ha, 37.5 kg/ha, 50 kg/ha, 62.5 kg/ha, 75 kg/ha, 87.5 kg/ha) with two rates of nitrogen (30 kg of N/ha, Zero N) were the two factors tested in the experiment. The results revealed that the plant height, leaf area per plant and canopy diameter did not vary with the seed rate but significantly varied with fertilizer rates. Number of pods per plant, number of seeds per pod and 1000 seed weight did not vary with the seed rate but number of pods per plant and 1000 seed weight varied with the fertilizer level. The maximum yield was recorded at a seed rate of 64 kg/ha. Economic analysis revealed that the optimum seed rate is 62.5 kg/ha. The number of plants/ m2 at which maximum yield was obtained was estimated as 93 plants/m2 which is also comparable to this seed rate. As there were no differences observed in yield components except for the number of plants per unit area, the main contributing factor for yield increments with increasing seed rate was the number of plants per unit area. Therefore, it can be concluded that the optimum seed rate for broadcast crop of black gram under rain-fed conditions is 62.5 kg/ha when N is supplied at the rate of 30 kg/ha. Key words: Blackgram; Nitrogen requirement; Optimum rate seed DOI: 10.4038/tar.v22i2.2825Tropical Agricultural Research Vol. 22 (2): 165-171 (2011)

Non-destructive assessment of plant nitrogen (N) status is essential for efficient crop production and N management in intensive rice (Oryza sativa L.) cropping systems. Chlorophyll meter (SPAD-502) has been widely used as a rapid, non-destructive and cost-effective diagnostic tool for in-season assessment of crop N status. The present study was intended to establish the quantitative relationships between chlorophyll meters readings, plant N concentration (PNC), N nutrition index (NNI), accumulated N deficit (AND), and N requirement (NR), as well as to compare the stability of these relationships at different vegetative growth stages in Japonica and Indica rice cultivars. Seven multi-locational field experiments using varied N rates and seven rice cultivars were conducted in east China. The results showed that the PNC and chlorophyll meters readings increased with increasing N application rates across the cultivars, growing seasons, and sites. The PNC and chlorophyll meters readings under varied N rates ranged from 2.29 to 3.21, 1.06 to 1.82 and 37.10 to 45.4 and 37.30 to 46.6, respectively, at TL and HD stages for Japonica rice cultivars, while they ranged from 2.25 to 3.23, 1.34 to 1.91 and 35.6 to 43.3 and 37.3 to 45.5 for Indica rice cultivars, respectively. The quantitative relationships between chlorophyll meters readings, PNC, NNI, AND, and NR established at different crop growth stages in two rice ecotypes, were highly significant with R2 values ranging from 0.69 to 0.93 and 0.71 to 0.86 for Japonica and Indica rice, respectively. The strongest relationships were observed for AND and NR at panicle initiation and booting stages in both rice ecotypes. The validation of the relationships developed in the present study with an independent data exhibited a solid model performance and confirmed their robustness as a reliable and rapid diagnostic tool for in-season estimation of plant N parameters for sustainable N management in rice. The results of this study will offer a suitable approach for managing N application precisely during the growth period of the rice crop in intensive rice cropping systems of east China. [ABSTRACT FROM AUTHOR]

Crop nitrogen (N) status during vegetative growth is an essential indicator of crop vigor and predictor of subsequent grain yield. The concept of the critical nitrogen (Nc) dilution curve has been used for in-season assessment of crop N status, yet it remains to be determined that how plant N status during vegetative growth can be related to grain yield at maturity in rice. The present study was endeavored to establish the relationships of relative grain yield (RY) to N nutrition index (NNI), accumulated N deficit (AND), and N requirement (NR) at different growth stages of Japonica and Indica rice on the basis Nc dilution curve of the rice plant. Four multi-N rate field experiments were conducted in Jiangsu province of east China using five rice hybrids. Growth analysis was carried out to determine the Nc dilution curve and related N parameters during vegetative growth period. The relationships between RY and NNI, AND, NR at different growth stages were highly significant with R 2 values all greater than 0.74 for both Japonica and Indica rice, with the strongest R 2 ranging from 0.94 to 0.99 for the relationships at panicle initiation (PI) and booting (BT) stages. Validation of the regression models with independent datasets exhibited a solid model performance at PI and BT stages with R 2 values greater than 0.92 and RMSE values lower than 10%, confirming the robustness of the relationships at PI and BT stages. The k coefficients at PI and BT stages for the observed and predicted RY were close to 1. Overall, the robust relationships of RY to NNI, AND and NR at PI and BT stages well explained the variation in RY under limiting and non-limiting N growth conditions, and gave a reliable estimation of rice grain yield in east China. [ABSTRACT FROM AUTHOR]

Nitrogen (N) resorption is a key strategy for conserving N in forests, and is often affected by soil nutrient condition and N sink strength within the plant. However, our understanding of the age-related pattern of N resorption and how increasing N deposition will affect this pattern is limited. Here, we investigated N resorption along a chronosequence of stands ranging in age from 2 to 100 years old, and conducted a 4-year exogenous N input experiment in stands at age class 11, 20, and 45 in a Larix Principis- rupprechtii plantation in north China. We found a logarithmic increase in leaf N resorption efficiency (NRE) and green leaf N concentration, and a logarithmic decrease in senesced-leaf N concentration along the stand-age chronosequence. Leaf NRE was negatively correlated with plant-available N concentration. Stand-level N resorption was positively correlated with the annual N requirement for tree growth. N resorption contributed to 45, 62, and 68% of the annual N supply in the 11-, 20-, and 45-year-old stands, respectively. Our exogenous N input experiment showed that leaf NRE in the 11- and 20-year-old stands decreased 17 and 12% following a 50-kg N ha y input. However, leaf NRE was not affected in the 45-year-old stand. The increases in leaf NRE and the contribution of N resorption to annual N supply along stand ages suggested that, with stand development, tree growth depends more on N resorption to supply its N need. Furthermore, the leaf NRE of mature stand was not decreased under exogenous N input, suggesting that mature stands can be stronger sinks for N deposition than young stands due to their higher capacity to retain the deposited N within plants via internal cycle. Ignoring age-related N use strategies can lead to a bias in N cycle models when evaluating forest net primary production under increasing global N deposition. [ABSTRACT FROM AUTHOR]

Nitrogen (N) management is critical in sugarbeet production to optimize yield and quality. Although, past research has been critical to improving and understanding sugarbeet N nutrition, continued research is needed to evaluate evolving varieties and management practices. From 2005 to 2010, studies from 14 locations (14 site-years) were conducted by agronomists from The Amalgamated Sugar Company (TASCO) and scientists at the USDA-ARS Northwest Irrigation and Soils Research Laboratory to evaluate the effect of N supply (fertilizer N + spring soil residual N [Nitrate N (NO3-N) + Ammonium N (NH4-N)]) on sugarbeet production in the Pacific Northwest. At each site-year, the effect of various levels of N supply on estimated recoverable sucrose (ERS) yield, root yield, sucrose concentration, brei nitrate concentration, and nitrogen use efficiency (NUE) were assessed. Nitrogen supply significantly affected ERS yield for 6 of the 14 site-years. For the 8 non-responsive sites, the maximum ERS yield was assumed to be the lowest N supply. The average nitrogen requirement (Nr) at maximum ERS yield across all site-years was 2.25 kg N Mg-1 beet and ranged from 1.4 to 3.7 kg N Mg-1 beet. Thirteen of the 14 site-years had an Nr at or below 2.8 kg N Mg-1 beet, substantially less than current recommendations of 3.5 to 4.0 kg N Mg-1 beet. Nitrogen requirements can be reduced in the Pacific Northwest sugarbeet production area compared to past recommendations resulting in reduced N fertilizer applications and significant cost savings. [ABSTRACT FROM AUTHOR]

Background: Nitrogen absorption from the large intestine is considered of limited value for supporting body protein synthesis in animals and humans, but it may beof benefit when the dietary supply of nitrogen for synthesis of dispensable amino acids (DAAs) is deficient. Objective: A whole-body nitrogen balance study was conducted to evaluate the impact of nitrogen absorption from the large intestine of pigs fed a diet deficient in DAA nitrogen. Methods: Nine cecally cannulated barrows were fed a cornstarch and casein-based diet with a high indispensable amino acid (IAA) nitrogen to total nitrogen ratio (IAA:TN; 0.75). Pigs were randomly assigned to saline or 1 of 2 urea nitrogen infusion rates into the cecum (low and high, 1.5 and 3.0 g/d, respectively) following a 333 Latin square design. At the high urea nitrogen infusion rate, IAA:TN was 0.55. At slaughter, liver samples were taken to measure activity of carbamoyl phosphate synthetase I (CPS-I), glutamate dehydrogenase (GDH), and Gln synthetase (Gln-S). Results: Whole-body nitrogen retention improved with urea infusion (4.86 ± 0.20 g/d, 6.40 ± 0.21 g/d, and 7.75 ± 0.19 g/d for saline and low and high infusion rates, respectively; P< 0.05), as well as body weight gain. The marginal efficiency of using nitrogen absorbed from the large intestine for improving nitrogen retention was not affected by urea nitrogen infusion rate (P> 0.10). Enzyme activity of CPS-I or Gln-S was not different between treatments (P> 0.10), but GDH showed a trend for a positive linear response with increasing urea nitrogen infusion rate (P = 0.06). Conclusion: These results indicate that urea nitrogen absorbed from the large intestine is efficiently used for increasing body protein deposition when feeding pigs a diet deficient in DAA nitrogen. [ABSTRACT FROM AUTHOR]

For nectar-feeding birds, the low amino acid and protein content of nectar is likely a major nutritional constraint. Nectar-feeding birds present morphological, behavioral, and physiological adaptations that allow them to exploit nectar efficiently. One of these adaptations might be a low nitrogen requirement compared to birds of taxa that rely on other resources. The Bananaquit ( Coereba flaveola) is considered a specialized nectar-feeding passerine. It is widely distributed in the Neotropics and one of the most abundant flower-visiting passerine in northern Venezuela. We measured maintenance nitrogen requirement (MNR) and total endogenous nitrogen loss (TENL) in captive Bananaquits fed on four diets of varying concentrations of protein (0, 1.5, 3.0, and 7.0 %). We found that the Bananaquit had a MNR of 8.7 mg N day (313.2 mg N W day) and a TENL of 3.3 mg N day (111 mg N W day), values in the high range of what was previously reported for other nectar-feeding birds. However, when compared to other species with different feeding habits (i.e. granivores) the Bananaquit presents a low nitrogen requirement. These high values suggest different physiological and behavioral strategies from other nectar-feeding birds or methodological issues associated to an unbalanced diet based on a protein plant source. [ABSTRACT FROM AUTHOR]

The sugarbeet industry in the Pacific Northwest is interested in strip tillage (ST) primarily due to the potential savings in tillage costs. This study was conducted to evaluate the use of ST in the Pacific Northwest compared to conventional tillage (CT) practices and to evaluate N requirements of sugarbeet under ST and CT. The effect of tillage method (ST, moldboard plow [MP] system, and chisel plow [CP] system) and N supply (5 levels) on sugarbeet production factors were investigated in Kimberly, ID from 2008 to 2010 on a Portneuf silt loam soil with barley as the previous crop. Root and estimated recoverable sucrose (ERS) yields were the same under all three tillage practices across N supply. There were no differences in N response across tillage systems. However, estimated tillage costs for ST were from 53% to 76% lower than other tillage systems tested. The CP treatment had a significantly lower harvest plant population compared to ST and MP, likely because residue inhibited seed-soil contact. Averaged across tillage practices, in 2008 and 2010, a significant quadratic relationship was observed between N supply and root and ERS yield. During 2008 and 2010, yields at the economically optimum N supply (EONS) ranged from 73.6 to 79.9 Mg roots ha-1 and 11,054 to 11,415 kg ERS ha-1 across tillage practice and N prices ranging from $0.44 to $2.20 kg-1 N. During 2008 and 2010, nitrogen use efficiency (NUE) at the EONS ranged from 50.1 to 67.9 kg sucrose kg-1 N supply over all tillage practices and N prices. The N requirements at the EONS ranged from 2.4 to 3.0 kg Mg-1 in 2008 and 2.5 to 2.8 kg Mg-1 in 2010 over tillage practices and the range of N prices. Strip tillage can be used to obtain yields comparable to other common tillage practices and decrease tillage costs. Nitrogen requirements for all tillage practices could be reduced on heavier textured soils compared to past recommendations in the Pacific Northwest. However, adjusting N requirements based on sugarbeet production and quality history, soil type, and soil residual N should be evaluated. [ABSTRACT FROM AUTHOR]

Adequate availability of nitrogen (N) to satisfy potato crop N requirement is critical for production of optimal tuber yields with high processing qualities, which will contribute to maximum net returns. The agroclimatic conditions in the Columbia Basin region in the Pacific Northwest (PNW) supports high potato tuber yields with high processing qualities. Best management of N fertilization is important to increase N uptake efficiency and to minimize N losses. Monitoring soil and petiole N provides a basis to evaluate available N in the soil and N status in the plants. This study was conducted on a Quincy fine sand (mixed, mesic Xeric Torripsamments; >95% sand) using 'Ranger Russet' potato cultivar. Potato followed by 2 years of sweet corn rotation was adapted in this study. Treatments included the following preplant (PP) + in-season (IS) N rates in kg ha-1: (i) 56 + 280, (ii) 112 + 224, or (iii) 112 + 336 in 2004 or 112 + 112 in 2005. The IS N was applied in five equally divided doses at 2-week intervals, 3 weeks after seedling emergence. An additional treatment was included with treatment (ii) N rates, except that IS N was delivered in 10 weekly applications. Total tuber yield ranged from 54 to 64 and 78 to 90 Mg ha-1, respectively, in 2004 and 2005. In 2004, during the first 65 days after emergence (DAE), petiole nitrate (NO3) concentration was lower in the treatment (i) than that in the other treatments. This difference was not evident in 2005. The petiole NO3 concentrations were lower in 2005 than that in 2004, particularly during latter part of the growing period. Soil available N [nitrate NO3-N + ammonium (NH4) N in the top 30 cm] concentrations were also greater in 2004 than those in 2005. Soil N appeared to increase toward the end of the growing season in 2004, which has negative effects on tuber yield and quality. Across all treatments, total tuber yield and that of >340-g grade tubers were greater in 2005 than that in 2004. [ABSTRACT FROM AUTHOR]

1. Agricultural damage by wildlife is a serious constraint on the coexistence of humans and wildlife. Understanding the behavioural processes involved in such agricultural damage will inform management actions. In this study, a linear programming model based on optimal foraging theory was used to formulate management strategies designed to reduce wheat damage caused by white-fronted geese Anser albifrons around Lake Miyajimanuma in Japan. 2. Geese feed on rice grains or wheat leaves. Their choice of food is constrained by their daily energy requirement, daily nitrogen requirement, digestive capacity and daily maximum foraging time. With these constraints, we predicted the proportion of geese that should forage on wheat leaves under energy-maximizing, nitrogen-maximizing and time-minimizing strategies, and compared the results with the observed proportion. 3. Our predictions for the energy-maximizing strategy successfully explained the variation in the observed proportion of geese foraging on wheat leaves. It appeared that nitrogen constraints drove the geese to forage on wheat in autumn, but energy considerations drove the geese to forage on wheat plus rice in late spring. 4. Based on these results, we predicted that by increasing the harvest remains of rice by 30%, a large reduction in wheat damage could be achieved both in autumn and in spring. Damage could be reduced further by supplying protein-rich food, such as grass on fallow fields and on ridges of rice fields in autumn, and by leaving geese foraging in rice fields undisturbed. 5. Synthesis and applications. Optimal foraging models that consider foraging goals and constraints have considerable potential for identifying measures for minimizing agricultural damage problems caused by grazing bird species. Specifically, for geese grazing on wheat fields in Japan, we advocate increasing the availability of alternative protein-rich foods, such as rice harvest remains and grass, and minimizing disturbance to geese foraging on rice fields. Journal of Applied Ecology (2004) 41, 675 – 688 [ABSTRACT FROM AUTHOR]

The differences in nitrogen fixation, growth rate and numbers of cyanobionts and heterocysts among three Azolla pinnata var. pinnata strains were examined. The relative growth rate (RGR) and nitrogen fixation of PP7002 and PP7003 were significantly low compared with those of PP7005. The application of ammonium ions at 0.2 mM or more increased the growth rate of PP7002 and PP7003, but not PP7005. The numbers of cyanobionts and heterocysts in the mature region of PP7002 and PP7003 were statistically lower than those of PP7005. The low nitrogen-fixing activity of PP7002 and PP7003 as compared with PP7005 might be related to the restricted number of heterocysts. In PP7002 and PP7003, nitrogen fixation might be insufficient for full growth. [Copyright &y& Elsevier]

[Display omitted] • Crop yield and N requirement affected by combined N and P application rates. • Residual nitrate increased by N application but decreased when combined with P. • Nitrate in topsoil used to predict that in deep soil in wheat–maize cropping system. • Modified convenient method recommended for fertilizer application. The recommendations for soil fertilization based on soil testing are time-critical and labor-intensive for farmers in the winter wheat–summer maize double cropping system. Understanding the relationships between the crop yield, nitrogen requirement, and nitrate residue level under the combined N and P fertilizer application is necessary to optimize the fertilizer recommendation method in order to reduce the nitrate residue levels. In 2009, we established a long-term field fertilization experiment with five N application rates and four P application rates in the winter wheat-summer maize double cropping system. The grain yield, N requirement, and soil nitrate residue were determined during 2016–2019 to optimize the N inputs for nitrate residue control. The crop yield was increased by N application and it increased further when combined with P fertilizer. The N requirement of crops increased by N application but decreased when combined with P. The calculated maximum winter wheat yield was 7235 kg ha−1 and the theoretical N requirement for 1000 kg grain formation (N R) was 28.68 kg Mg−1. The maximum summer maize yield was 7866 kg ha−1, and the theoretical N R was determined as 23.43 kg Mg−1. The residual nitrate-N was increased by N application but decreased by combined P fertilizer. The correlation between the nitrate-N content in 0–20 cm top soil (S NC) and nitrate-N residue in 0–100 cm soil (S NR) was linear at the winter wheat harvest but exponential at the summer maize harvest. Thus, the S NR can be predicted by the S NC according to their correlation at the harvest. The predicted S NR at the harvest of the previous crop, the target yield and N R for the subsequent crop obtained from long-term in-situ observations can be used to guide the fertilizer amounts applied to the following crop. Therefore, we developed a convenient method to optimize the fertilizer recommendation method for the winter wheat–summer maize cropping system. [ABSTRACT FROM AUTHOR]

• Field, drone and satellite multispectral data provided comparable estimates of mid-season plant N status. • Random forest outperformed parametric regression by halving the RMSE of the predicted versus measured N status. • The drone data performed best in terms of accuracy for predicting mid-season N status. • Mid-season plant N requirement was accurately estimated based on the critical N dilution curve approach. Remote sensing can be used for precision nutrient management to assess plant nitrogen (N) status in a spatially detailed and real-time manner. Despite recent advances in satellite- and drone technology and machine learning, neither differences between platforms nor methodological aspects for estimating plant N status have been sufficiently investigated. In this study, multispectral data obtained by ground (handheld Rapidscan), air- (unmanned aerial vehicle, UAV) and spaceborne (Sentinel-2) platforms were exploited to estimate plant N uptake (PNU), concentration (PNC) and N nutrition index (NNI). The test plant was potato grown for three years on a sandy soil in Denmark and the analysis was based on the critical N dilution curve. Parametric (PR) and non-parametric (random forest, RFR) regressions were conducted and compared in predicting mid-season PNU , PNC and NNI from band reflectances or vegetation indices (VIs) derived from each platform data. The results obtained by the UAV data had the highest accuracy, largely due to the fine spatial resolution. For both regression types, PNU and NNI correlated better than PNC to reflectance data. For the UAV data, validation Nash-Sutcliffe model efficiency (NSE) of PNU and NNI ranged between 0.64–0.95 and 0.41–0.92 respectively, with corresponding values for relative root mean square error (RRMSE) of 7.1–22% and 5.86–22%. The lower end of NSE and higher end RRMSE intervals systematically being from the PR, which demonstrates the robustness and the high accuracy of RFR in predicting plant N status. The other platforms resulted in acceptable results, with validation NSE and RRMSE for PNU and NNI of, respectively, 0.60–0.79 and 14–20%, 0.25–0.79 and 10–17% for Rapidscan, and 0.48–0.83 and 17–28%, 0.42–0.82 and 12–19% for Sentinel-2. The band reflectance and the VIs were equally suited as input predictors for the RFR algorithm. The N requirement calculated from all three datasets reflected the field observations well. The study reveals the potential of different regression methods for detailed spatial estimation of plant N status to guide in-season fertilization by matching the plant growth demands, emphasizing the strengths of the RFR. The procedure is helpful for the digital agriculture and the smart farming industry aiming to avoid excess application of N. [ABSTRACT FROM AUTHOR]